(1) namespace file descriptors (nsfd)
(2) process file descriptors (pidfd)
When using nsfds the namespaces will remain active because they are
pinned by the vfs. However, when pidfds are used things are more
complicated.
When the target task exits and passes through exit_nsproxy_namespaces()
or is reaped and thus also passes through exit_cred_namespaces() after
the setns()'ing task has called prepare_nsset() but before the active
reference count of the set of namespaces it wants to setns() to might
have been dropped already:
// ns_active_ref_put() will also put
// the reference on the owner of the
// namespace. If the only reason the
// owning namespace was alive was
// because it was a parent of @ns
// it's active reference count now goes
// to zero... --------------------------------
// |
// ns->__ns_active_ref == 0 |
// parent_ns->__ns_active_ref == 0 |
| commit_nsset()
-----------------> // If setns()
// now manages to install the namespaces
// it will call ns_active_ref_get()
// on them thus bumping the active reference
// count from zero again but without also
// taking the required reference on the owner.
// Thus we get:
//
// ns->__ns_active_ref == 1
// parent_ns->__ns_active_ref == 0
When later someone does ns_active_ref_put() on @ns it will underflow
parent_ns->__ns_active_ref leading to a splat from our asserts
thinking there are still active references when in fact the counter
just underflowed.
So resurrect the ownership chain if necessary as well. If the caller
succeeded to grab passive references to the set of namespaces the
setns() should simply succeed even if the target task exists or gets
reaped in the meantime and thus has dropped all active references to its
namespaces.
The race is rare and can only be triggered when using pidfs to setns()
to namespaces. Also note that active reference on initial namespaces are
nops.
Since we now always handle parent references directly we can drop
ns_ref_active_get_owner() when adding a namespace to a namespace tree.
This is now all handled uniformly in the places where the new namespaces
actually become active.
ns: make sure reference are dropped outside of rcu lock
The mount namespace may in fact sleep when putting the last passive
reference so we need to drop the namespace reference outside of the rcu
read lock. Do this by delaying the put until the next iteration where
we've already moved on to the next namespace and legitimized it. Once we
drop the rcu read lock to call put_user() we will also drop the
reference to the previous namespace in the tree.
As announced a while ago this is the next step building on the nstree
work from prior cycles. There's a bunch of fixes and semantic cleanups
in here and a ton of tests.
Currently listns() is relying on active namespace reference counts which
are introduced alongside this series.
While a namespace is on the namespace trees with a valid reference count
it is possible to reopen it through a namespace file handle. This is all
fine but has some issues that should be addressed.
On current kernels a namespace is visible to userspace in the
following cases:
(1) The namespace is in use by a task.
(2) The namespace is persisted through a VFS object (namespace file
descriptor or bind-mount).
Note that (2) only cares about direct persistence of the namespace
itself not indirectly via e.g., file->f_cred file references or
similar.
(3) The namespace is a hierarchical namespace type and is the parent of
a single or multiple child namespaces.
Case (3) is interesting because it is possible that a parent namespace
might not fulfill any of (1) or (2), i.e., is invisible to userspace but
it may still be resurrected through the NS_GET_PARENT ioctl().
Currently namespace file handles allow much broader access to namespaces
than what is currently possible via (1)-(3). The reason is that
namespaces may remain pinned for completely internal reasons yet are
inaccessible to userspace.
For example, a user namespace my remain pinned by get_cred() calls to
stash the opener's credentials into file->f_cred. As it stands file
handles allow to resurrect such a users namespace even though this
should not be possible via (1)-(3). This is a fundamental uapi change
that we shouldn't do if we don't have to.
Consider the following insane case: Various architectures support the
CONFIG_MMU_LAZY_TLB_REFCOUNT option which uses lazy TLB destruction.
When this option is set a userspace task's struct mm_struct may be used
for kernel threads such as the idle task and will only be destroyed once
the cpu's runqueue switches back to another task. But because of ptrace()
permission checks struct mm_struct stashes the user namespace of the
task that struct mm_struct originally belonged to. The kernel thread
will take a reference on the struct mm_struct and thus pin it.
So on an idle system user namespaces can be persisted for arbitrary
amounts of time which also means that they can be resurrected using
namespace file handles. That makes no sense whatsoever. The problem is
of course excarabted on large systems with a huge number of cpus.
To handle this nicely we introduce an active reference count which
tracks (1)-(3). This is easy to do as all of these things are already
managed centrally. Only (1)-(3) will count towards the active reference
count and only namespaces which are active may be opened via namespace
file handles.
The problem is that namespaces may be resurrected. Which means that they
can become temporarily inactive and will be reactived some time later.
Currently the only example of this is the SIOGCSKNS socket ioctl. The
SIOCGSKNS ioctl allows to open a network namespace file descriptor based
on a socket file descriptor.
If a socket is tied to a network namespace that subsequently becomes
inactive but that socket is persisted by another process in another
network namespace (e.g., via SCM_RIGHTS of pidfd_getfd()) then the
SIOCGSKNS ioctl will resurrect this network namespace.
So calls to open_related_ns() and open_namespace() will end up
resurrecting the corresponding namespace tree.
Note that the active reference count does not regulate the lifetime of
the namespace itself. This is still done by the normal reference count.
The active reference count can only be elevated if the regular reference
count is elevated.
The active reference count also doesn't regulate the presence of a
namespace on the namespace trees. It only regulates its visiblity to
namespace file handles (and in later patches to listns()).
A namespace remains on the namespace trees from creation until its
actual destruction. This will allow the kernel to always reach any
namespace trivially and it will also enable subsystems like bpf to walk
the namespace lists on the system for tracing or general introspection
purposes.
Note that different namespaces have different visibility lifetimes on
current kernels. While most namespace are immediately released when the
last task using them exits, the user- and pid namespace are persisted
and thus both remain accessible via /proc/<pid>/ns/<ns_type>.
The user namespace lifetime is aliged with struct cred and is only
released through exit_creds(). However, it becomes inaccessible to
userspace once the last task using it is reaped, i.e., when
release_task() is called and all proc entries are flushed. Similarly,
the pid namespace is also visible until the last task using it has been
reaped and the associated pid numbers are freed.
The active reference counts of the user- and pid namespace are
decremented once the task is reaped.
Based on the namespace trees and the active reference count, a new
listns() system call that allows userspace to iterate through namespaces
in the system. This provides a programmatic interface to discover and
inspect namespaces, enhancing existing namespace apis.
Currently, there is no direct way for userspace to enumerate namespaces
in the system. Applications must resort to scanning /proc/<pid>/ns/
across all processes, which is:
1. Inefficient - requires iterating over all processes
2. Incomplete - misses inactive namespaces that aren't attached to any
running process but are kept alive by file descriptors, bind mounts,
or parent namespace references
3. Permission-heavy - requires access to /proc for many processes
4. No ordering or ownership.
5. No filtering per namespace type: Must always iterate and check all
namespaces.
The list goes on. The listns() system call solves these problems by
providing direct kernel-level enumeration of namespaces. It is similar
to listmount() but obviously tailored to namespaces.
/*
* @req: Pointer to struct ns_id_req specifying search parameters
* @ns_ids: User buffer to receive namespace IDs
* @nr_ns_ids: Size of ns_ids buffer (maximum number of IDs to return)
* @flags: Reserved for future use (must be 0)
*/
ssize_t listns(const struct ns_id_req *req, u64 *ns_ids,
size_t nr_ns_ids, unsigned int flags);
Returns:
- On success: Number of namespace IDs written to ns_ids
- On error: Negative error code
/*
* @size: Structure size
* @ns_id: Starting point for iteration; use 0 for first call, then
* use the last returned ID for subsequent calls to paginate
* @ns_type: Bitmask of namespace types to include (from enum ns_type):
* 0: Return all namespace types
* MNT_NS: Mount namespaces
* NET_NS: Network namespaces
* USER_NS: User namespaces
* etc. Can be OR'd together
* @user_ns_id: Filter results to namespaces owned by this user namespace:
* 0: Return all namespaces (subject to permission checks)
* LISTNS_CURRENT_USER: Namespaces owned by caller's user namespace
* Other value: Namespaces owned by the specified user namespace ID
*/
struct ns_id_req {
__u32 size; /* sizeof(struct ns_id_req) */
__u32 spare; /* Reserved, must be 0 */
__u64 ns_id; /* Last seen namespace ID (for pagination) */
__u32 ns_type; /* Filter by namespace type(s) */
__u32 spare2; /* Reserved, must be 0 */
__u64 user_ns_id; /* Filter by owning user namespace */
};
Example 1: List all namespaces
void list_all_namespaces(void)
{
struct ns_id_req req = {
.size = sizeof(req),
.ns_id = 0, /* Start from beginning */
.ns_type = 0, /* All types */
.user_ns_id = 0, /* All user namespaces */
};
uint64_t ids[100];
ssize_t ret;
printf("All namespaces in the system:\n");
do {
ret = listns(&req, ids, 100, 0);
if (ret < 0) {
perror("listns");
break;
}
for (ssize_t i = 0; i < ret; i++)
printf(" Namespace ID: %llu\n", (unsigned long long)ids[i]);
/* Continue from last seen ID */
if (ret > 0)
req.ns_id = ids[ret - 1];
} while (ret == 100); /* Buffer was full, more may exist */
}
printf("Enumerating all namespaces with pagination:\n");
while (1) {
ret = listns(&req, ids, 50, 0);
if (ret < 0) {
perror("listns");
break;
}
if (ret == 0)
break; /* No more namespaces */
total += ret;
printf(" Batch: %zd namespaces\n", ret);
/* Last ID in this batch becomes start of next batch */
req.ns_id = ids[ret - 1];
if (ret < 50)
break; /* Partial batch = end of results */
}
printf("Total: %zu namespaces\n", total);
}
listns() respects namespace isolation and capabilities:
(1) Global listing (user_ns_id = 0):
- Requires CAP_SYS_ADMIN in the namespace's owning user namespace
- OR the namespace must be in the caller's namespace context (e.g.,
a namespace the caller is currently using)
- User namespaces additionally allow listing if the caller has
CAP_SYS_ADMIN in that user namespace itself
(2) Owner-filtered listing (user_ns_id != 0):
- Requires CAP_SYS_ADMIN in the specified owner user namespace
- OR the namespace must be in the caller's namespace context
- This allows unprivileged processes to enumerate namespaces they own
(3) Visibility:
- Only "active" namespaces are listed
- A namespace is active if it has a non-zero __ns_ref_active count
- This includes namespaces used by running processes, held by open
file descriptors, or kept active by bind mounts
- Inactive namespaces (kept alive only by internal kernel
references) are not visible via listns()
* patches from https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-0-2e6f823ebdc0@kernel.org: (74 commits)
selftests/namespace: test listns() pagination
selftests/namespace: add stress test
selftests/namespace: commit_creds() active reference tests
selftests/namespace: third threaded active reference count test
selftests/namespace: second threaded active reference count test
selftests/namespace: first threaded active reference count test
selftests/namespaces: twelth inactive namespace resurrection test
selftests/namespaces: eleventh inactive namespace resurrection test
selftests/namespaces: tenth inactive namespace resurrection test
selftests/namespaces: ninth inactive namespace resurrection test
selftests/namespaces: eigth inactive namespace resurrection test
selftests/namespaces: seventh inactive namespace resurrection test
selftests/namespaces: sixth inactive namespace resurrection test
selftests/namespaces: fifth inactive namespace resurrection test
selftests/namespaces: fourth inactive namespace resurrection test
selftests/namespaces: third inactive namespace resurrection test
selftests/namespaces: second inactive namespace resurrection test
selftests/namespaces: first inactive namespace resurrection test
selftests/namespaces: seventh listns() permission test
selftests/namespaces: sixth listns() permission test
...
Stress tests for namespace active reference counting.
These tests validate that the active reference counting system can
handle high load scenarios including rapid namespace
creation/destruction, large numbers of concurrent namespaces, and
various edge cases under stress.
selftests/namespace: third threaded active reference count test
Test that namespaces become inactive after subprocess with multiple
threads exits. Create a subprocess that unshares user and network
namespaces, then creates two threads that share those namespaces. Verify
that after all threads and subprocess exit, the namespaces are no longer
listed by listns() and cannot be opened by open_by_handle_at().
selftests/namespace: second threaded active reference count test
Test that a namespace remains active while a thread holds an fd to it.
Even after the thread exits, the namespace should remain active as long
as another thread holds a file descriptor to it.
selftests/namespaces: twelth inactive namespace resurrection test
Test multi-level namespace resurrection across three user namespace levels.
This test creates a complex namespace hierarchy with three levels of user
namespaces and a network namespace at the deepest level. It verifies that
the resurrection semantics work correctly when SIOCGSKNS is called on a
socket from an inactive namespace tree, and that listns() and
open_by_handle_at() correctly respect visibility rules.
Hierarchy after child processes exit (all with 0 active refcount):
net_L3A (0) <- Level 3 network namespace
|
+
userns_L3 (0) <- Level 3 user namespace
|
+
userns_L2 (0) <- Level 2 user namespace
|
+
userns_L1 (0) <- Level 1 user namespace
|
x
init_user_ns
The test verifies:
1. SIOCGSKNS on a socket from inactive net_L3A resurrects the entire chain
2. After resurrection, all namespaces are visible in listns()
3. Resurrected namespaces can be reopened via file handles
4. Closing the netns FD cascades down: the entire ownership chain
(userns_L3 -> userns_L2 -> userns_L1) becomes inactive again
5. Inactive namespaces disappear from listns() and cannot be reopened
6. Calling SIOCGSKNS again on the same socket resurrects the tree again
7. After second resurrection, namespaces are visible and can be reopened
selftests/namespaces: eleventh inactive namespace resurrection test
Test combined listns() and file handle operations with socket-kept
netns. Create a netns, keep it alive with a socket, verify it appears in
listns(), then reopen it via file handle obtained from listns() entry.
selftests/namespaces: tenth inactive namespace resurrection test
Test that socket-kept netns can be reopened via file handle.
Verify that a network namespace kept alive by a socket FD can be
reopened using file handles even after the creating process exits.
selftests/namespaces: ninth inactive namespace resurrection test
Test that socket-kept netns appears in listns() output.
Verify that a network namespace kept alive by a socket FD appears in
listns() output even after the creating process exits, and that it
disappears when the socket is closed.
selftests/namespaces: second inactive namespace resurrection test
Test that socket file descriptors keep network namespaces active. Create
a network namespace, create a socket in it, then exit the namespace. The
namespace should remain active while the socket FD is held.
selftests/namespaces: third listns() permission test
Test that users cannot see namespaces from unrelated user namespaces.
Create two sibling user namespaces, verify they can't see each other's
owned namespaces.
selftests/namespaces: first listns() permission test
Test that unprivileged users can only see namespaces they're currently
in. Create a namespace, drop privileges, verify we can only see our own
namespaces.
selftests/namespaces: fourteenth active reference count tests
Test that user namespace as a child also propagates correctly.
Create user_A -> user_B, verify when user_B is active that user_A
is also active. This is different from non-user namespace children.
selftests/namespaces: thirteenth active reference count tests
Test that parent stays active as long as ANY child is active.
Create parent user namespace with two child net namespaces.
Parent should remain active until BOTH children are inactive.
selftests/namespaces: twelth active reference count tests
Test hierarchical propagation with deep namespace hierarchy.
Create: init_user_ns -> user_A -> user_B -> net_ns
When net_ns is active, both user_A and user_B should be active.
This verifies the conditional recursion in __ns_ref_active_put() works.
selftests/namespaces: seventh active reference count tests
Test hierarchical active reference propagation.
When a child namespace is active, its owning user namespace should also
be active automatically due to hierarchical active reference propagation.
This ensures parents are always reachable when children are active.
selftests/namespaces: sixth active reference count tests
Test that an open file descriptor keeps a namespace active.
Even after the creating process exits, the namespace should remain
active as long as an fd is held open.
selftests/namespaces: second active reference count tests
Test namespace lifecycle: create a namespace in a child process, get a
file handle while it's active, then try to reopen after the process
exits (namespace becomes inactive).
Add a new listns() system call that allows userspace to iterate through
namespaces in the system. This provides a programmatic interface to
discover and inspect namespaces, enhancing existing namespace apis.
Currently, there is no direct way for userspace to enumerate namespaces
in the system. Applications must resort to scanning /proc/<pid>/ns/
across all processes, which is:
1. Inefficient - requires iterating over all processes
2. Incomplete - misses inactive namespaces that aren't attached to any
running process but are kept alive by file descriptors, bind mounts,
or parent namespace references
3. Permission-heavy - requires access to /proc for many processes
4. No ordering or ownership.
5. No filtering per namespace type: Must always iterate and check all
namespaces.
The list goes on. The listns() system call solves these problems by
providing direct kernel-level enumeration of namespaces. It is similar
to listmount() but obviously tailored to namespaces.
/*
* @req: Pointer to struct ns_id_req specifying search parameters
* @ns_ids: User buffer to receive namespace IDs
* @nr_ns_ids: Size of ns_ids buffer (maximum number of IDs to return)
* @flags: Reserved for future use (must be 0)
*/
ssize_t listns(const struct ns_id_req *req, u64 *ns_ids,
size_t nr_ns_ids, unsigned int flags);
Returns:
- On success: Number of namespace IDs written to ns_ids
- On error: Negative error code
/*
* @size: Structure size
* @ns_id: Starting point for iteration; use 0 for first call, then
* use the last returned ID for subsequent calls to paginate
* @ns_type: Bitmask of namespace types to include (from enum ns_type):
* 0: Return all namespace types
* MNT_NS: Mount namespaces
* NET_NS: Network namespaces
* USER_NS: User namespaces
* etc. Can be OR'd together
* @user_ns_id: Filter results to namespaces owned by this user namespace:
* 0: Return all namespaces (subject to permission checks)
* LISTNS_CURRENT_USER: Namespaces owned by caller's user namespace
* Other value: Namespaces owned by the specified user namespace ID
*/
struct ns_id_req {
__u32 size; /* sizeof(struct ns_id_req) */
__u32 spare; /* Reserved, must be 0 */
__u64 ns_id; /* Last seen namespace ID (for pagination) */
__u32 ns_type; /* Filter by namespace type(s) */
__u32 spare2; /* Reserved, must be 0 */
__u64 user_ns_id; /* Filter by owning user namespace */
};
Example 1: List all namespaces
void list_all_namespaces(void)
{
struct ns_id_req req = {
.size = sizeof(req),
.ns_id = 0, /* Start from beginning */
.ns_type = 0, /* All types */
.user_ns_id = 0, /* All user namespaces */
};
uint64_t ids[100];
ssize_t ret;
printf("All namespaces in the system:\n");
do {
ret = listns(&req, ids, 100, 0);
if (ret < 0) {
perror("listns");
break;
}
for (ssize_t i = 0; i < ret; i++)
printf(" Namespace ID: %llu\n", (unsigned long long)ids[i]);
/* Continue from last seen ID */
if (ret > 0)
req.ns_id = ids[ret - 1];
} while (ret == 100); /* Buffer was full, more may exist */
}
printf("Enumerating all namespaces with pagination:\n");
while (1) {
ret = listns(&req, ids, 50, 0);
if (ret < 0) {
perror("listns");
break;
}
if (ret == 0)
break; /* No more namespaces */
total += ret;
printf(" Batch: %zd namespaces\n", ret);
/* Last ID in this batch becomes start of next batch */
req.ns_id = ids[ret - 1];
if (ret < 50)
break; /* Partial batch = end of results */
}
printf("Total: %zu namespaces\n", total);
}
Permission Model
listns() respects namespace isolation and capabilities:
(1) Global listing (user_ns_id = 0):
- Requires CAP_SYS_ADMIN in the namespace's owning user namespace
- OR the namespace must be in the caller's namespace context (e.g.,
a namespace the caller is currently using)
- User namespaces additionally allow listing if the caller has
CAP_SYS_ADMIN in that user namespace itself
(2) Owner-filtered listing (user_ns_id != 0):
- Requires CAP_SYS_ADMIN in the specified owner user namespace
- OR the namespace must be in the caller's namespace context
- This allows unprivileged processes to enumerate namespaces they own
(3) Visibility:
- Only "active" namespaces are listed
- A namespace is active if it has a non-zero __ns_ref_active count
- This includes namespaces used by running processes, held by open
file descriptors, or kept active by bind mounts
- Inactive namespaces (kept alive only by internal kernel
references) are not visible via listns()
The namespace tree doesn't express the ownership concept of namespace
appropriately. Maintain a list of directly owned namespaces per user
namespace. This will allow userspace and the kernel to use the listns()
system call to walk the namespace tree by owning user namespace. The
rbtree is used to find the relevant namespace entry point which allows
to continue iteration and the owner list can be used to walk the tree
completely lock free.
nstree: assign fixed ids to the initial namespaces
The initial set of namespace comes with fixed inode numbers making it
easy for userspace to identify them solely based on that information.
This has long preceeded anything here.
Similarly, let's assign fixed namespace ids for the initial namespaces.
Kill the cookie and use a sequentially increasing number. This has the
nice side-effect that the owning user namespace will always have a
namespace id that is smaller than any of it's descendant namespaces.
The namespace file handle struct nsfs_file_handle is uapi and userspace
is expressly allowed to generate file handles without going through
name_to_handle_at().
Allow userspace to generate a file handle where both the inode number
and the namespace type are zero and just pass in the unique namespace
id. The kernel uses the unified namespace tree to find the namespace and
open the file handle.
When the kernel creates a file handle via name_to_handle_at() it will
always fill in the type and the inode number allowing userspace to
retrieve core information.
The namespace tree is, among other things, currently used to support
file handles for namespaces. When a namespace is created it is placed on
the namespace trees and when it is destroyed it is removed from the
namespace trees.
While a namespace is on the namespace trees with a valid reference count
it is possible to reopen it through a namespace file handle. This is all
fine but has some issues that should be addressed.
On current kernels a namespace is visible to userspace in the
following cases:
(1) The namespace is in use by a task.
(2) The namespace is persisted through a VFS object (namespace file
descriptor or bind-mount).
Note that (2) only cares about direct persistence of the namespace
itself not indirectly via e.g., file->f_cred file references or
similar.
(3) The namespace is a hierarchical namespace type and is the parent of
a single or multiple child namespaces.
Case (3) is interesting because it is possible that a parent namespace
might not fulfill any of (1) or (2), i.e., is invisible to userspace but
it may still be resurrected through the NS_GET_PARENT ioctl().
Currently namespace file handles allow much broader access to namespaces
than what is currently possible via (1)-(3). The reason is that
namespaces may remain pinned for completely internal reasons yet are
inaccessible to userspace.
For example, a user namespace my remain pinned by get_cred() calls to
stash the opener's credentials into file->f_cred. As it stands file
handles allow to resurrect such a users namespace even though this
should not be possible via (1)-(3). This is a fundamental uapi change
that we shouldn't do if we don't have to.
Consider the following insane case: Various architectures support the
CONFIG_MMU_LAZY_TLB_REFCOUNT option which uses lazy TLB destruction.
When this option is set a userspace task's struct mm_struct may be used
for kernel threads such as the idle task and will only be destroyed once
the cpu's runqueue switches back to another task. But because of ptrace()
permission checks struct mm_struct stashes the user namespace of the
task that struct mm_struct originally belonged to. The kernel thread
will take a reference on the struct mm_struct and thus pin it.
So on an idle system user namespaces can be persisted for arbitrary
amounts of time which also means that they can be resurrected using
namespace file handles. That makes no sense whatsoever. The problem is
of course excarabted on large systems with a huge number of cpus.
To handle this nicely we introduce an active reference count which
tracks (1)-(3). This is easy to do as all of these things are already
managed centrally. Only (1)-(3) will count towards the active reference
count and only namespaces which are active may be opened via namespace
file handles.
The problem is that namespaces may be resurrected. Which means that they
can become temporarily inactive and will be reactived some time later.
Currently the only example of this is the SIOGCSKNS socket ioctl. The
SIOCGSKNS ioctl allows to open a network namespace file descriptor based
on a socket file descriptor.
If a socket is tied to a network namespace that subsequently becomes
inactive but that socket is persisted by another process in another
network namespace (e.g., via SCM_RIGHTS of pidfd_getfd()) then the
SIOCGSKNS ioctl will resurrect this network namespace.
So calls to open_related_ns() and open_namespace() will end up
resurrecting the corresponding namespace tree.
Note that the active reference count does not regulate the lifetime of
the namespace itself. This is still done by the normal reference count.
The active reference count can only be elevated if the regular reference
count is elevated.
The active reference count also doesn't regulate the presence of a
namespace on the namespace trees. It only regulates its visiblity to
namespace file handles (and in later patches to listns()).
A namespace remains on the namespace trees from creation until its
actual destruction. This will allow the kernel to always reach any
namespace trivially and it will also enable subsystems like bpf to walk
the namespace lists on the system for tracing or general introspection
purposes.
Note that different namespaces have different visibility lifetimes on
current kernels. While most namespace are immediately released when the
last task using them exits, the user- and pid namespace are persisted
and thus both remain accessible via /proc/<pid>/ns/<ns_type>.
The user namespace lifetime is aliged with struct cred and is only
released through exit_creds(). However, it becomes inaccessible to
userspace once the last task using it is reaped, i.e., when
release_task() is called and all proc entries are flushed. Similarly,
the pid namespace is also visible until the last task using it has been
reaped and the associated pid numbers are freed.
The active reference counts of the user- and pid namespace are
decremented once the task is reaped.
The current naming is very misleading as this really isn't exiting all
of the task's namespaces. It is only exiting the namespaces that hang of
off nsproxy. Reflect that in the name.
While pidfs dentries are never hashed and thus retain_dentry() will never
consider them for placing them on the LRU it isn't great to always have
to go and remember that. Raise DCACHE_DONTCACHE explicitly as a visual
marker that dentries aren't kept but freed immediately instead.
While nsfs dentries are never hashed and thus retain_dentry() will never
consider them for placing them on the LRU it isn't great to always have
to go and remember that. Raise DCACHE_DONTCACHE explicitly as a visual
marker that dentries aren't kept but freed immediately instead.
Currently nsfs uses the default inode_generic_drop() fallback which
drops the inode when it's unlinked or when it's unhashed. Since nsfs
never hashes inodes that always amounts to dropping the inode.
But that's just annoying to have to reason through every time we look at
this code. Switch to inode_just_drop() which always drops the inode
explicitly. This also aligns the behavior with pidfs which does the
same.
Linus Torvalds [Sun, 19 Oct 2025 14:59:43 +0000 (04:59 -1000)]
Merge tag 'sched_urgent_for_v6.18_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Borislav Petkov:
- Make sure the check for lost pelt idle time is done unconditionally
to have correct lost idle time accounting
- Stop the deadline server task before a CPU goes offline
* tag 'sched_urgent_for_v6.18_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/fair: Fix pelt lost idle time detection
sched/deadline: Stop dl_server before CPU goes offline
Linus Torvalds [Sun, 19 Oct 2025 14:54:08 +0000 (04:54 -1000)]
Merge tag 'perf_urgent_for_v6.18_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull perf fixes from Borislav Petkov:
- Make sure perf reporting works correctly in setups using
overlayfs or FUSE
- Move the uprobe optimization to a better location logically
* tag 'perf_urgent_for_v6.18_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf/core: Fix MMAP2 event device with backing files
perf/core: Fix MMAP event path names with backing files
perf/core: Fix address filter match with backing files
uprobe: Move arch_uprobe_optimize right after handlers execution
Linus Torvalds [Sun, 19 Oct 2025 14:41:27 +0000 (04:41 -1000)]
Merge tag 'x86_urgent_for_v6.18_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fixes from Borislav Petkov:
- Reset the why-the-system-rebooted register on AMD to avoid stale bits
remaining from previous boots
- Add a missing barrier in the TLB flushing code to prevent erroneously
not flushing a TLB generation
- Make sure cpa_flush() does not overshoot when computing the end range
of a flush region
- Fix resctrl bandwidth counting on AMD systems when the amount of
monitoring groups created exceeds the number the hardware can track
* tag 'x86_urgent_for_v6.18_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/CPU/AMD: Prevent reset reasons from being retained across reboot
x86/mm: Fix SMP ordering in switch_mm_irqs_off()
x86/mm: Fix overflow in __cpa_addr()
x86/resctrl: Fix miscount of bandwidth event when reactivating previously unavailable RMID
Linus Torvalds [Sat, 18 Oct 2025 20:05:13 +0000 (10:05 -1000)]
Merge tag 'rust-rustfmt' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux
Pull rustfmt fixes from Miguel Ojeda:
"Rust 'rustfmt' cleanup
'rustfmt', by default, formats imports in a way that is prone to
conflicts while merging and rebasing, since in some cases it condenses
several items into the same line.
Document in our guidelines that we will handle this for the moment
with the trailing empty comment workaround and make the tree
'rustfmt'-clean again"
* tag 'rust-rustfmt' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux:
rust: bitmap: fix formatting
rust: cpufreq: fix formatting
rust: alloc: employ a trailing comment to keep vertical layout
docs: rust: add section on imports formatting
Linus Torvalds [Sat, 18 Oct 2025 18:38:28 +0000 (08:38 -1000)]
Merge tag 'tpmdd-next-v6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd
Pull tpm fix from Jarkko Sakkinen:
"Correct the state transitions for ARM FF-A to match the spec and how
tpm_crb behaves on other platforms"
* tag 'tpmdd-next-v6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd:
tpm_crb: Add idle support for the Arm FF-A start method
Linus Torvalds [Sat, 18 Oct 2025 18:35:09 +0000 (08:35 -1000)]
Merge tag 'pci-v6.18-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci
Pull pci fixes from Bjorn Helgaas:
- Search for MSI Capability with correct ID to fix an MSI regression on
platforms with Cadence IP (Hans Zhang)
- Revert early bridge resource set up to fix resource assignment
failures that broke at least alpha boot and Snapdragon ath12k WiFi
(Ilpo Järvinen)
- Implement VMD .irq_startup()/.irq_shutdown() to fix IRQ issues that
caused boot crashes and broken devices below VMD (Inochi Amaoto)
- Select CONFIG_SCREEN_INFO on X86 to fix black screen on boot when
SCREEN_INFO not selected (Mario Limonciello)
* tag 'pci-v6.18-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci:
PCI/VGA: Select SCREEN_INFO on X86
PCI: vmd: Override irq_startup()/irq_shutdown() in vmd_init_dev_msi_info()
PCI: Revert early bridge resource set up
PCI: cadence: Search for MSI Capability with correct ID
Linus Torvalds [Sat, 18 Oct 2025 18:22:07 +0000 (08:22 -1000)]
Merge tag 'cxl-fixes-6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl
Pull Compute Express Link fixes from Dave Jiang:
"A small collection of CXL fixes. In addition to some misc fixes for
the CXL subsystem, a number of fixes for CXL extended linear cache
support are included to make it functional again.
- Avoid missing port component registers setup due to dport
enumeration failure
- Add check for no entries in cxl_feature_info to address accessing
invalid pointer.
- Use %pa printk format to emit resource_size_t in
validate_region_offset()
CXL extended linear cache support fixes:
- Fix setup of memory resource in cxl_acpi_set_cache_size()
- Set range param for region_res_match_cxl_range() as const
(addresses a compile warning for match_region_by_range() fix)
- Fix match_region_by_range() to use region_res_match_cxl_range()
- Subtract to find an hpa_alias0 in cxl_poison events to correct the
alias math calculation"
* tag 'cxl-fixes-6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl:
cxl/trace: Subtract to find an hpa_alias0 in cxl_poison events
cxl/region: Use %pa printk format to emit resource_size_t
cxl: Fix match_region_by_range() to use region_res_match_cxl_range()
cxl: Set range param for region_res_match_cxl_range() as const
cxl/acpi: Fix setup of memory resource in cxl_acpi_set_cache_size()
cxl/features: Add check for no entries in cxl_feature_info
cxl/port: Avoid missing port component registers setup
Linus Torvalds [Sat, 18 Oct 2025 18:00:43 +0000 (08:00 -1000)]
Merge tag 'bpf-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf
Pull bpf fixes from Alexei Starovoitov:
- Replace bpf_map_kmalloc_node() with kmalloc_nolock() to fix kmemleak
imbalance in tracking of bpf_async_cb structures (Alexei Starovoitov)
- Make selftests/bpf arg_parsing.c more robust to errors (Andrii
Nakryiko)
- Fix redefinition of 'off' as different kind of symbol when I40E
driver is builtin (Brahmajit Das)
- Do not disable preemption in bpf_test_run (Sahil Chandna)
- Fix memory leak in __lookup_instance error path (Shardul Bankar)
- Ensure test data is flushed to disk before reading it (Xing Guo)
* tag 'bpf-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
selftests/bpf: Fix redefinition of 'off' as different kind of symbol
bpf: Do not disable preemption in bpf_test_run().
bpf: Fix memory leak in __lookup_instance error path
selftests: arg_parsing: Ensure data is flushed to disk before reading.
bpf: Replace bpf_map_kmalloc_node() with kmalloc_nolock() to allocate bpf_async_cb structures.
selftests/bpf: make arg_parsing.c more robust to crashes
bpf: test_run: Fix ctx leak in bpf_prog_test_run_xdp error path
Linus Torvalds [Sat, 18 Oct 2025 17:23:59 +0000 (07:23 -1000)]
Merge tag 'exfat-for-6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat
Pull exfat fixes from Namjae Jeon:
- Fix out-of-bounds in FS_IOC_SETFSLABEL
- Add validation for stream entry size to prevent infinite loop
* tag 'exfat-for-6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat:
exfat: fix out-of-bounds in exfat_nls_to_ucs2()
exfat: fix improper check of dentry.stream.valid_size
Linus Torvalds [Sat, 18 Oct 2025 17:18:48 +0000 (07:18 -1000)]
Merge tag 'nfs-for-6.18-2' of git://git.linux-nfs.org/projects/anna/linux-nfs
Pull NFS client fixes from Anna Schumaker:
- Fix for FlexFiles mirror->dss allocation
- Apply delay_retrans to async operations
- Check if suid/sgid is cleared after a write when needed
- Fix setting the state renewal timer for early mounts after a reboot
* tag 'nfs-for-6.18-2' of git://git.linux-nfs.org/projects/anna/linux-nfs:
NFS4: Fix state renewals missing after boot
NFS: check if suid/sgid was cleared after a write as needed
NFS4: Apply delay_retrans to async operations
NFSv4/flexfiles: fix to allocate mirror->dss before use
Linus Torvalds [Sat, 18 Oct 2025 17:11:32 +0000 (07:11 -1000)]
Merge tag '6.18-rc1-smb-client-fixes' of git://git.samba.org/sfrench/cifs-2.6
Pull smb client fixes from Steve French:
"smb client fixes, security and smbdirect improvements, and some minor cleanup:
- Important OOB DFS fix
- Fix various potential tcon refcount leaks
- smbdirect (RDMA) fixes (following up from test event a few weeks
ago):
- Fixes to improve and simplify handling of memory lifetime of
smbdirect_mr_io structures, when a connection gets disconnected
- Make sure we really wait to reach SMBDIRECT_SOCKET_DISCONNECTED
before destroying resources
- Make sure the send/recv submission/completion queues are large
enough to avoid ib_post_send() from failing under pressure
- convert cifs.ko to use the recommended crypto libraries (instead of
crypto_shash), this also can improve performance
- Three small cleanup patches"
* tag '6.18-rc1-smb-client-fixes' of git://git.samba.org/sfrench/cifs-2.6: (24 commits)
smb: client: Consolidate cmac(aes) shash allocation
smb: client: Remove obsolete crypto_shash allocations
smb: client: Use HMAC-MD5 library for NTLMv2
smb: client: Use MD5 library for SMB1 signature calculation
smb: client: Use MD5 library for M-F symlink hashing
smb: client: Use HMAC-SHA256 library for SMB2 signature calculation
smb: client: Use HMAC-SHA256 library for key generation
smb: client: Use SHA-512 library for SMB3.1.1 preauth hash
cifs: parse_dfs_referrals: prevent oob on malformed input
smb: client: Fix refcount leak for cifs_sb_tlink
smb: client: let smbd_destroy() wait for SMBDIRECT_SOCKET_DISCONNECTED
smb: move some duplicate definitions to common/cifsglob.h
smb: client: let destroy_mr_list() keep smbdirect_mr_io memory if registered
smb: client: let destroy_mr_list() call ib_dereg_mr() before ib_dma_unmap_sg()
smb: client: call ib_dma_unmap_sg if mr->sgt.nents is not 0
smb: client: improve logic in smbd_deregister_mr()
smb: client: improve logic in smbd_register_mr()
smb: client: improve logic in allocate_mr_list()
smb: client: let destroy_mr_list() remove locked from the list
smb: client: let destroy_mr_list() call list_del(&mr->list)
...
Linus Torvalds [Sat, 18 Oct 2025 17:07:14 +0000 (07:07 -1000)]
Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
Pull kvm fixes from Paolo Bonzini:
"ARM:
- Fix the handling of ZCR_EL2 in NV VMs
- Pick the correct translation regime when doing a PTW on the back of
a SEA
- Prevent userspace from injecting an event into a vcpu that isn't
initialised yet
- Move timer save/restore to the sysreg handling code, fixing EL2
timer access in the process
- Add FGT-based trapping of MDSCR_EL1 to reduce the overhead of debug
- Fix trapping configuration when the host isn't GICv3
- Improve the detection of HCR_EL2.E2H being RES1
- Drop a spurious 'break' statement in the S1 PTW
- Don't try to access SPE when owned by EL3
Documentation updates:
- Document the failure modes of event injection
- Document that a GICv3 guest can be created on a GICv5 host with
FEAT_GCIE_LEGACY
Selftest improvements:
- Add a selftest for the effective value of HCR_EL2.AMO
- Address build warning in the timer selftest when building with
clang
- Teach irqfd selftests about non-x86 architectures
- Add missing sysregs to the set_id_regs selftest
- Fix vcpu allocation in the vgic_lpi_stress selftest
- Correctly enable interrupts in the vgic_lpi_stress selftest
x86:
- Expand the KVM_PRE_FAULT_MEMORY selftest to add a regression test
for the bug fixed by commit 3ccbf6f47098 ("KVM: x86/mmu: Return
-EAGAIN if userspace deletes/moves memslot during prefault")
- Don't try to get PMU capabilities from perf when running a CPU with
hybrid CPUs/PMUs, as perf will rightly WARN.
guest_memfd:
- Rework KVM_CAP_GUEST_MEMFD_MMAP (newly introduced in 6.18) into a
more generic KVM_CAP_GUEST_MEMFD_FLAGS
- Add a guest_memfd INIT_SHARED flag and require userspace to
explicitly set said flag to initialize memory as SHARED,
irrespective of MMAP.
The behavior merged in 6.18 is that enabling mmap() implicitly
initializes memory as SHARED, which would result in an ABI
collision for x86 CoCo VMs as their memory is currently always
initialized PRIVATE.
- Allow mmap() on guest_memfd for x86 CoCo VMs, i.e. on VMs with
private memory, to enable testing such setups, i.e. to hopefully
flush out any other lurking ABI issues before 6.18 is officially
released.
- Add testcases to the guest_memfd selftest to cover guest_memfd
without MMAP, and host userspace accesses to mmap()'d private
memory"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (46 commits)
arm64: Revamp HCR_EL2.E2H RES1 detection
KVM: arm64: nv: Use FGT write trap of MDSCR_EL1 when available
KVM: arm64: Compute per-vCPU FGTs at vcpu_load()
KVM: arm64: selftests: Fix misleading comment about virtual timer encoding
KVM: arm64: selftests: Add an E2H=0-specific configuration to get_reg_list
KVM: arm64: selftests: Make dependencies on VHE-specific registers explicit
KVM: arm64: Kill leftovers of ad-hoc timer userspace access
KVM: arm64: Fix WFxT handling of nested virt
KVM: arm64: Move CNT*CT_EL0 userspace accessors to generic infrastructure
KVM: arm64: Move CNT*_CVAL_EL0 userspace accessors to generic infrastructure
KVM: arm64: Move CNT*_CTL_EL0 userspace accessors to generic infrastructure
KVM: arm64: Add timer UAPI workaround to sysreg infrastructure
KVM: arm64: Make timer_set_offset() generally accessible
KVM: arm64: Replace timer context vcpu pointer with timer_id
KVM: arm64: Introduce timer_context_to_vcpu() helper
KVM: arm64: Hide CNTHV_*_EL2 from userspace for nVHE guests
Documentation: KVM: Update GICv3 docs for GICv5 hosts
KVM: arm64: gic-v3: Only set ICH_HCR traps for v2-on-v3 or v3 guests
KVM: arm64: selftests: Actually enable IRQs in vgic_lpi_stress
KVM: arm64: selftests: Allocate vcpus with correct size
...
Linus Torvalds [Sat, 18 Oct 2025 17:02:28 +0000 (07:02 -1000)]
Merge tag 'powerpc-6.18-2' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc fixes from Madhavan Srinivasan:
- Fix to handle NULL pointer dereference at irq domain teardown
- Fix for handling extraction of struct xive_irq_data
- Fix to skip parameter area allocation when fadump disabled
Thanks to Ganesh Goudar, Hari Bathini, Nam Cao, Ritesh Harjani (IBM),
Sourabh Jain, and Venkat Rao Bagalkote,
* tag 'powerpc-6.18-2' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
powerpc/fadump: skip parameter area allocation when fadump is disabled
powerpc, ocxl: Fix extraction of struct xive_irq_data
powerpc/pseries/msi: Fix NULL pointer dereference at irq domain teardown
Linus Torvalds [Sat, 18 Oct 2025 16:59:25 +0000 (06:59 -1000)]
Merge tag 'slab-for-6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab
Pull slab fixes from Vlastimil Babka:
- Fixes for two bugs that can be triggered when debugging options are
enabled (Hao Ge, Vlastimil Babka)
* tag 'slab-for-6.18-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab:
slab: reset slab->obj_ext when freeing and it is OBJEXTS_ALLOC_FAIL
slab: fix clearing freelist in free_deferred_objects()
projects / thirdparty / linux.git / log
