--- /dev/null
+From 85b6d24646e4125c591639841169baa98a2da503 Mon Sep 17 00:00:00 2001
+From: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
+Date: Fri, 19 Nov 2021 16:43:21 -0800
+Subject: shm: extend forced shm destroy to support objects from several IPC nses
+
+From: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
+
+commit 85b6d24646e4125c591639841169baa98a2da503 upstream.
+
+Currently, the exit_shm() function not designed to work properly when
+task->sysvshm.shm_clist holds shm objects from different IPC namespaces.
+
+This is a real pain when sysctl kernel.shm_rmid_forced = 1, because it
+leads to use-after-free (reproducer exists).
+
+This is an attempt to fix the problem by extending exit_shm mechanism to
+handle shm's destroy from several IPC ns'es.
+
+To achieve that we do several things:
+
+1. add a namespace (non-refcounted) pointer to the struct shmid_kernel
+
+2. during new shm object creation (newseg()/shmget syscall) we
+ initialize this pointer by current task IPC ns
+
+3. exit_shm() fully reworked such that it traverses over all shp's in
+ task->sysvshm.shm_clist and gets IPC namespace not from current task
+ as it was before but from shp's object itself, then call
+ shm_destroy(shp, ns).
+
+Note: We need to be really careful here, because as it was said before
+(1), our pointer to IPC ns non-refcnt'ed. To be on the safe side we
+using special helper get_ipc_ns_not_zero() which allows to get IPC ns
+refcounter only if IPC ns not in the "state of destruction".
+
+Q/A
+
+Q: Why can we access shp->ns memory using non-refcounted pointer?
+A: Because shp object lifetime is always shorther than IPC namespace
+ lifetime, so, if we get shp object from the task->sysvshm.shm_clist
+ while holding task_lock(task) nobody can steal our namespace.
+
+Q: Does this patch change semantics of unshare/setns/clone syscalls?
+A: No. It's just fixes non-covered case when process may leave IPC
+ namespace without getting task->sysvshm.shm_clist list cleaned up.
+
+Link: https://lkml.kernel.org/r/67bb03e5-f79c-1815-e2bf-949c67047418@colorfullife.com
+Link: https://lkml.kernel.org/r/20211109151501.4921-1-manfred@colorfullife.com
+Fixes: ab602f79915 ("shm: make exit_shm work proportional to task activity")
+Co-developed-by: Manfred Spraul <manfred@colorfullife.com>
+Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
+Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
+Cc: "Eric W. Biederman" <ebiederm@xmission.com>
+Cc: Davidlohr Bueso <dave@stgolabs.net>
+Cc: Greg KH <gregkh@linuxfoundation.org>
+Cc: Andrei Vagin <avagin@gmail.com>
+Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
+Cc: Vasily Averin <vvs@virtuozzo.com>
+Cc: <stable@vger.kernel.org>
+Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ include/linux/ipc_namespace.h | 15 +++
+ include/linux/sched.h | 2
+ include/linux/shm.h | 13 ++-
+ ipc/shm.c | 176 +++++++++++++++++++++++++++++++-----------
+ 4 files changed, 159 insertions(+), 47 deletions(-)
+
+--- a/include/linux/ipc_namespace.h
++++ b/include/linux/ipc_namespace.h
+@@ -123,6 +123,16 @@ static inline struct ipc_namespace *get_
+ return ns;
+ }
+
++static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns)
++{
++ if (ns) {
++ if (atomic_inc_not_zero(&ns->count))
++ return ns;
++ }
++
++ return NULL;
++}
++
+ extern void put_ipc_ns(struct ipc_namespace *ns);
+ #else
+ static inline struct ipc_namespace *copy_ipcs(unsigned long flags,
+@@ -138,6 +148,11 @@ static inline struct ipc_namespace *get_
+ {
+ return ns;
+ }
++
++static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns)
++{
++ return ns;
++}
+
+ static inline void put_ipc_ns(struct ipc_namespace *ns)
+ {
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -2792,7 +2792,7 @@ static inline int thread_group_empty(str
+ * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
+ * subscriptions and synchronises with wait4(). Also used in procfs. Also
+ * pins the final release of task.io_context. Also protects ->cpuset and
+- * ->cgroup.subsys[]. And ->vfork_done.
++ * ->cgroup.subsys[]. And ->vfork_done. And ->sysvshm.shm_clist.
+ *
+ * Nests both inside and outside of read_lock(&tasklist_lock).
+ * It must not be nested with write_lock_irq(&tasklist_lock),
+--- a/include/linux/shm.h
++++ b/include/linux/shm.h
+@@ -19,9 +19,18 @@ struct shmid_kernel /* private to the ke
+ pid_t shm_lprid;
+ struct user_struct *mlock_user;
+
+- /* The task created the shm object. NULL if the task is dead. */
++ /*
++ * The task created the shm object, for
++ * task_lock(shp->shm_creator)
++ */
+ struct task_struct *shm_creator;
+- struct list_head shm_clist; /* list by creator */
++
++ /*
++ * List by creator. task_lock(->shm_creator) required for read/write.
++ * If list_empty(), then the creator is dead already.
++ */
++ struct list_head shm_clist;
++ struct ipc_namespace *ns;
+ };
+
+ /* shm_mode upper byte flags */
+--- a/ipc/shm.c
++++ b/ipc/shm.c
+@@ -90,6 +90,7 @@ static void do_shm_rmid(struct ipc_names
+ {
+ struct shmid_kernel *shp;
+ shp = container_of(ipcp, struct shmid_kernel, shm_perm);
++ WARN_ON(ns != shp->ns);
+
+ if (shp->shm_nattch) {
+ shp->shm_perm.mode |= SHM_DEST;
+@@ -180,10 +181,43 @@ static void shm_rcu_free(struct rcu_head
+ ipc_rcu_free(head);
+ }
+
+-static inline void shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *s)
++/*
++ * It has to be called with shp locked.
++ * It must be called before ipc_rmid()
++ */
++static inline void shm_clist_rm(struct shmid_kernel *shp)
++{
++ struct task_struct *creator;
++
++ /* ensure that shm_creator does not disappear */
++ rcu_read_lock();
++
++ /*
++ * A concurrent exit_shm may do a list_del_init() as well.
++ * Just do nothing if exit_shm already did the work
++ */
++ if (!list_empty(&shp->shm_clist)) {
++ /*
++ * shp->shm_creator is guaranteed to be valid *only*
++ * if shp->shm_clist is not empty.
++ */
++ creator = shp->shm_creator;
++
++ task_lock(creator);
++ /*
++ * list_del_init() is a nop if the entry was already removed
++ * from the list.
++ */
++ list_del_init(&shp->shm_clist);
++ task_unlock(creator);
++ }
++ rcu_read_unlock();
++}
++
++static inline void shm_rmid(struct shmid_kernel *s)
+ {
+- list_del(&s->shm_clist);
+- ipc_rmid(&shm_ids(ns), &s->shm_perm);
++ shm_clist_rm(s);
++ ipc_rmid(&shm_ids(s->ns), &s->shm_perm);
+ }
+
+
+@@ -238,7 +272,7 @@ static void shm_destroy(struct ipc_names
+ shm_file = shp->shm_file;
+ shp->shm_file = NULL;
+ ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
+- shm_rmid(ns, shp);
++ shm_rmid(shp);
+ shm_unlock(shp);
+ if (!is_file_hugepages(shm_file))
+ shmem_lock(shm_file, 0, shp->mlock_user);
+@@ -259,10 +293,10 @@ static void shm_destroy(struct ipc_names
+ *
+ * 2) sysctl kernel.shm_rmid_forced is set to 1.
+ */
+-static bool shm_may_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
++static bool shm_may_destroy(struct shmid_kernel *shp)
+ {
+ return (shp->shm_nattch == 0) &&
+- (ns->shm_rmid_forced ||
++ (shp->ns->shm_rmid_forced ||
+ (shp->shm_perm.mode & SHM_DEST));
+ }
+
+@@ -293,7 +327,7 @@ static void shm_close(struct vm_area_str
+ shp->shm_lprid = task_tgid_vnr(current);
+ shp->shm_dtim = get_seconds();
+ shp->shm_nattch--;
+- if (shm_may_destroy(ns, shp))
++ if (shm_may_destroy(shp))
+ shm_destroy(ns, shp);
+ else
+ shm_unlock(shp);
+@@ -314,10 +348,10 @@ static int shm_try_destroy_orphaned(int
+ *
+ * As shp->* are changed under rwsem, it's safe to skip shp locking.
+ */
+- if (shp->shm_creator != NULL)
++ if (!list_empty(&shp->shm_clist))
+ return 0;
+
+- if (shm_may_destroy(ns, shp)) {
++ if (shm_may_destroy(shp)) {
+ shm_lock_by_ptr(shp);
+ shm_destroy(ns, shp);
+ }
+@@ -335,48 +369,97 @@ void shm_destroy_orphaned(struct ipc_nam
+ /* Locking assumes this will only be called with task == current */
+ void exit_shm(struct task_struct *task)
+ {
+- struct ipc_namespace *ns = task->nsproxy->ipc_ns;
+- struct shmid_kernel *shp, *n;
++ for (;;) {
++ struct shmid_kernel *shp;
++ struct ipc_namespace *ns;
+
+- if (list_empty(&task->sysvshm.shm_clist))
+- return;
++ task_lock(task);
++
++ if (list_empty(&task->sysvshm.shm_clist)) {
++ task_unlock(task);
++ break;
++ }
++
++ shp = list_first_entry(&task->sysvshm.shm_clist, struct shmid_kernel,
++ shm_clist);
+
+- /*
+- * If kernel.shm_rmid_forced is not set then only keep track of
+- * which shmids are orphaned, so that a later set of the sysctl
+- * can clean them up.
+- */
+- if (!ns->shm_rmid_forced) {
+- down_read(&shm_ids(ns).rwsem);
+- list_for_each_entry(shp, &task->sysvshm.shm_clist, shm_clist)
+- shp->shm_creator = NULL;
+ /*
+- * Only under read lock but we are only called on current
+- * so no entry on the list will be shared.
++ * 1) Get pointer to the ipc namespace. It is worth to say
++ * that this pointer is guaranteed to be valid because
++ * shp lifetime is always shorter than namespace lifetime
++ * in which shp lives.
++ * We taken task_lock it means that shp won't be freed.
+ */
+- list_del(&task->sysvshm.shm_clist);
+- up_read(&shm_ids(ns).rwsem);
+- return;
+- }
++ ns = shp->ns;
+
+- /*
+- * Destroy all already created segments, that were not yet mapped,
+- * and mark any mapped as orphan to cover the sysctl toggling.
+- * Destroy is skipped if shm_may_destroy() returns false.
+- */
+- down_write(&shm_ids(ns).rwsem);
+- list_for_each_entry_safe(shp, n, &task->sysvshm.shm_clist, shm_clist) {
+- shp->shm_creator = NULL;
++ /*
++ * 2) If kernel.shm_rmid_forced is not set then only keep track of
++ * which shmids are orphaned, so that a later set of the sysctl
++ * can clean them up.
++ */
++ if (!ns->shm_rmid_forced)
++ goto unlink_continue;
+
+- if (shm_may_destroy(ns, shp)) {
+- shm_lock_by_ptr(shp);
+- shm_destroy(ns, shp);
++ /*
++ * 3) get a reference to the namespace.
++ * The refcount could be already 0. If it is 0, then
++ * the shm objects will be free by free_ipc_work().
++ */
++ ns = get_ipc_ns_not_zero(ns);
++ if (!ns) {
++unlink_continue:
++ list_del_init(&shp->shm_clist);
++ task_unlock(task);
++ continue;
+ }
+- }
+
+- /* Remove the list head from any segments still attached. */
+- list_del(&task->sysvshm.shm_clist);
+- up_write(&shm_ids(ns).rwsem);
++ /*
++ * 4) get a reference to shp.
++ * This cannot fail: shm_clist_rm() is called before
++ * ipc_rmid(), thus the refcount cannot be 0.
++ */
++ WARN_ON(!ipc_rcu_getref(&shp->shm_perm));
++
++ /*
++ * 5) unlink the shm segment from the list of segments
++ * created by current.
++ * This must be done last. After unlinking,
++ * only the refcounts obtained above prevent IPC_RMID
++ * from destroying the segment or the namespace.
++ */
++ list_del_init(&shp->shm_clist);
++
++ task_unlock(task);
++
++ /*
++ * 6) we have all references
++ * Thus lock & if needed destroy shp.
++ */
++ down_write(&shm_ids(ns).rwsem);
++ shm_lock_by_ptr(shp);
++ /*
++ * rcu_read_lock was implicitly taken in shm_lock_by_ptr, it's
++ * safe to call ipc_rcu_putref here
++ */
++ ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
++
++ if (ipc_valid_object(&shp->shm_perm)) {
++ if (shm_may_destroy(shp))
++ shm_destroy(ns, shp);
++ else
++ shm_unlock(shp);
++ } else {
++ /*
++ * Someone else deleted the shp from namespace
++ * idr/kht while we have waited.
++ * Just unlock and continue.
++ */
++ shm_unlock(shp);
++ }
++
++ up_write(&shm_ids(ns).rwsem);
++ put_ipc_ns(ns); /* paired with get_ipc_ns_not_zero */
++ }
+ }
+
+ static int shm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+@@ -607,7 +690,11 @@ static int newseg(struct ipc_namespace *
+ goto no_id;
+ }
+
++ shp->ns = ns;
++
++ task_lock(current);
+ list_add(&shp->shm_clist, ¤t->sysvshm.shm_clist);
++ task_unlock(current);
+
+ /*
+ * shmid gets reported as "inode#" in /proc/pid/maps.
+@@ -1252,7 +1339,8 @@ out_nattch:
+ down_write(&shm_ids(ns).rwsem);
+ shp = shm_lock(ns, shmid);
+ shp->shm_nattch--;
+- if (shm_may_destroy(ns, shp))
++
++ if (shm_may_destroy(shp))
+ shm_destroy(ns, shp);
+ else
+ shm_unlock(shp);
projects / thirdparty / kernel / stable-queue.git / commitdiff
