nsfs: tighten permission checks for ns iteration ioctls

Even privileged services should not necessarily be able to see other
privileged service's namespaces so they can't leak information to each
other. Use may_see_all_namespaces() helper that centralizes this policy
until the nstree adapts.

Link: https://patch.msgid.link/20260226-work-visibility-fixes-v1-1-d2c2853313bd@kernel.org
Fixes: a1d220d9dafa ("nsfs: iterate through mount namespaces")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@kernel.org # v6.12+
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/nsfs.c b/fs/nsfs.c
index db91de2086456bb9fe0547be7dbbd2de87c97ca7..be36c10c38cf81a2862c3d44f4a29e474a350eff 100644 (file)
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -199,6 +199,17 @@ static bool nsfs_ioctl_valid(unsigned int cmd)
        return false;
 }
 
+static bool may_use_nsfs_ioctl(unsigned int cmd)
+{
+       switch (_IOC_NR(cmd)) {
+       case _IOC_NR(NS_MNT_GET_NEXT):
+               fallthrough;
+       case _IOC_NR(NS_MNT_GET_PREV):
+               return may_see_all_namespaces();
+       }
+       return true;
+}
+
 static long ns_ioctl(struct file *filp, unsigned int ioctl,
                        unsigned long arg)
 {
@@ -214,6 +225,8 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
 
        if (!nsfs_ioctl_valid(ioctl))
                return -ENOIOCTLCMD;
+       if (!may_use_nsfs_ioctl(ioctl))
+               return -EPERM;
 
        ns = get_proc_ns(file_inode(filp));
        switch (ioctl) {

diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index 825f5865bfc5aeef9f3343380e64d8c18749d2c7..c8e227a3f9e22b14d83cc90fd433ad3c15544ac9 100644 (file)
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -55,6 +55,8 @@ static __always_inline bool is_ns_init_id(const struct ns_common *ns)
 
 #define ns_common_free(__ns) __ns_common_free(to_ns_common((__ns)))
 
+bool may_see_all_namespaces(void);
+
 static __always_inline __must_check int __ns_ref_active_read(const struct ns_common *ns)
 {
        return atomic_read(&ns->__ns_ref_active);

diff --git a/kernel/nscommon.c b/kernel/nscommon.c
index bdc3c86231d38e0c46e6c9b118a83256bcb332d0..3166c1fd844afd6141f0042e1455604693872da5 100644 (file)
--- a/kernel/nscommon.c
+++ b/kernel/nscommon.c
@@ -309,3 +309,9 @@ void __ns_ref_active_get(struct ns_common *ns)
                        return;
        }
 }
+
+bool may_see_all_namespaces(void)
+{
+       return (task_active_pid_ns(current) == &init_pid_ns) &&
+              ns_capable_noaudit(init_pid_ns.user_ns, CAP_SYS_ADMIN);
+}