binfmt_misc: don't warn when the mount is completed from another user namespace

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74618
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-22 16:16:34 UTC
Updated2026-08-22 16:16:34 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: binfmt_misc: don't warn when the mount is completed from another user namespace fsopen() records the caller's user namespace in fc->user_ns and hands back an ordinary file descriptor. Nothing ties the task that calls fsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The fd is inherited across fork() and exec() and it can be passed over a unix socket. Completing a context from another user namespace is allowed on purpose. vfs_cmd_create() authorizes the create with mount_capable(), which for FS_USERNS_MOUNT checks ns_capable(fc->user_ns, CAP_SYS_ADMIN), and that succeeds for a task holding CAP_SYS_ADMIN in an ancestor of fc->user_ns. So an unprivileged task can reach the WARN_ON() in bm_fill_super(): create a user and a mount namespace in a child, call fsopen("binfmt_misc") there, send the fscontext fd to the parent and let the parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no capability is needed anywhere: WARNING: fs/binfmt_misc.c:938 at bm_fill_super+0xa2/0xc0 [binfmt_misc] CPU: 15 UID: 1000 PID: 3243382 Comm: fswarn Call Trace: get_tree_keyed+0x7d/0xb0 bm_get_tree+0x34/0x90 [binfmt_misc] vfs_get_tree+0x2a/0x100 vfs_cmd_create+0x60/0xf0 __do_sys_fsconfig+0x4b2/0x500 The child needs the mount namespace because fsopen() itself gates on may_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning the caller's mount namespace. fsconfig() doesn't repeat that check. It is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be raised in a loop to taint the kernel and flood the log, and it panics a kernel booted with panic_on_warn. Keep refusing the mount and stop warning about it. Nothing in bm_fill_super() depends on the two namespaces matching, it derives everything from sb->s_user_ns.

Risk And Classification

EPSS: 0.001680000 probability, percentile 0.062050000 (date 2026-08-24)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 21ca59b365c091d583f36ac753eaa8baf947be6f 37cf5cf1320a84a17225a1690547b8a0812ca94e git Not specified
CNA Linux Linux affected 21ca59b365c091d583f36ac753eaa8baf947be6f 24e95a24f151ce40d5fc1b3a6cefbcda8ded736c git Not specified
CNA Linux Linux affected 21ca59b365c091d583f36ac753eaa8baf947be6f 047f927f54c6c17593e93aafe82dcb7acdda2a71 git Not specified
CNA Linux Linux affected 21ca59b365c091d583f36ac753eaa8baf947be6f 79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6 git Not specified
CNA Linux Linux affected 6.7 Not specified
CNA Linux Linux unaffected 6.7 semver Not specified
CNA Linux Linux unaffected 6.12.104 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.45 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.9 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/24e95a24f151ce40d5fc1b3a6cefbcda8ded736c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/047f927f54c6c17593e93aafe82dcb7acdda2a71 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/37cf5cf1320a84a17225a1690547b8a0812ca94e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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