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fkie_cve-2026-98977

In the Linux kernel, the following vulnerability has been resolved:

namespace: handle mount locking for automounts correctly

If mounts are propagated across user namespaces, attach_recursive_mnt() locks every copy of the source mount to protect overmounts from vanishing and revealing the underlying files or directories.

The user namespace is taken from the caller's mount namespaces since this is where the mounts end up. Except, that's not always true. Automounts may legitimately get popped in by tasks located in a different mount and user namespace during path lookup.

Then check doesn't make sense at that point. The copy in the namespace of the parent - which may be the host's - is now locked and the host cannot change the flags of its own mounts anymore.

Here's the reproducer:

- host has debugfs mounted nosuid,nodev,noexec and shared - tracefs automount below it is not yet active - hand a child process a directory descriptor on that mount - child process enters auser and mount namespace - child process' namespace now holds a locked copy of the host's debugfs mount that receives propagation from it - child process stats "tracing/." through the descriptor - lookup runs on the host's mount so the automount lands below the host's mount - propagation puts a copy below the child's copy - both try to clear the flags on the mount they got, with a bind remount:

host, on its own automount: MS_REMOUNT|MS_BIND = EPERM child, on the copy in its namespace: M…

GHSA-qrj7-g2h3-853j

In the Linux kernel, the following vulnerability has been resolved:

namespace: handle mount locking for automounts correctly

If mounts are propagated across user namespaces, attach_recursive_mnt() locks every copy of the source mount to protect overmounts from vanishing and revealing the underlying files or directories.

Then check doesn't make sense at that point. The copy in the namespace of the parent - which may be the host's - is now locked and the host cannot change the flags of its own mounts anymore.

Here's the reproducer:

host, on its own automount: MS_REMOUNT|MS_BIND = EPERM child, on the copy in its namespace: M…

msrc_CVE-2026-98977 — namespace: handle mount locking for automounts correctly

msrc_CVE-2026-98977