namespace: check the mounts before reading their parents in pivot_root()

Summary

In the Linux kernel, the following vulnerability has been resolved: namespace: check the mounts before reading their parents in pivot_root() path_pivot_root() reads the parents of new_root and of the caller's root and checks whether they are shared before it checks that either mount is in the caller's mount namespace. Only namespace_sem is held. That's fine for a mount that is in the caller's mount namespace. But new_root can be a file descriptor to a mount that has been unmounted and that only the file descriptor keeps alive. If that mount stayed attached to its parent when it was unmounted nothing pins the parent for it. The final mntput() of the parent unhooks the children under mount_lock alone and frees the parent afterwards: pivot_root() close(fd), last ref on the parent ------------ --------------------------------- ex_parent = new_mnt->mnt_parent mntput_no_expire_slowpath() __umount_mnt(new_mnt) cleanup_mnt() call_rcu() IS_MNT_SHARED(ex_parent) BUG: KASAN: slab-use-after-free in path_pivot_root+0xf1a/0x1840 Read of size 4 at addr ffff8881047382f8 by task pivot_widen/157 path_pivot_root+0xf1a/0x1840 __x64_sys_pivot_root+0x165/0x190 The same goes for the caller's root via chroot(). Both outcomes of the check end in EINVAL so nothing but the read itself goes wrong. It's the same thing commit bb4609405752 ("statmount: read the parent of an unmounted mount under mount_lock") fixed for statmount(). Check that both mounts are in the caller's namespace before their parents are read. Every path returns EINVAL either way.

Timeline

1. Oct 23, 2026, 12:20 PM UTCCVE published
2. Oct 23, 2026, 12:45 PM UTCFirst seen by cve.now

Affected versions

• Linux Linux

  From e0c9c0afd2fc958ffa34b697972721d81df8a56f · fixed in a56d4f8f8f4c5d9ac339d5c03a9d90eecd3697fc; From e0c9c0afd2fc958ffa34b697972721d81df8a56f · fixed in 3c2441e21c3df867e4131e0ff784ecdb3a7a55f8; From e0c9c0afd2fc958ffa34b697972721d81df8a56f · fixed in e3aba6900483f64e6c9eb328150dd633b7d36c1c; From e0c9c0afd2fc958ffa34b697972721d81df8a56f · fixed in 3dad2330c89343ba083cf7868779083fd5fbe0fe; From e0c9c0afd2fc958ffa34b697972721d81df8a56f · fixed in 6b7c001eb5857fa09041f47673666060a2e5fc1c; From 4.0.2 · fixed in 4.1

• Linux Linux

  4.1

• KernelLinux

  From 4.1.0 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.2.11

References 5