__legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock

Summary

In the Linux kernel, the following vulnerability has been resolved: __legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock ... or we risk stealing final mntput from sync umount - raising mnt_count after umount(2) has verified that victim is not busy, but before it has set MNT_SYNC_UMOUNT; in that case __legitimize_mnt() doesn't see that it's safe to quietly undo mnt_count increment and leaves dropping the reference to caller, where it'll be a full-blown mntput(). Check under mount_lock is needed; leaving the current one done before taking that makes no sense - it's nowhere near common enough to bother with.

Timeline

1. Jun 18, 2025, 9:33 AM UTCCVE published
2. Oct 15, 2026, 9:46 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 15, 2026, 9:52 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in 628fb00195ce21a90cf9e4e3d105cd9e58f77b40; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in b89eb56a378b7b2c1176787fc228d0a57172bdd5; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in f6d45fd92f62845cbd1eb5128fd8f0ed7d0c5a42; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in 9b0915e72b3cf52474dcee0b24a2f99d93e604a3; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in d8ece4ced3b051e656c77180df2e69e19e24edc1; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in 8cafd7266fa02e0863bacbf872fe635c0b9725eb; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in b55996939c71a3e1a38f3cdc6a8859797efc9083; From 48a066e72d970a3e225a9c18690d570c736fc455 · fixed in 250cf3693060a5f803c5f1ddc082bb06b16112a9

• Linux Linux

  3.13

• KernelLinux

  From 3.13.0 · fixed in 5.4.294; From 5.5.0 · fixed in 5.10.238; From 5.11.0 · fixed in 5.15.185; From 5.16.0 · fixed in 6.1.141; From 6.2.0 · fixed in 6.6.93; From 6.7.0 · fixed in 6.12.31; From 6.13.0 · fixed in 6.14.9

References 8