Overview
About vulnerability
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.
Details
- Affected product:
- AlmaLinux 9.2 ESU , CentOS 6 ELS , CentOS 7 ELS , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , CloudLinux 7 ELS , Oracle Linux 6 ELS , Oracle Linux 7 ELS , RHEL 7 ELS , TuxCare 9.6 ESU , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS , Ubuntu 20.04 ELS
- Affected packages:
- kernel @ 3.10.0 (+15 more)
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.