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CVE-2026-97902 Affecting linux-6.12 package, versions <6.12.111-1~deb12u1

Severity

 Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.2% (9th percentile)

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  • Snyk IDSNYK-DEBIAN12-LINUX612-20507462
  • published5 Oct 2026
  • disclosed25 Sept 2026
Report a new vulnerability Found a mistake?

Introduced: 25 Sep 2026

NewCVE-2026-97902  (opens in a new tab)

How to fix?

Upgrade Debian:12 linux-6.12 to version 6.12.111-1~deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-6.12 package and not the linux-6.12 package as distributed by Debian. See How to fix? for Debian:12 relevant fixed versions and status.

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

fs: don't return -EINVAL for successful nested thaw

Commit 7366f8b6fc6a ("fs: handle freezing from multiple devices") replaced the freeze_holders bitmask with per-holder counters to allow nested freezes. In the bitmask version, a thaw that released a shared hold while another holder remained returned 0. Since the rework, thaw_super_locked() drops the freeze reference via freeze_dec() but then returns -EINVAL when other freezers remain, misinforming the caller: the thaw did succeed, the superblock just stays frozen for the remaining holders.

This breaks bdev-initiated freezing. When a filesystem is frozen with FIFREEZE and additionally frozen via bdev_freeze() -- which nests by design, see fs_bdev_freeze() -- the subsequent bdev_thaw() receives -EINVAL from the holder op although its freeze reference was dropped, and therefore keeps bd_fsfreeze_count elevated. Then device-mapper's unlock_fs() ignores bdev_thaw()'s return value, so nothing rebalances the count. After the user's FITHAW and umount, the block device can never be mounted again:

dm-1: Can&#39;t mount, blockdev is frozen

There is no way for userspace to drop the leaked count; only destroying the block device (or a reboot) recovers the device.

Reproducer (any kernel since v6.8):

dmsetup create dut --table &#34;0 $(blockdev --getsz &#34;$DEV&#34;) linear $DEV 0&#34;
mkfs.ext4 /dev/mapper/dut
mount /dev/mapper/dut /mnt
fsfreeze --freeze /mnt      # freeze_ucount == 1
dmsetup suspend dut         # bd_fsfreeze_count == 1, ucount == 2
dmsetup resume dut          # ucount 2 -&gt; 1, but thaw_super()
                            # returns -EINVAL, so bdev_thaw()
                            # keeps bd_fsfreeze_count at 1
fsfreeze --unfreeze /mnt    # filesystem thaws fine
umount /mnt
mount /dev/mapper/dut /mnt  # EBUSY, forever

The same happens with fsfreeze held across an LVM snapshot of the origin volume.

fs_bdev_thaw()'s documentation already describes the intended semantics: "If this function returns zero it doesn't mean that the filesystem is unfrozen as it may have been frozen multiple times". Restore them by returning 0 when a nested thaw drops its hold while other freezers remain. Thawing without holding a freeze still fails with -EINVAL as may_unfreeze() rejects that case before the reference count is touched.

CVSS Base Scores

version 3.1