CVE-2026-43118

What the bug is

When logging that an inode exists, as part of logging a new name or logging new dir entries for a directory, we always set the generation of the logged inode item to 0. This is to signal during log replay (in overwrite_item()), that we should not set the i_size since we only logged that an inode exists, so the i_size of the inode in the subvolume tree must be preserved (as when we log new names or that an inode exists, we don't log extents). This works fine except when we have already logged an inode in full mode or it's the first time we are logging an inode created in a past transaction, that inode has a new i_size of 0 and then we log a new name for the inode (due to a new hardlink or a rename), in which case we log an i_size of 0 for the inode and a generation of 0, which causes the log replay code to not update the inode's i_size to 0 (in overwrite_item()). An example scenario: mkdir /mnt/dir xfs_io -f -c "pwrite 0 64K" /mnt/dir/foo sync xfs_io -c "truncate 0" -c "fsync" /mnt/dir/foo ln /mnt/dir/foo /mnt/dir/bar xfs_io -c "fsync" /mnt/dir <power fail> After log replay the file remains with a size of 64K. This is because when we first log the inode, when we fsync file foo, we log its current i_size of 0, and then when we create a hard link we log again the inode in exists mode (LOG_INODE_EXISTS) but we set a generation of 0 for the inode item we add to the log tree, so during log replay overwrite_item() sees that the generation is 0 and i_size is 0 so we skip updating the inode's i_size from 64K to 0. Fix this by making sure at fill_inode_item() we always log the real generation of the inode if it was logged in the current transaction with the i_size we logged before. Also if an inode created in a previous transaction is logged in exists mode only, make sure we log the i_size stored in the inode item located from the commit root, so that if we log multiple times that the inode exists we get the correct i_size. A test case for fstests will follow soon.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

fs/btrfs/tree-log.c

What this is

BTRFS FILE SYSTEMMAINTAINERS section matched on fs/btrfs/ · linux-btrfs@vger.kernel.org · Maintained

Kernel module

btrfs

Check it on the machine

grep -w CONFIG_BTRFS_FS /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

lsmod | grep -w btrfs

Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.

Show whether Debian builds this, per release

Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.

• bookworm, trixie, forky, sidm

m

a loadable module on every flavour - check lsmod, can be blacklisted

Build switch

CONFIG_BTRFS_FS

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-05-06 (5 months ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.16%, higher than 4.8% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

fs/btrfs

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
2.6.30	6.18.24	fddb157536e6
2.6.30	6.19.14	03e966b63df5
2.6.30	7.0	5254d4181add