CVE-2026-43361 — btrfs: fix transaction abort when snapshotting received subvolumes

Affected: Linux

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

btrfs: fix transaction abort when snapshotting received subvolumes

Currently a user can trigger a transaction abort by snapshotting a previously received snapshot a bunch of times until we reach a BTRFS_UUID_KEY_RECEIVED_SUBVOL item overflow (the maximum item size we can store in a leaf). This is very likely not common in practice, but if it happens, it turns the filesystem into RO mode. The snapshot, send and set_received_subvol and subvol_setflags (used by receive) don't require CAP_SYS_ADMIN, just inode_owner_or_capable(). A malicious user could use this to turn a filesystem into RO mode and disrupt a system.

Reproducer script:

$ cat test.sh #!/bin/bash

DEV=/dev/sdi MNT=/mnt/sdi

# Use smallest node size to make the test faster. mkfs.btrfs -f --nodesize 4K $DEV mount $DEV $MNT

# Create a subvolume and set it to RO so that it can be used for send. btrfs subvolume create $MNT/sv touch $MNT/sv/foo btrfs property set $MNT/sv ro true

# Send and receive the subvolume into snaps/sv. mkdir $MNT/snaps btrfs send $MNT/sv | btrfs receive $MNT/snaps

# Now snapshot the received subvolume, which has a received_uuid, a # lot of times to trigger the leaf overflow. total=500 for ((i = 1; i <= $total; i++)); do echo -ne "\rCreating snapshot $i/$total" btrfs subvolume snapshot -r $MNT/snaps/sv $MNT/snaps/sv_$i > /dev/null done echo

umount $MNT

When running the…

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CVE-2026-43361 — btrfs: fix transaction abort when snapshotting received subvolumes

USN-8567-1 — linux, linux-gcp, linux-gcp-6.8, linux-gke, linux-gkeop, linux-realtime, linux-realtime-6.8 vulnerabilities