CVE-2022-49769 gfs2: Check sb_bsize_shift after reading superblock
A missing validation of the block size shift field in the GFS2 filesystem allows attackers to cause a kernel crash or mount failure via crafted superblocks.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2022-49769?
CVE-2022-49769 is a medium-severity vulnerability in Linux kernel, published on 1 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
gfs2: Check sb_bsize_shift after reading superblock
Fuzzers like to scribble over sb_bsize_shift but in reality it's very unlikely that this field would be corrupted on its own. Nevertheless it should be checked to avoid the possibility of messy mount errors due to bad calculations. It's always a fixed value based on the block size so we can just check that it's the expected value.
Tested with:
mkfs.gfs2 -O -p lock_nolock /dev/vdb for i in 0 -1 64 65 32 33; do gfs2_edit -p sb field sb_bsize_shift $i /dev/vdb mount /dev/vdb /mnt/test && umount /mnt/test done
Before this patch we get a withdraw after
[ 76.413681] gfs2: fsid=loop0.0: fatal: invalid metadata block [ 76.413681] bh = 19 (type: exp=5, found=4) [ 76.413681] function = gfs2_meta_buffer, file = fs/gfs2/meta_io.c, line = 492
and with UBSAN configured we also get complaints like
[ 76.373395] UBSAN: shift-out-of-bounds in fs/gfs2/ops_fstype.c:295:19 [ 76.373815] shift exponent 4294967287 is too large for 64-bit type 'long unsigned int'
After the patch, these complaints don't appear, mount fails immediately and we get an explanation in dmesg.
Which versions are affected by CVE-2022-49769?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-49769?
Apply the vendor's patch.
Is CVE-2022-49769 being exploited?
There is no known exploitation of CVE-2022-49769 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2022-49769, GHSA-22ff-fvm7-6wj7, UBUNTU-CVE-2022-49769.