CVE-2026-23238 romfs: check sb_set_blocksize() return value
A local attacker can cause a kernel crash by mounting a romfs filesystem on a loop device with an incompatible block size, leading to denial of service.
- 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-2026-23238?
CVE-2026-23238 is a medium-severity vulnerability in Linux kernel, published on 4 Mar 2026. 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:
romfs: check sb_set_blocksize() return value
romfs_fill_super() ignores the return value of sb_set_blocksize(), which can fail if the requested block size is incompatible with the block device's configuration.
This can be triggered by setting a loop device's block size larger than PAGE_SIZE using ioctl(LOOP_SET_BLOCK_SIZE, 32768), then mounting a romfs filesystem on that device.
When sb_set_blocksize(sb, ROMBSIZE) is called with ROMBSIZE=4096 but the device has logical_block_size=32768, bdev_validate_blocksize() fails because the requested size is smaller than the device's logical block size. sb_set_blocksize() returns 0 (failure), but romfs ignores this and continues mounting.
The superblock's block size remains at the device's logical block size (32768). Later, when sb_bread() attempts I/O with this oversized block size, it triggers a kernel BUG in folio_set_bh():
kernel BUG at fs/buffer.c:1582! BUG_ON(size > PAGE_SIZE);
Fix by checking the return value of sb_set_blocksize() and failing the mount with -EINVAL if it returns 0.
Weakness: CWE-617
Which versions are affected by CVE-2026-23238?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23238?
Apply the vendor's patch.
Is CVE-2026-23238 being exploited?
There is no known exploitation of CVE-2026-23238 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-23238, DEBIAN-CVE-2026-23238, GHSA-wj4m-w3qm-xpch, ROOT-OS-DEBIAN-11-CVE-2026-23238, ROOT-OS-DEBIAN-12-CVE-2026-23238, ROOT-OS-DEBIAN-13-CVE-2026-23238 and 3 more.