CVE-2026-23238: romfs: check sb_set_blocksize() return value

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-04 · updated 2026-06-17
Weakness: CWE-617

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.

Affected products

Linux kernel: from 2.6.12.1 before 5.10.251; from 5.11 before 5.15.201; from 5.16 before 6.1.164; from 6.2 before 6.6.127; from 6.7 before 6.12.74; from 6.13 before 6.18.13 — fixed in 5.10.251, 5.15.201, 6.1.164, 6.12.74, 6.18.13, 6.6.127

How to fix

Upgrade to a fixed version: Linux kernel 5.10.251, 5.15.201, 6.1.164, 6.12.74. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-23238 or the next vulnerability affects your stack