CVE-2026-23238: Linux Kernel

Medium severity, CVSS 5.5. EPSS: 0.2% chance of exploitation in the next 30 days.

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 Linux Kernel: from 2.6.12.1, before 5.10.251 (fixed in 5.10.251); from 5.11, before 5.15.201 (fixed in 5.15.201); from 5.16, before 6.1.164 (fixed in 6.1.164); from 6.2, before 6.6.127 (fixed in 6.6.127); from 6.7, before 6.12.74 (fixed in 6.12.74); from 6.13, before 6.18.13 (fixed in 6.18.13); …

Published 2026-03-04. Last modified 2026-06-17.