Linux Kernel romfs: Ignoring sb_set_blocksize() causes BLOCKSIZE BUG
CVE-2026-23238 Published on March 4, 2026
romfs: check sb_set_blocksize() return value
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.
Products Associated with CVE-2026-23238
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below a381f0f61b35c8894b0bd0d6acef2d8f9b08b244 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below f2521ab1f63a8c244f06a080319e5ff9a2e1bd95 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 2c5829cd8fbbc91568c520b666898f57cdcb8cf6 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below cbd9931e6456822067725354d83446c5bb813030 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 9b203b8ddd7359270e8a694d0584743555128e2c is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 4b71ad7676564a94ec5f7d18298f51e8ae53db73 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below ab7ad7abb3660c58ffffdf07ff3bb976e7e0afa0 is affected.
- Version 5.10.251, <= 5.10.* is unaffected.
- Version 5.15.201, <= 5.15.* is unaffected.
- Version 6.1.164, <= 6.1.* is unaffected.
- Version 6.6.127, <= 6.6.* is unaffected.
- Version 6.12.74, <= 6.12.* is unaffected.
- Version 6.18.13, <= 6.18.* is unaffected.
- Version 6.19, <= * is unaffected.