CVE-2025-38415Squashfs: check return result of sb_min_blocksize

Official description

In the Linux kernel, the following vulnerability has been resolved: Squashfs: check return result of sb_min_blocksize Syzkaller reports an "UBSAN: shift-out-of-bounds in squashfs_bio_read" bug. Syzkaller forks multiple processes which after mounting the Squashfs filesystem, issues an ioctl("/dev/loop0", LOOP_SET_BLOCK_SIZE, 0x8000). Now if this ioctl occurs at the same time another process is in the process of mounting a Squashfs filesystem on /dev/loop0, the failure occurs. When this happens the following code in squashfs_fill_super() fails. ---- msblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE); msblk->devblksize_log2 = ffz(~msblk->devblksize); ---- sb_min_blocksize() returns 0, which means msblk->devblksize is set to 0. As a result, ffz(~msblk->devblksize) returns 64, and msblk->devblksize_log2 is set to 64. This subsequently causes the UBSAN: shift-out-of-bounds in fs/squashfs/block.c:195:36 shift exponent 64 is too large for 64-bit type 'u64' (aka 'unsigned long long') This commit adds a check for a 0 return by sb_min_blocksize().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/db7096ea160e40d78c67fce52e7cc51bde049497
• https://git.kernel.org/stable/c/549f9e3d7b60d53808c98b9fde49b4f46d0524a5
• https://git.kernel.org/stable/c/5c51aa862cbeed2f3887f0382a2708956710bd68
• https://git.kernel.org/stable/c/6abf6b78c6fb112eee495f5636ffcc350dd2ce25
• https://git.kernel.org/stable/c/4f99357dadbf9c979ad737156ad4c37fadf7c56b
• https://git.kernel.org/stable/c/0aff95d9bc7fb5400ca8af507429c4b067bdb425
• https://git.kernel.org/stable/c/295ab18c2dbce8d0ac6ecf7c5187e16e1ac8b282
• https://git.kernel.org/stable/c/734aa85390ea693bb7eaf2240623d41b03705c84
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html