CVE-2025-38415

Technical 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

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References