From: Phillip Lougher <phillip@squashfs.org.uk> stable inclusion from stable-v5.10.238 commit 549f9e3d7b60d53808c98b9fde49b4f46d0524a5 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/ICOXJK CVE: CVE-2025-38415 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=t... -------------------------------- [ Upstream commit 734aa85390ea693bb7eaf2240623d41b03705c84 ] 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(). Link: https://lkml.kernel.org/r/20250409024747.876480-1-phillip@squashfs.org.uk Fixes: 0aa666190509 ("Squashfs: super block operations") Reported-by: syzbot+65761fc25a137b9c8c6e@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67f0dd7a.050a0220.0a13.0230.GAE@google.com/ Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Long Li <leo.lilong@huawei.com> --- fs/squashfs/super.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c index f7128ae7b949..bb2958ad8a6f 100644 --- a/fs/squashfs/super.c +++ b/fs/squashfs/super.c @@ -118,6 +118,11 @@ static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc) msblk = sb->s_fs_info; msblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE); + if (!msblk->devblksize) { + errorf(fc, "squashfs: unable to set blocksize\n"); + return -EINVAL; + } + msblk->devblksize_log2 = ffz(~msblk->devblksize); mutex_init(&msblk->meta_index_mutex); -- 2.39.2