Squashfs: check metadata block offset is within range

Syzkaller reports a "general protection fault in squashfs_copy_data"

This is ultimately caused by a corrupted index look-up table, which
produces a negative metadata block offset.

This is subsequently passed to squashfs_copy_data (via
squashfs_read_metadata) where the negative offset causes an out of bounds
access.

The fix is to check that the offset is within range in
squashfs_read_metadata.  This will trap this and other cases.

Link: https://lkml.kernel.org/r/20260217050955.138351-1-phillip@squashfs.org.uk
Fixes: f400e12656ab ("Squashfs: cache operations")
Reported-by: syzbot+a9747fe1c35a5b115d3f@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/699234e2.a70a0220.2c38d7.00e2.GAE@google.com/
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/squashfs/cache.c b/fs/squashfs/cache.c
index 8e958db5f78696dd68a4c0464d9c5ec7f1874c15..67abd4dff222235e75d8c2b10d5e9b811d6e38d8 100644 (file)
--- a/fs/squashfs/cache.c
+++ b/fs/squashfs/cache.c
@@ -344,6 +344,9 @@ int squashfs_read_metadata(struct super_block *sb, void *buffer,
        if (unlikely(length < 0))
                return -EIO;
 
+       if (unlikely(*offset < 0 || *offset >= SQUASHFS_METADATA_SIZE))
+               return -EIO;
+
        while (length) {
                entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
                if (entry->error) {