[PATCH] Squashfs: check metadata block offset is within range

[Phillip Lougher]

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.

Fixes: f400e12656ab ("Squashfs: cache operations")
Reported-by: syzbot+a9747fe1c35a5b115d3f@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/699234e2.a70a0220.2c38d7.00e2.GAE@xxxxxxxxxx/

Signed-off-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
---
 fs/squashfs/cache.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/squashfs/cache.c b/fs/squashfs/cache.c
index 181260e72680..92fb857d2c76 100644
--- 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) {
-- 
2.47.3