squashfs: fix inode lookup sanity checks

When mouting a squashfs image created without inode compression it fails
with: "unable to read inode lookup table"

It turns out that the BLOCK_OFFSET is missing when checking the
SQUASHFS_METADATA_SIZE agaist the actual size.

Link: https://lkml.kernel.org/r/20210226092903.1473545-1-sean@geanix.com
Fixes: eabac19e ("squashfs: add more sanity checks in inode lookup")
Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Acked-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/squashfs/export.c

@@ -152,14 +152,18 @@ __le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
 		start = le64_to_cpu(table[n]);
 		end = le64_to_cpu(table[n + 1]);
 
-		if (start >= end || (end - start) > SQUASHFS_METADATA_SIZE) {
+		if (start >= end
+		    || (end - start) >
+		    (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
 			kfree(table);
 			return ERR_PTR(-EINVAL);
 		}
 	}
 
 	start = le64_to_cpu(table[indexes - 1]);
-	if (start >= lookup_table_start || (lookup_table_start - start) > SQUASHFS_METADATA_SIZE) {
+	if (start >= lookup_table_start ||
+	    (lookup_table_start - start) >
+	    (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
 		kfree(table);
 		return ERR_PTR(-EINVAL);
 	}

fs/squashfs/squashfs_fs.h

@@ -17,6 +17,7 @@
 
 /* size of metadata (inode and directory) blocks */
 #define SQUASHFS_METADATA_SIZE		8192
+#define SQUASHFS_BLOCK_OFFSET		2
 
 /* default size of block device I/O */
 #ifdef CONFIG_SQUASHFS_4K_DEVBLK_SIZE