Squashfs: add sanity checks to fragment reading at mount time

Fsfuzzer generates corrupted filesystems which throw a warn_on in
kmalloc.  One of these is due to a corrupted superblock fragments field.
Fix this by checking that the number of bytes to be read (and allocated)
does not extend into the next filesystem structure.

Also add a couple of other sanity checks of the mount-time fragment table
structures.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index 80a7119870a6..efa8118260d4 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -261,6 +261,7 @@ allocate_id_index_table:
 		msblk->inode_lookup_table = NULL;
 		goto failed_mount;
 	}
+	next_table = msblk->inode_lookup_table[0];
 
 	sb->s_export_op = &squashfs_export_ops;
 
@@ -278,7 +279,7 @@ handle_fragments:
 
 	/* Allocate and read fragment index table */
 	msblk->fragment_index = squashfs_read_fragment_index_table(sb,
-		le64_to_cpu(sblk->fragment_table_start), fragments);
+		le64_to_cpu(sblk->fragment_table_start), next_table, fragments);
 	if (IS_ERR(msblk->fragment_index)) {
 		ERROR("unable to read fragment index table\n");
 		err = PTR_ERR(msblk->fragment_index);