Squashfs: add sanity checks to id reading at mount time

Fsfuzzer generates corrupted filesystems which throw a warn_on in
kmalloc.  One of these is due to a corrupted superblock no_ids 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 id table
structures.

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

1 files changed, 28 insertions, 2 deletions

diff --git a/fs/squashfs/id.c b/fs/squashfs/id.c
index 2fdac6703b48..499d08a1f34a 100644
--- a/fs/squashfs/id.c
+++ b/fs/squashfs/id.c
@@ -66,11 +66,37 @@ int squashfs_get_id(struct super_block *sb, unsigned int index,
  * Read uncompressed id lookup table indexes from disk into memory
  */
 __le64 *squashfs_read_id_index_table(struct super_block *sb,
-                        u64 id_table_start, unsigned short no_ids)
+                u64 id_table_start, u64 next_table, unsigned short no_ids)
 {
         unsigned int length = SQUASHFS_ID_BLOCK_BYTES(no_ids);
+        __le64 *table;
 
         TRACE("In read_id_index_table, length %d\n", length);
 
-        return squashfs_read_table(sb, id_table_start, length);
+        /* Sanity check values */
+
+        /* there should always be at least one id */
+        if (no_ids == 0)
+                return ERR_PTR(-EINVAL);
+
+        /*
+         * length bytes should not extend into the next table - this check
+         * also traps instances where id_table_start is incorrectly larger
+         * than the next table start
+         */
+        if (id_table_start + length > next_table)
+                return ERR_PTR(-EINVAL);
+
+        table = squashfs_read_table(sb, id_table_start, length);
+
+        /*
+         * table[0] points to the first id lookup table metadata block, this
+         * should be less than id_table_start
+         */
+        if (!IS_ERR(table) && table[0] >= id_table_start) {
+                kfree(table);
+                return ERR_PTR(-EINVAL);
+        }
+
+        return table;
 }