rbd: expand rbd_dev_ondisk_valid() checks

Add checks on the validity of the snap_count and snap_names_len
field values in rbd_dev_ondisk_valid().  This eliminates the
need to do them in rbd_header_from_disk().

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 27 insertions, 9 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index aff4e8a01ea5..5bcd4ebb22e7 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -481,8 +481,31 @@ static void rbd_coll_release(struct kref *kref)
 
 static bool rbd_dev_ondisk_valid(struct rbd_image_header_ondisk *ondisk)
 {
-        return !memcmp(&ondisk->text,
-                        RBD_HEADER_TEXT, sizeof (RBD_HEADER_TEXT));
+        size_t size;
+        u32 snap_count;
+
+        /* The header has to start with the magic rbd header text */
+        if (memcmp(&ondisk->text, RBD_HEADER_TEXT, sizeof (RBD_HEADER_TEXT)))
+                return false;
+
+        /*
+         * The size of a snapshot header has to fit in a size_t, and
+         * that limits the number of snapshots.
+         */
+        snap_count = le32_to_cpu(ondisk->snap_count);
+        size = SIZE_MAX - sizeof (struct ceph_snap_context);
+        if (snap_count > size / sizeof (__le64))
+                return false;
+
+        /*
+         * Not only that, but the size of the entire the snapshot
+         * header must also be representable in a size_t.
+         */
+        size -= snap_count * sizeof (__le64);
+        if ((u64) size < le64_to_cpu(ondisk->snap_names_len))
+                return false;
+
+        return true;
 }
 
 /*
@@ -499,15 +522,10 @@ static int rbd_header_from_disk(struct rbd_image_header *header,
         if (!rbd_dev_ondisk_valid(ondisk))
                 return -ENXIO;
 
-        snap_count = le32_to_cpu(ondisk->snap_count);
-
-        /* Make sure we don't overflow below */
-        size = SIZE_MAX - sizeof (struct ceph_snap_context);
-        if (snap_count > size / sizeof (header->snapc->snaps[0]))
-                return -EINVAL;
-
         memset(header, 0, sizeof (*header));
 
+        snap_count = le32_to_cpu(ondisk->snap_count);
+
         size = sizeof (ondisk->block_name) + 1;
         header->object_prefix = kmalloc(size, GFP_KERNEL);
         if (!header->object_prefix)