libceph: do not dereference a NULL bio pointer

Commit f38a5181d9f3 ("ceph: Convert to immutable biovecs") introduced
a NULL pointer dereference, which broke rbd in -rc1.  Fix it.

Cc: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 0e478a0f4204..30efc5c18622 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -840,9 +840,13 @@ static bool ceph_msg_data_bio_advance(struct ceph_msg_data_cursor *cursor,
 
         if (!cursor->bvec_iter.bi_size) {
                 bio = bio->bi_next;
-                cursor->bvec_iter = bio->bi_iter;
+                cursor->bio = bio;
+                if (bio)
+                        cursor->bvec_iter = bio->bi_iter;
+                else
+                        memset(&cursor->bvec_iter, 0,
+                               sizeof(cursor->bvec_iter));
         }
-        cursor->bio = bio;
 
         if (!cursor->last_piece) {
                 BUG_ON(!cursor->resid);