[Qemu-block] [PATCH] block: check BlockDriverState object before dereference

[P J P]

From: Prasad J Pandit <p...@fedoraproject.org>

When processing ATA_CACHE_FLUSH ide controller command,
BlockDriverState object could be null. Add check to avoid
null pointer dereference.

Reported-by: Kieron Shorrock <kshorr...@paloaltonetworks.com>
Signed-off-by: Prasad J Pandit <p...@fedoraproject.org>
---
 block/block-backend.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 0df3457..6a543a4 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1168,8 +1168,13 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, 
int64_t offset, int bytes,
 {
     BlkAioEmAIOCB *acb;
     Coroutine *co;
+    BlockDriverState *bs = blk_bs(blk);
 
-    bdrv_inc_in_flight(blk_bs(blk));
+    if (!bs) {
+        return NULL;
+    }
+
+    bdrv_inc_in_flight(bs);
     acb = blk_aio_get(&blk_aio_em_aiocb_info, blk, cb, opaque);
     acb->rwco = (BlkRwCo) {
         .blk    = blk,
@@ -1182,7 +1187,7 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, 
int64_t offset, int bytes,
     acb->has_returned = false;
 
     co = qemu_coroutine_create(co_entry, acb);
-    bdrv_coroutine_enter(blk_bs(blk), co);
+    bdrv_coroutine_enter(bs, co);
 
     acb->has_returned = true;
     if (acb->rwco.ret != NOT_DONE) {
-- 
2.9.4