[PATCH 03/13] ide: Potential null pointer dereference in ide_queue_pc_tail()

The function blk_get_request() can return NULL in some cases. There are
checks on it if function is called with argumetns one of which is
GFP_ATOMIC/GFP_NOIO/etc. If system couldn't find request
blk_get_request() return NULL.

But if there is function call with argument __GFP_WAIT
the system will wait until get request or the queue becomes
dead. If something kills the queue, blk_get_request()
return NULL and next operations will lead to errors.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Marina Makienko <redacted>
---
 drivers/ide/ide-atapi.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/ide/ide-atapi.c b/drivers/ide/ide-atapi.c
index fac3d9d..8bf4109 100644
--- a/drivers/ide/ide-atapi.c
+++ b/drivers/ide/ide-atapi.c

@@ -93,6 +93,12 @@ int ide_queue_pc_tail(ide_drive_t *drive, struct gendisk *disk,
 	int error;
 
 	rq = blk_get_request(drive->queue, READ, __GFP_WAIT);
+
+	if (!rq) {
+		printk(KERN_ERR PFX"ide_queue_pc_tail: blk_get_request() failed. \n");
+		return 1;
+	}
+
 	rq->cmd_type = REQ_TYPE_SPECIAL;
 	rq->special = (char *)pc;
 

-- 
1.7.7