linux-kernel - [PATCH] block: fix possible NULL dereference

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Date:	Thu, 10 Mar 2016 17:09:13 +0530
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Jens Axboe <axboe@...nel.dk>, Jens Axboe <axboe@...com>
Cc:	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: [PATCH] block: fix possible NULL dereference

We were checking for iter to be NULL after dereferencing it. Lets first
check it and then use it.

Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
---
 block/blk-map.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index a54f054..089ed59 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -126,7 +126,7 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 			const struct iov_iter *iter, gfp_t gfp_mask)
 {
 	struct iovec iov, prv = {.iov_base = NULL, .iov_len = 0};
-	bool copy = (q->dma_pad_mask & iter->count) || map_data;
+	bool copy;
 	struct bio *bio = NULL;
 	struct iov_iter i;
 	int ret;
@@ -134,6 +134,7 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	if (!iter || !iter->count)
 		return -EINVAL;
 
+	copy = (q->dma_pad_mask & iter->count) || map_data;
 	iov_for_each(iov, i, *iter) {
 		unsigned long uaddr = (unsigned long) iov.iov_base;
 
-- 
1.9.1