linux-kernel - [PATCH v2] block: fix possible NULL dereference

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Date:	Fri,  1 Apr 2016 15:34:18 +0100
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	Sudip Mukherjee <sudipm.mukherjee@...il.com>,
	Johannes Thumshirn <jthumshirn@...e.de>
Subject: [PATCH v2] block: fix possible NULL dereference

We were checking for iter to be NULL after dereferencing it. There is
actually no need to check for iter to be NULL as all the callers of
blk_rq_map_user_iov() does call it with a valid pointer to
struct iov_iter.
But as iter->count can be NULL so the assignment to copy is being done
after checking for it.

Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
---

v2: removed the check for iter
v1: moved the assignment to copy after check for iter and iter->count


 block/blk-map.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-map.c b/block/blk-map.c
index a54f054..e15b4aa 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -126,14 +126,15 @@ 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;
 
-	if (!iter || !iter->count)
+	if (!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;
 
-- 
2.1.4