From 69e0927b3774563c19b5fb32e91d75edc147fb62 Mon Sep 17 00:00:00 2001
From: Douglas Gilbert <dgilbert@interlog.com>
Date: Sun, 14 Jan 2018 17:00:48 -0500
Subject: blk_rq_map_user_iov: fix error override

From: Douglas Gilbert <dgilbert@interlog.com>

commit 69e0927b3774563c19b5fb32e91d75edc147fb62 upstream.

During stress tests by syzkaller on the sg driver the block layer
infrequently returns EINVAL. Closer inspection shows the block
layer was trying to return ENOMEM (which is much more
understandable) but for some reason overroad that useful error.

Patch below does not show this (unchanged) line:
   ret =__blk_rq_map_user_iov(rq, map_data, &i, gfp_mask, copy);
That 'ret' was being overridden when that function failed.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 block/blk-map.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -116,7 +116,7 @@ int blk_rq_map_user_iov(struct request_q
 	unsigned long align = q->dma_pad_mask | queue_dma_alignment(q);
 	struct bio *bio = NULL;
 	struct iov_iter i;
-	int ret;
+	int ret = -EINVAL;
 
 	if (!iter_is_iovec(iter))
 		goto fail;
@@ -145,7 +145,7 @@ unmap_rq:
 	__blk_rq_unmap_user(bio);
 fail:
 	rq->bio = NULL;
-	return -EINVAL;
+	return ret;
 }
 EXPORT_SYMBOL(blk_rq_map_user_iov);