linux-kernel - [PATCH] direct-io: Prevent NULL pointer access in submit_page

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Message-Id: <20171009091318.26714-1-agruenba@redhat.com>
Date:   Mon,  9 Oct 2017 11:13:18 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>, Jan Kara <jack@...e.cz>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        cluster-devel@...hat.com
Subject: [PATCH] direct-io: Prevent NULL pointer access in submit_page_section

In the code added to function submit_page_section by commit b1058b981,
sdio->bio can currently be NULL when calling dio_bio_submit.  This then
leads to a NULL pointer access in dio_bio_submit, so check for a NULL
bio in submit_page_section before trying to submit it instead.

Fixes xfstest generic/250 on gfs2.

Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 fs/direct-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 5fa2211e49ae..e0332da392d8 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -838,7 +838,8 @@ submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
 	 */
 	if (sdio->boundary) {
 		ret = dio_send_cur_page(dio, sdio, map_bh);
-		dio_bio_submit(dio, sdio);
+		if (sdio->bio)
+			dio_bio_submit(dio, sdio);
 		put_page(sdio->cur_page);
 		sdio->cur_page = NULL;
 	}
-- 
2.13.5