linux-kernel - [PATCH 3.16 099/204] direct-io: Prevent NULL pointer access in submit_page

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Message-ID: <lsq.1514480744.263907769@decadent.org.uk>
Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Al Viro" <viro@...iv.linux.org.uk>,
        "Andreas Gruenbacher" <agruenba@...hat.com>,
        "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.16 099/204] direct-io: Prevent NULL pointer access in
 submit_page_section

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andreas Gruenbacher <agruenba@...hat.com>

commit 899f0429c7d3eed886406cd72182bee3b96aa1f9 upstream.

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>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/direct-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -812,7 +812,8 @@ out:
 	 */
 	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);
 		page_cache_release(sdio->cur_page);
 		sdio->cur_page = NULL;
 	}