From 0eb25bb027a100f5a9df8991f2f628e7d851bc1e Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Wed, 24 Jul 2013 15:37:42 +1000
Subject: md/raid10: remove use-after-free bug.

We always need to be careful when calling generic_make_request, as it
can start a chain of events which might free something that we are
using.

Here is one place I wasn't careful enough.  If the wbio2 is not in
use, then it might get freed at the first generic_make_request call.
So perform all necessary tests first.

This bug was introduced in 3.3-rc3 (24afd80d99) and can cause an
oops, so fix is suitable for any -stable since then.

Cc: stable@vger.kernel.org (3.3+)
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 957a719..df7b0a0 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2290,12 +2290,18 @@ static void recovery_request_write(struct mddev *mddev, struct r10bio *r10_bio)
 	d = r10_bio->devs[1].devnum;
 	wbio = r10_bio->devs[1].bio;
 	wbio2 = r10_bio->devs[1].repl_bio;
+	/* Need to test wbio2->bi_end_io before we call
+	 * generic_make_request as if the former is NULL,
+	 * the latter is free to free wbio2.
+	 */
+	if (wbio2 && !wbio2->bi_end_io)
+		wbio2 = NULL;
 	if (wbio->bi_end_io) {
 		atomic_inc(&conf->mirrors[d].rdev->nr_pending);
 		md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(wbio));
 		generic_make_request(wbio);
 	}
-	if (wbio2 && wbio2->bi_end_io) {
+	if (wbio2) {
 		atomic_inc(&conf->mirrors[d].replacement->nr_pending);
 		md_sync_acct(conf->mirrors[d].replacement->bdev,
 			     bio_sectors(wbio2));
-- 
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