md/raid10: remove use-after-free bug.

commit 0eb25bb027a100f5a9df8991f2f628e7d851bc1e upstream.

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.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index d61eb7ea0d81..081bb3345353 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2268,12 +2268,18 @@ 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));