[3.16.y-ckt stable] Patch "ext4: fix potential use after free in __ext4_journal_stop" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ext4: fix potential use after free in __ext4_journal_stop

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt21.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 310c4cd2fef847742ea63111e341b23a71d80c40 Mon Sep 17 00:00:00 2001
From: Lukas Czerner <lczerner at redhat.com>
Date: Sat, 17 Oct 2015 22:57:06 -0400
Subject: ext4: fix potential use after free in __ext4_journal_stop

commit 6934da9238da947628be83635e365df41064b09b upstream.

There is a use-after-free possibility in __ext4_journal_stop() in the
case that we free the handle in the first jbd2_journal_stop() because
we're referencing handle->h_err afterwards. This was introduced in
9705acd63b125dee8b15c705216d7186daea4625 and it is wrong. Fix it by
storing the handle->h_err value beforehand and avoid referencing
potentially freed handle.

Fixes: 9705acd63b125dee8b15c705216d7186daea4625
Signed-off-by: Lukas Czerner <lczerner at redhat.com>
Reviewed-by: Andreas Dilger <adilger at dilger.ca>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/ext4/ext4_jbd2.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 44c89188c62c..23349f00e77c 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -88,13 +88,13 @@ int __ext4_journal_stop(const char *where, unsigned int line, handle_t *handle)
 		return 0;
 	}

+	err = handle->h_err;
 	if (!handle->h_transaction) {
-		err = jbd2_journal_stop(handle);
-		return handle->h_err ? handle->h_err : err;
+		rc = jbd2_journal_stop(handle);
+		return err ? err : rc;
 	}

 	sb = handle->h_transaction->t_journal->j_private;
-	err = handle->h_err;
 	rc = jbd2_journal_stop(handle);

 	if (!err)