linux-kernel - [PATCH 3.18 36/49] ext4: fix potential use after free in __ext4_journal

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Date:   Thu, 18 May 2017 15:16:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lukas Czerner <lczerner@...hat.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Amit Pundir <amit.pundir@...aro.org>
Subject: [PATCH 3.18 36/49] ext4: fix potential use after free in __ext4_journal_stop

3.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Lukas Czerner <lczerner@...hat.com>

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@...hat.com>
Reviewed-by: Andreas Dilger <adilger@...ger.ca>
Signed-off-by: Amit Pundir <amit.pundir@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/ext4_jbd2.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -88,13 +88,13 @@ int __ext4_journal_stop(const char *wher
 		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)