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[PATCH 3.16.y-ckt 029/126] ext4: fix potential use after free in __ext4_journal_stop

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  [PATCH 3.16.y-ckt 029/126] ext4: fix potential use after free in __ext4_journal_stop Luis Henriques <luis.henriques@canonical.com> - 2015-12-09 11:40 +0100

#1287380 — [PATCH 3.16.y-ckt 029/126] ext4: fix potential use after free in __ext4_journal_stop

3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.

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

From: Lukas Czerner <lczerner@redhat.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@redhat.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Luis Henriques <luis.henriques@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)
--
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