Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Stephen Brennan <stephen.s.brennan@oracle.com>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Jens Axboe <axboe@kernel.dk>,
        Dmitry Kadashev <dkadashev@gmail.com>
Cc:     Stephen Brennan <stephen.s.brennan@oracle.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v3 1/4] namei: Fix use after free in kern_path_locked
Date:   Tue,  7 Sep 2021 17:04:10 -0700
Message-Id: <20210908000413.42264-2-stephen.s.brennan@oracle.com>
In-Reply-To: <20210908000413.42264-1-stephen.s.brennan@oracle.com>
References: <20210908000413.42264-1-stephen.s.brennan@oracle.com>
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?XonR0pnmO98HA2yIdG0AbI0WoXim6MeP9PSXB4x5cCV0xTp7EkQ+0To4HfOn?=
 =?us-ascii?Q?mBDrQK37caxJ6icKe0wJEpHAnOGyfPnIjh/nxk2hstsFEthFI655ZB8CH+Ja?=
 =?us-ascii?Q?GJKERrvUmmRHp+0aeZFo9YsGTRYZXRalZbCzAJwfpdti7p61AhKCgRRUe0Ic?=
 =?us-ascii?Q?t18drc+0b89ZWdDte+7WP5hMxacnbGjgmxA5+FA3YVGHUZ969lODhIV+jMPE?=
 =?us-ascii?Q?Lt2oJ6bxOF2VXe34KxpSaaIRwtxwe8rwKbk4Ds7F7K709q98k4JI28w7hfqn?=
 =?us-ascii?Q?vjU7Qmdms9yq3TBGbgQD5s6hEK8BxImf+1N9wz0F/FyxPvRioS+Eo9c6dv2A?=
 =?us-ascii?Q?qb+v8PsSstjQfMq5wsr6FxwIhaeCs3cjIXyhpJ/JALLbsyVAmvQTYD5uxhL7?=
 =?us-ascii?Q?tSNztj+Y6Yj7WyCa0MLP+LrsTU8DBNg1CibYgxbl/V4iE4MCPHJewgX542e0?=
 =?us-ascii?Q?tHBtX+N9CwGUrqhvYHpaxW3IiiBhDpEl71RusnbYiA0TLEApO3r2sKUjm3uk?=
 =?us-ascii?Q?bCqWkXEa6DRoxIbqDl4wOg9zKkASSusSFqJ8NQFIyoRKnEZZekCk8s9z73HG?=
 =?us-ascii?Q?skVXo6HTF3g1zq5kFGaXW8x+yZma6/nn9mUjKqrtbLt5Qm8djtr9bvJPI5ud?=
 =?us-ascii?Q?LIcTaw3mo+IBDCk7ta4twmuEZGNrIFq3YnIKKDOOLaFuZzI9g+blX/7TakBi?=
 =?us-ascii?Q?h6Yy8x1Ict0baCojdexirGZpc9e+zo/Vzud0QloQ19F+6/pPJHKKmA+xoFdJ?=
 =?us-ascii?Q?+G6LGpyO3zCBT8FKRLBVfePo1wd5Y7jUjopwUW/wGsNwwVu5u28Fk9sFDSkh?=
 =?us-ascii?Q?C0ImZ1c9WipNxQ80yRXipBbe1XqRRx7Z6p3eINLDqtswGKTQNNr/eERdhE74?=
 =?us-ascii?Q?1sIbbKnaAV7BqtE/g86PYF9qA/iPmmKvNJ3b+2/24KPrnbcy4nmHiGTACJkP?=
 =?us-ascii?Q?l0+mJ6MLNwyI3ludUyccCRhZW1uceif8dRqxihyMoh/pW2TUUq6ASsBuPHKf?=
 =?us-ascii?Q?4W2Q6Eo6GqfZDYeWW0RS+i0T6RgbzcZYZuY+N80Fl6LorNZ3BasvAXPBpA6c?=
 =?us-ascii?Q?5bDhhEl4vvDRVjgatfx6Bz7biEuBxhcXbYFFKt/tKG7h3Q5PT6pIj1EWeJce?=
 =?us-ascii?Q?fLFg0oLPneAD9HV+V8P5FvS/SJUn3vcF+fjh7RrRolTsVBIBW1r6GGk1+kCV?=
 =?us-ascii?Q?j/edxgs7JKLf5pzF7Qj/Gq+zMm5aOlKweomrUnAiAQoIy7RCYqcIkdahqdtO?=
 =?us-ascii?Q?jm3iBj0S7N68dO/0W3hKQslFYgQERY1d/0se/BQcPSMe0i5xolya0/5ba32u?=
 =?us-ascii?Q?GrLHjweCrMvJM+CiVKN3DoS3?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 20e113d2-a03d-4e5c-2db6-08d9725c314b
X-MS-Exchange-CrossTenant-AuthSource: CH2PR10MB4166.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Sep 2021 00:04:14.0563
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: uOoMYkJCCeJ5Ej04VCaQPfnAg6qEbYHOEjgXnyoxx0WvQZBlfDd1259umZfY6pj1nbx+xhTOvSRmUr1hthKmDtlYGQ0Lm8DAIMiQVwx5+Ag=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR10MB5147
X-Proofpoint-Virus-Version: vendor=nai engine=6300 definitions=10100 signatures=668682
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 bulkscore=0 malwarescore=0
 mlxscore=0 adultscore=0 phishscore=0 mlxlogscore=999 suspectscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109030001
 definitions=main-2109070152
X-Proofpoint-GUID: OE6hsEy7A-tx8C6hGXUS0ud739v0Zk5k
X-Proofpoint-ORIG-GUID: OE6hsEy7A-tx8C6hGXUS0ud739v0Zk5k
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

In 0ee50b47532a ("namei: change filename_parentat() calling
conventions"), filename_parentat() was made to always call putname() on
the  filename before returning, and kern_path_locked() was migrated to
this calling convention. However, kern_path_locked() uses the "last"
parameter to lookup and potentially create a new dentry. The last
parameter contains the last component of the path and points within the
filename, which was recently freed at the end of filename_parentat().
Thus, when kern_path_locked() calls __lookup_hash(), it is using the
filename after it has already been freed.

Switch to using __filename_parentat() to avoid freeing the filename, and
wrap the function with a getname and putname instead. Remove
filename_parentat() as it is now unused, and it is inherently broken.

Fixes: 0ee50b47532a ("namei: change filename_parentat() calling conventions")
Link: https://lore.kernel.org/linux-fsdevel/YTfVE7IbbTV71Own@zeniv-ca.linux.org.uk/
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: syzbot+fb0d60a179096e8c2731@syzkaller.appspotmail.com
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
---
 fs/namei.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index d049d3972695..d6340fabaab4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2538,25 +2538,15 @@ static int __filename_parentat(int dfd, struct filename *name,
 	return retval;
 }
 
-static int filename_parentat(int dfd, struct filename *name,
-				unsigned int flags, struct path *parent,
-				struct qstr *last, int *type)
-{
-	int retval = __filename_parentat(dfd, name, flags, parent, last, type);
-
-	putname(name);
-	return retval;
-}
-
 /* does lookup, returns the object with parent locked */
-struct dentry *kern_path_locked(const char *name, struct path *path)
+static struct dentry *__kern_path_locked(struct filename *name,
+					 struct path *path)
 {
 	struct dentry *d;
 	struct qstr last;
 	int type, error;
 
-	error = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,
-				    &last, &type);
+	error = __filename_parentat(AT_FDCWD, name, 0, path, &last, &type);
 	if (error)
 		return ERR_PTR(error);
 	if (unlikely(type != LAST_NORM)) {
@@ -2572,6 +2562,15 @@ struct dentry *kern_path_locked(const char *name, struct path *path)
 	return d;
 }
 
+struct dentry *kern_path_locked(const char *name, struct path *path)
+{
+	struct filename *filename = getname_kernel(name);
+	struct dentry *res = __kern_path_locked(filename, path);
+
+	putname(filename);
+	return res;
+}
+
 int kern_path(const char *name, unsigned int flags, struct path *path)
 {
 	return filename_lookup(AT_FDCWD, getname_kernel(name),
-- 
2.30.2