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[2/7] FS-Cache: fix dereference of NULL user_key_payload

Message ID 20170928212602.41744-3-ebiggers3@gmail.com (mailing list archive)
State Not Applicable
Headers show

Commit Message

Eric Biggers Sept. 28, 2017, 9:25 p.m. UTC 
From: Eric Biggers <ebiggers@google.com>

When the file /proc/fs/fscache/objects (available with
CONFIG_FSCACHE_OBJECT_LIST=y) is opened, we request a user key with
description "fscache:objlist", then access its payload.  However, a
revoked key has a NULL payload, and we failed to check for this.
request_key() *does* skip revoked keys, but there is still a window
where the key can be revoked before we access its payload.

Fix it by checking for a NULL payload, treating it like a key which was
already revoked at the time it was requested.

Fixes: 4fbf4291aa15 ("FS-Cache: Allow the current state of all objects to be dumped")
Cc: <stable@vger.kernel.org>    [v2.6.32+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/fscache/object-list.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

James Morris Oct. 3, 2017, 10:51 a.m. UTC | #1 
On Thu, 28 Sep 2017, Eric Biggers wrote:

> From: Eric Biggers <ebiggers@google.com>
> 
> When the file /proc/fs/fscache/objects (available with
> CONFIG_FSCACHE_OBJECT_LIST=y) is opened, we request a user key with
> description "fscache:objlist", then access its payload.  However, a
> revoked key has a NULL payload, and we failed to check for this.
> request_key() *does* skip revoked keys, but there is still a window
> where the key can be revoked before we access its payload.
> 
> Fix it by checking for a NULL payload, treating it like a key which was
> already revoked at the time it was requested.
> 
> Fixes: 4fbf4291aa15 ("FS-Cache: Allow the current state of all objects to be dumped")
> Cc: <stable@vger.kernel.org>    [v2.6.32+]
> Signed-off-by: Eric Biggers <ebiggers@google.com>


Reviewed-by: James Morris <james.l.morris@oracle.com>
diff mbox

Patch

diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index b5ab06fabc60..0438d4cd91ef 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -331,6 +331,13 @@  static void fscache_objlist_config(struct fscache_objlist_data *data)
 	rcu_read_lock();
 
 	confkey = user_key_payload_rcu(key);
+	if (!confkey) {
+		/* key was revoked */
+		rcu_read_unlock();
+		key_put(key);
+		goto no_config;
+	}
+
 	buf = confkey->data;
 
 	for (len = confkey->datalen - 1; len >= 0; len--) {