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FS-Cache: fix dereference of NULL user_key_payload

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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: 4fbf4291aa ("FS-Cache: Allow the current state of all objects to be dumped")
Reviewed-by: James Morris <james.l.morris@oracle.com>
Cc: <stable@vger.kernel.org>    [v2.6.32+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
Eric Biggers 2017-10-09 12:40:00 -07:00 committed by David Howells
parent 13923d0865
commit d124b2c53c
1 changed files with 7 additions and 0 deletions
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7
fs/fscache/object-list.c
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@ -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/* key was revoked */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--) {