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FS-Cache: fix dereference of NULL user_key_payload

commit d124b2c53c upstream.

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>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
master
Eric Biggers 4 years ago
committed by Greg Kroah-Hartman
parent
commit
d2d576e285
  1. 7
      fs/fscache/object-list.c

7
fs/fscache/object-list.c

@ -330,6 +330,13 @@ static void fscache_objlist_config(struct fscache_objlist_data *data)
rcu_read_lock();
confkey = user_key_payload(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/* key was revoked */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--) {

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