[PATCH] dm-crypt: check key payload pointer not null

[Ondrej Kozina <okozina@redhat.com>]

Hi Mike,

those are fixes for latest version (including your cleanup patch). I've fixed one
awkward bug the rest is based on David's sugestions he gave me earlier today.

David, may I also kindly ask you for oficial 'Reviewed-by' stamp provided 
it's correct now (with regard to kernel keyring bits)?

bugfix: harden checks for 'user' or 'logon' keywords in key_string (it allowed
to pass with :logo:... or "use:...)

bugfix: we have to check user_key_payload reference after rcu_read_lock().
Otherwise keys revoked between request_key() and rcu_read_lock() calls would
return NULL pointer.

improvement: calling key_validate() right after request_key() is
useless. Exactly same check is performed inside request_key()
routine.

improvement: do not check the whole key_type string again. We already know
it's either 'logon' or 'user'. Read just first char.
---
 drivers/md/dm-crypt.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index c6ff083..78ab5e8 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1501,31 +1501,31 @@ static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_string
 	if (!key_desc || key_desc == key_string || !strlen(key_desc + 1))
 		return -EINVAL;
 
-	if (strncmp(key_string, "logon", key_desc - key_string) &&
-	    strncmp(key_string, "user", key_desc - key_string))
+	if (strncmp(key_string, "logon:", key_desc - key_string + 1) &&
+	    strncmp(key_string, "user:", key_desc - key_string + 1))
 		return -EINVAL;
 
 	new_key_string = kstrdup(key_string, GFP_KERNEL);
 	if (!new_key_string)
 		return -ENOMEM;
 
-	key = request_key(strncmp(key_string, "user", 4) ? &key_type_logon : &key_type_user,
+	key = request_key(key_string[0] == 'l' ? &key_type_logon : &key_type_user,
 			  key_desc + 1, NULL);
 	if (IS_ERR(key)) {
 		kzfree(new_key_string);
 		return PTR_ERR(key);
 	}
 
-	ret = key_validate(key);
-	if (ret < 0) {
+	rcu_read_lock();
+
+	ukp = user_key_payload(key);
+	if (!ukp) {
+		rcu_read_unlock();
 		key_put(key);
 		kzfree(new_key_string);
-		return ret;
+		return -EKEYREVOKED;
 	}
 
-	rcu_read_lock();
-
-	ukp = user_key_payload(key);
 	if (cc->key_size != ukp->datalen) {
 		rcu_read_unlock();
 		key_put(key);
-- 
2.7.4