[patch 60/87] keys: Handle there being no fallback destination keyring for request_key()

[Greg KH]

2.6.29-stable review patch.  If anyone has any objections, please let us know.

------------------

From: David Howells <dhowells@xxxxxxxxxx>

commit 34574dd10b6d0697b86703388d6d6af9cbf4bb48 upstream.

When request_key() is called, without there being any standard process
keyrings on which to fall back if a destination keyring is not specified, an
oops is liable to occur when construct_alloc_key() calls down_write() on
dest_keyring's semaphore.

Due to function inlining this may be seen as an oops in down_write() as called
from request_key_and_link().

This situation crops up during boot, where request_key() is called from within
the kernel (such as in CIFS mounts) where nobody is actually logged in, and so
PAM has not had a chance to create a session keyring and user keyrings to act
as the fallback.

To fix this, make construct_alloc_key() not attempt to cache a key if there is
no fallback key if no destination keyring is given specifically.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Tested-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 security/keys/request_key.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -311,7 +311,8 @@ static int construct_alloc_key(struct ke
 
 	set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
 
-	down_write(&dest_keyring->sem);
+	if (dest_keyring)
+		down_write(&dest_keyring->sem);
 
 	/* attach the key to the destination keyring under lock, but we do need
 	 * to do another check just in case someone beat us to it whilst we
@@ -322,10 +323,12 @@ static int construct_alloc_key(struct ke
 	if (!IS_ERR(key_ref))
 		goto key_already_present;
 
-	__key_link(dest_keyring, key);
+	if (dest_keyring)
+		__key_link(dest_keyring, key);
 
 	mutex_unlock(&key_construction_mutex);
-	up_write(&dest_keyring->sem);
+	if (dest_keyring)
+		up_write(&dest_keyring->sem);
 	mutex_unlock(&user->cons_lock);
 	*_key = key;
 	kleave(" = 0 [%d]", key_serial(key));


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/