[PATCH] SCTP: Fix sctp_auth_asoc_get_hmac() to avoid kernel panic

[Wei Yongjun <yjwei@cn.fujitsu.com>]

If association is setup with HMAC-ALGO parameter in which there is no 
HMAC algorithm supported by the endpoint, send a chunk with AUTH will 
cause kernel panic.

This is because  when send chunk with AUTH, sctp_auth_asoc_get_hmac() 
will be used to get the hmac. In this function, if the HMAC-ALGO is 
empty, it return NULL. If is not empty, it will find a valid hmac for 
using. But if all of the HMAC-ALGOs is not supported by endpoint, it 
will return a bogus pointer, not expected NULL pointer.

This patch fix this problem.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>

--- a/net/sctp/auth.c	2008-02-11 17:14:05.000000000 -0500
+++ b/net/sctp/auth.c	2008-02-14 02:01:18.000000000 -0500
@@ -549,13 +549,10 @@ struct sctp_hmac *sctp_auth_asoc_get_hma
 		if (!sctp_hmac_list[id].hmac_name)
 			continue;
 
-		break;
+		return &sctp_hmac_list[id];
 	}
 
-	if (id == 0)
-		return NULL;
-
-	return &sctp_hmac_list[id];
+	return NULL;
 }
 
 static int __sctp_auth_find_hmacid(__be16 *hmacs, int n_elts, __be16 hmac_id)