SCTP: Fix sctp_auth_asoc_get_hmac() to avoid kernel panic

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 <[email protected]>

net/sctp/auth.c 2008-02-14 02:01:18.000000000 -0500 renamed from net/sctp/auth.c 2008-02-11 17:14:05.000000000 -0500 +2 -5

@@ -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)

Hi Wei

Quoted 3 lines · Wei Yongjun

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 is a workaround, but this problem must never never happen.

RFC 4890 has the following text:

The HMAC algorithm based on SHA-1 MUST be supported and included in the HMAC-ALGO parameter.

As a result, we need to check in sctp_verify_param() that HMAC_SHA1 is present in the list. If not, we should probably treat this as a protocol violation.

It should also be a protocol violation if the HMAC parameter is empty.

That could almost remove the need for the sctp-auth_asoc_get_hmac() function.