xfrm_user: propagate sec ctx allocation errors

When we fail to attach the security context in xfrm_state_construct()
we'll return 0 as error value which, in turn, will wrongly claim success
to userland when, in fact, we won't be adding / updating the XFRM state.

This is a regression introduced by commit fd21150a0f ("[XFRM] netlink:
Inline attach_encap_tmpl(), attach_sec_ctx(), and attach_one_addr()").

Fix it by propagating the error returned by security_xfrm_state_alloc()
in this case.

Fixes: fd21150a0f ("[XFRM] netlink: Inline attach_encap_tmpl()...")
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_user.c

@@ -581,9 +581,12 @@ static struct xfrm_state *xfrm_state_construct(struct net *net,
 	if (err)
 		goto error;
 
-	if (attrs[XFRMA_SEC_CTX] &&
-	    security_xfrm_state_alloc(x, nla_data(attrs[XFRMA_SEC_CTX])))
-		goto error;
+	if (attrs[XFRMA_SEC_CTX]) {
+		err = security_xfrm_state_alloc(x,
+						nla_data(attrs[XFRMA_SEC_CTX]));
+		if (err)
+			goto error;
+	}
 
 	if ((err = xfrm_alloc_replay_state_esn(&x->replay_esn, &x->preplay_esn,
 					       attrs[XFRMA_REPLAY_ESN_VAL])))