Re: [PATCH mptcp-net] selftests: mptcp: fix an UAF in mptcp_connect.c

August 14, 2026 at 4:54 PM, "Matthieu Baerts" <[email protected] mailto:[email protected]?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel.org%3E > wrote:



> > 
> This assumes peer == addr. It is certainly the case but it looks wrong,
> and I guess sashiko will complain like it did here.
> 
> We could add something on the commit message to say that it is always an IP address that is given, but maybe we should also just
> handle that correctly: either peer here is not a pointer, and the content
> is copied, 

I prefer this, because it is smaller, like:

'''
 static int sock_connect_mptcp(const char * const remoteaddr,
 			      const char * const port, int proto,
-			      struct addrinfo **peer,
+			      struct sockaddr_storage *peer, socklen_t *peer_len,
 			      int infd, struct wstate *winfo)
 {
 ...
-				*peer = a;
 				break;
...
-				*peer = a;
 				break;
...
+	if (sock != -1) {
+		memcpy(peer, a->ai_addr, a->ai_addrlen);
+		*peer_len = a->ai_addrlen;
+	}
 	freeaddrinfo(addr);
...

-	struct addrinfo *peer = NULL;
+	struct sockaddr_storage peer;
+	socklen_t peer_len;
...
-	fd = sock_connect_mptcp(..., &peer, fd_in, &winfo);
+	fd = sock_connect_mptcp(..., &peer, &peer_len, fd_in, &winfo);
...
-	if (connect(fd, peer->ai_addr, peer->ai_addrlen))
+	if (connect(fd, (struct sockaddr *)&peer, peer_len))
'''

> or you pass &addr to sock_connect_mptcp, and you do the free here.

This needs a refactor of sock_connect_mptcp – I used to do it that way. But I
worry that backporting could be tricky. If you're fine with it, I'm okay with this plan
as well.

WDYT?

Thanks
Gang