mptcp: fix NULL ptr dereference in MP_JOIN error path (39884604) · Commits · 戴 / test

When token lookup on MP_JOIN 3rd ack fails, the server socket closes with a reset the incoming child. Such socket has the 'is_mptcp' flag set, but no msk socket associated - due to the failed lookup. While crafting the reset packet mptcp_established_options_mp() will try to dereference the child's master socket, causing a NULL ptr dereference. This change addresses the issue with explicit fallback to TCP in such error path. Fixes: ("mptcp: cope better with MP_JOIN failure") Signed-off-by:

Paolo Abeni <pabeni@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/mptcp/subflow.c

+16 −4

Original line number	Diff line number	Diff line
		@@ -413,6 +413,20 @@ static void subflow_ulp_fallback(struct sock *sk,
		tcp_sk(sk)->is_mptcp = 0;
		}

		static void subflow_drop_ctx(struct sock *ssk)
		{
		struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(ssk);

		if (!ctx)
		return;

		subflow_ulp_fallback(ssk, ctx);
		if (ctx->conn)
		sock_put(ctx->conn);

		kfree_rcu(ctx, rcu);
		}

		static struct sock subflow_syn_recv_sock(const struct sock sk,
		struct sk_buff *skb,
		struct request_sock *req,
		@@ -485,10 +499,7 @@ create_child:
		if (fallback_is_fatal)
		goto dispose_child;

		if (ctx) {
		subflow_ulp_fallback(child, ctx);
		kfree_rcu(ctx, rcu);
		}
		subflow_drop_ctx(child);
		goto out;
		}

		@@ -537,6 +548,7 @@ out:
		return child;

		dispose_child:
		subflow_drop_ctx(child);
		tcp_rsk(req)->drop_req = true;
		tcp_send_active_reset(child, GFP_ATOMIC);
		inet_csk_prepare_for_destroy_sock(child);

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