Commit 18f02ad1 authored Apr 26, 2020 by Xiyu Yang Committed by Daniel Borkmann Apr 27, 2020

bpf: Fix sk_psock refcnt leak when receiving message

tcp_bpf_recvmsg() invokes sk_psock_get(), which returns a reference of
the specified sk_psock object to "psock" with increased refcnt.

When tcp_bpf_recvmsg() returns, local variable "psock" becomes invalid,
so the refcount should be decreased to keep refcount balanced.

The reference counting issue happens in several exception handling paths
of tcp_bpf_recvmsg(). When those error scenarios occur such as "flags"
includes MSG_ERRQUEUE, the function forgets to decrease the refcnt
increased by sk_psock_get(), causing a refcnt leak.

Fix this issue by calling sk_psock_put() or pulling up the error queue
read handling when those error scenarios occur.

Fixes: e7a5f1f1 ("bpf/sockmap: Read psock ingress_msg before sk_receive_queue")
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/1587872115-42805-1-git-send-email-xiyuyang19@fudan.edu.cn

parent 37255e7a

net/ipv4/tcp_bpf.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -262,14 +262,17 @@ static int tcp_bpf_recvmsg(struct sock sk, struct msghdr msg, size_t len,
		struct sk_psock *psock;
		int copied, ret;

		if (unlikely(flags & MSG_ERRQUEUE))
		return inet_recv_error(sk, msg, len, addr_len);

		psock = sk_psock_get(sk);
		if (unlikely(!psock))
		return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
		if (unlikely(flags & MSG_ERRQUEUE))
		return inet_recv_error(sk, msg, len, addr_len);
		if (!skb_queue_empty(&sk->sk_receive_queue) &&
		sk_psock_queue_empty(psock))
		sk_psock_queue_empty(psock)) {
		sk_psock_put(sk, psock);
		return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
		}
		lock_sock(sk);
		msg_bytes_ready:
		copied = __tcp_bpf_recvmsg(sk, psock, msg, len, flags);

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