Commit a32aee8f authored by Jiayuan Chen's avatar Jiayuan Chen Committed by Martin KaFai Lau
Browse files

bpf: fix filed access without lock 



The tcp_bpf_recvmsg_parser() function, running in user context,
retrieves seq_copied from tcp_sk without holding the socket lock, and
stores it in a local variable seq. However, the softirq context can
modify tcp_sk->seq_copied concurrently, for example, n tcp_read_sock().

As a result, the seq value is stale when it is assigned back to
tcp_sk->copied_seq at the end of tcp_bpf_recvmsg_parser(), leading to
incorrect behavior.

Due to concurrency, the copied_seq field in tcp_bpf_recvmsg_parser()
might be set to an incorrect value (less than the actual copied_seq) at
the end of function: 'WRITE_ONCE(tcp->copied_seq, seq)'. This causes the
'offset' to be negative in tcp_read_sock()->tcp_recv_skb() when
processing new incoming packets (sk->copied_seq - skb->seq becomes less
than 0), and all subsequent packets will be dropped.

Signed-off-by: default avatarJiayuan Chen <mrpre@163.com>
Link: https://lore.kernel.org/r/20241028065226.35568-1-mrpre@163.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent 740be3b9

net/ipv4/tcp_bpf.c

+4 −3
Original line number Diff line number Diff line
@@ -221,11 +221,11 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, 
				  int flags,

				  int *addr_len)

{

	struct tcp_sock *tcp = tcp_sk(sk);

	int peek = flags & MSG_PEEK;

	u32 seq = tcp->copied_seq;

	struct sk_psock *psock;

	struct tcp_sock *tcp;

	int copied = 0;

	u32 seq;



	if (unlikely(flags & MSG_ERRQUEUE))

		return inet_recv_error(sk, msg, len, addr_len);
@@ -238,7 +238,8 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, 
		return tcp_recvmsg(sk, msg, len, flags, addr_len);



	lock_sock(sk);



	tcp = tcp_sk(sk);

	seq = tcp->copied_seq;

	/* We may have received data on the sk_receive_queue pre-accept and

	 * then we can not use read_skb in this context because we haven't

	 * assigned a sk_socket yet so have no link to the ops. The work-around