From: Liu Jian liujian56@huawei.com
commit cd9733f5d75c94a32544d6ce5be47e14194cf137 upstream.
With two Msgs, msgA and msgB and a user doing nonblocking sendmsg calls (or multiple cores) on a single socket 'sk' we could get the following flow.
msgA, sk msgB, sk ----------- --------------- tcp_bpf_sendmsg() lock(sk) psock = sk->psock tcp_bpf_sendmsg() lock(sk) ... blocking tcp_bpf_send_verdict if (psock->eval == NONE) psock->eval = sk_psock_msg_verdict .. < handle SK_REDIRECT case > release_sock(sk) < lock dropped so grab here > ret = tcp_bpf_sendmsg_redir psock = sk->psock tcp_bpf_send_verdict lock_sock(sk) ... blocking on B if (psock->eval == NONE) <- boom. psock->eval will have msgA state
The problem here is we dropped the lock on msgA and grabbed it with msgB. Now we have old state in psock and importantly psock->eval has not been cleared. So msgB will run whatever action was done on A and the verdict program may never see it.
Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface") Signed-off-by: Liu Jian liujian56@huawei.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: John Fastabend john.fastabend@gmail.com Link: https://lore.kernel.org/bpf/20211012052019.184398-1-liujian56@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_bpf.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
--- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -313,6 +313,7 @@ static int tcp_bpf_send_verdict(struct s bool cork = false, enospc = sk_msg_full(msg); struct sock *sk_redir; u32 tosend, delta = 0; + u32 eval = __SK_NONE; int ret;
more_data: @@ -356,13 +357,24 @@ more_data: case __SK_REDIRECT: sk_redir = psock->sk_redir; sk_msg_apply_bytes(psock, tosend); + if (!psock->apply_bytes) { + /* Clean up before releasing the sock lock. */ + eval = psock->eval; + psock->eval = __SK_NONE; + psock->sk_redir = NULL; + } if (psock->cork) { cork = true; psock->cork = NULL; } sk_msg_return(sk, msg, tosend); release_sock(sk); + ret = tcp_bpf_sendmsg_redir(sk_redir, msg, tosend, flags); + + if (eval == __SK_REDIRECT) + sock_put(sk_redir); + lock_sock(sk); if (unlikely(ret < 0)) { int free = sk_msg_free_nocharge(sk, msg);