From 867f816badc01e6da655028810d468c9f935b37c Mon Sep 17 00:00:00 2001 From: Soheil Hassas Yeganeh Date: Fri, 8 Jun 2018 22:47:10 -0400 Subject: [PATCH] tcp: limit sk_rcvlowat by the maximum receive buffer The user-provided value to setsockopt(SO_RCVLOWAT) can be larger than the maximum possible receive buffer. Such values mute POLLIN signals on the socket which can stall progress on the socket. Limit the user-provided value to half of the maximum receive buffer, i.e., half of sk_rcvbuf when the receive buffer size is set by the user, or otherwise half of sysctl_tcp_rmem[2]. Fixes: d1361840f8c5 ("tcp: fix SO_RCVLOWAT and RCVBUF autotuning") Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Eric Dumazet Reviewed-by: Neal Cardwell Acked-by: Willem de Bruijn Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 2741953adaba..141acd92e58a 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1694,6 +1694,13 @@ EXPORT_SYMBOL(tcp_peek_len); /* Make sure sk_rcvbuf is big enough to satisfy SO_RCVLOWAT hint */ int tcp_set_rcvlowat(struct sock *sk, int val) { + int cap; + + if (sk->sk_userlocks & SOCK_RCVBUF_LOCK) + cap = sk->sk_rcvbuf >> 1; + else + cap = sock_net(sk)->ipv4.sysctl_tcp_rmem[2] >> 1; + val = min(val, cap); sk->sk_rcvlowat = val ? : 1; /* Check if we need to signal EPOLLIN right now */ @@ -1702,12 +1709,7 @@ int tcp_set_rcvlowat(struct sock *sk, int val) if (sk->sk_userlocks & SOCK_RCVBUF_LOCK) return 0; - /* val comes from user space and might be close to INT_MAX */ val <<= 1; - if (val < 0) - val = INT_MAX; - - val = min(val, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]); if (val > sk->sk_rcvbuf) { sk->sk_rcvbuf = val; tcp_sk(sk)->window_clamp = tcp_win_from_space(sk, val); -- 2.11.0