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Date: Fri, 29 Jul 2016 09:34:02 -0400 From: Soheil Hassas Yeganeh <soheil.kdev@...il.com> To: davem@...emloft.net, netdev@...r.kernel.org Cc: edumazet@...gle.com, ycheng@...gle.com, ncardwell@...gle.com, Soheil Hassas Yeganeh <soheil@...gle.com> Subject: [PATCH v2 net] tcp: consider recv buf for the initial window scale From: Soheil Hassas Yeganeh <soheil@...gle.com> tcp_select_initial_window() intends to advertise a window scaling for the maximum possible window size. To do so, it considers the maximum of net.ipv4.tcp_rmem[2] and net.core.rmem_max as the only possible upper-bounds. However, users with CAP_NET_ADMIN can use SO_RCVBUFFORCE to set the socket's receive buffer size to values larger than net.ipv4.tcp_rmem[2] and net.core.rmem_max. Thus, SO_RCVBUFFORCE is effectively ignored by tcp_select_initial_window(). To fix this, consider the maximum of net.ipv4.tcp_rmem[2], net.core.rmem_max and socket's initial buffer space. Fixes: b0573dea1fb3 ("[NET]: Introduce SO_{SND,RCV}BUFFORCE socket options") Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com> Suggested-by: Neal Cardwell <ncardwell@...gle.com> --- net/ipv4/tcp_output.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index b26aa87..bdaef7f 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -236,7 +236,8 @@ void tcp_select_initial_window(int __space, __u32 mss, /* Set window scaling on max possible window * See RFC1323 for an explanation of the limit to 14 */ - space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max); + space = max_t(u32, space, sysctl_tcp_rmem[2]); + space = max_t(u32, space, sysctl_rmem_max); space = min_t(u32, space, *window_clamp); while (space > 65535 && (*rcv_wscale) < 14) { space >>= 1; -- 2.8.0.rc3.226.g39d4020
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