From 37633f021b7f88a003ef57b334c9ac31509e89f9 Mon Sep 17 00:00:00 2001 From: Gao Feng Date: Fri, 24 Mar 2017 07:05:12 +0800 Subject: tcp: sysctl: Fix a race to avoid unexpected 0 window from space [ Upstream commit c48367427a39ea0b85c7cf018fe4256627abfd9e ] Because sysctl_tcp_adv_win_scale could be changed any time, so there is one race in tcp_win_from_space. For example, 1.sysctl_tcp_adv_win_scale<=0 (sysctl_tcp_adv_win_scale is negative now) 2.space>>(-sysctl_tcp_adv_win_scale) (sysctl_tcp_adv_win_scale is postive now) As a result, tcp_win_from_space returns 0. It is unexpected. Certainly if the compiler put the sysctl_tcp_adv_win_scale into one register firstly, then use the register directly, it would be ok. But we could not depend on the compiler behavior. Signed-off-by: Gao Feng Signed-off-by: David S. Miller Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- include/net/tcp.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'include') diff --git a/include/net/tcp.h b/include/net/tcp.h index cecb0e0eff06..a3696b778757 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1199,9 +1199,11 @@ void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd, static inline int tcp_win_from_space(int space) { - return sysctl_tcp_adv_win_scale<=0 ? - (space>>(-sysctl_tcp_adv_win_scale)) : - space - (space>>sysctl_tcp_adv_win_scale); + int tcp_adv_win_scale = sysctl_tcp_adv_win_scale; + + return tcp_adv_win_scale <= 0 ? + (space>>(-tcp_adv_win_scale)) : + space - (space>>tcp_adv_win_scale); } /* Note: caller must be prepared to deal with negative returns */ -- cgit v1.2.3