This is a note to let you know that I've just added the patch titled
tcp: sysctl: Fix a race to avoid unexpected 0 window from space
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-sysctl-fix-a-race-to-avoid-unexpected-0-window-from-space.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Mon Mar 19 10:11:52 CET 2018
From: Gao Feng <fgao@xxxxxxxxxx>
Date: Fri, 24 Mar 2017 07:05:12 +0800
Subject: tcp: sysctl: Fix a race to avoid unexpected 0 window from space
From: Gao Feng <fgao@xxxxxxxxxx>
[ 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 <fgao@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/net/tcp.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1099,9 +1099,11 @@ void tcp_select_initial_window(int __spa
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 */
Patches currently in stable-queue which might be from fgao@xxxxxxxxxx are
queue-3.18/tcp-sysctl-fix-a-race-to-avoid-unexpected-0-window-from-space.patch