From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 7 Dec 2010 12:20:47 +0000 (+0000)
Subject: tcp: protect sysctl_tcp_cookie_size reads
X-Git-Tag: firefly_0821_release~9833^2~71^2^2~94
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=2efb9908d6ac415d69b2688b684799c51eb844fd;p=firefly-linux-kernel-4.4.55.git

tcp: protect sysctl_tcp_cookie_size reads

[ Upstream commit f19872575ff7819a3723154657a497d9bca66b33 ]

Make sure sysctl_tcp_cookie_size is read once in
tcp_cookie_size_check(), or we might return an illegal value to caller
if sysctl_tcp_cookie_size is changed by another cpu.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: William Allen Simpson <william.allen.simpson@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e1fafbbe91ae..7abecf73add9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -391,27 +391,30 @@ struct tcp_out_options {
  */
 static u8 tcp_cookie_size_check(u8 desired)
 {
-	if (desired > 0) {
+	int cookie_size;
+
+	if (desired > 0)
 		/* previously specified */
 		return desired;
-	}
-	if (sysctl_tcp_cookie_size <= 0) {
+
+	cookie_size = ACCESS_ONCE(sysctl_tcp_cookie_size);
+	if (cookie_size <= 0)
 		/* no default specified */
 		return 0;
-	}
-	if (sysctl_tcp_cookie_size <= TCP_COOKIE_MIN) {
+
+	if (cookie_size <= TCP_COOKIE_MIN)
 		/* value too small, specify minimum */
 		return TCP_COOKIE_MIN;
-	}
-	if (sysctl_tcp_cookie_size >= TCP_COOKIE_MAX) {
+
+	if (cookie_size >= TCP_COOKIE_MAX)
 		/* value too large, specify maximum */
 		return TCP_COOKIE_MAX;
-	}
-	if (0x1 & sysctl_tcp_cookie_size) {
+
+	if (cookie_size & 1)
 		/* 8-bit multiple, illegal, fix it */
-		return (u8)(sysctl_tcp_cookie_size + 0x1);
-	}
-	return (u8)sysctl_tcp_cookie_size;
+		cookie_size++;
+
+	return (u8)cookie_size;
 }
 
 /* Write previously computed TCP options to the packet.