Patchwork tcp: protect sysctl_tcp_cookie_size reads

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Submitter Eric Dumazet
Date Dec. 7, 2010, 10:20 p.m.
Message ID <1291760447.5324.31.camel@edumazet-laptop>
Download mbox | patch
Permalink /patch/74607/
State Accepted
Delegated to: David Miller
Headers show

Comments

Eric Dumazet - Dec. 7, 2010, 10:20 p.m.
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>
---
 net/ipv4/tcp_output.c |   27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)



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David Miller - Dec. 8, 2010, 8:35 p.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 07 Dec 2010 23:20:47 +0100

> 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>

Applied.
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Patch

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 05b1ecf..8cecb30 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -386,27 +386,30 @@  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.