From f19872575ff7819a3723154657a497d9bca66b33 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 7 Dec 2010 12:20:47 +0000 Subject: [PATCH] tcp: protect sysctl_tcp_cookie_size reads 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 Cc: Ben Hutchings Cc: William Allen Simpson Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 0d4a3cebfb46..61c2463e2753 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -385,27 +385,30 @@ 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. -- 2.20.1