Re: TCP-MD5 checksum failure on x86_64 SMP

Stephen Hemminger
2010-05-17T20:42:43Z

On Mon, 17 May 2010 07:03:49 +0200
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Le lundi 17 mai 2010 à 03:49 +0000, Bijay Singh a écrit :
>
> > I am on quite an old kernel 2.6.27 and could not apply your patches.
> >
> > Then i moved on to the kernel 2.6.32.11 however since then I have not been able to bring up my card, this is something i need to fix before i can test you fix. Working on that.
> >
>
> Thanks again for the status report.
>
> I see bug is older than what I stated in my previous mail
>
> I could reproduce it in my lab and confirm following patch fixes it
>
> This is a stable candidate (2.6.27 kernels)
>
> Thanks
>
> [PATCH] tcp: tcp_synack_options() fix
>
> Commit 33ad798c924b4a (tcp: options clean up) introduced a problem
> if MD5+SACK+timestamps were used in initial SYN message.
>
> Some stacks (old linux for example) try to negotiate MD5+SACK+TSTAMP
> sessions, but since 20 bytes of tcp options space are not enough to
> store all the bits needed, we chose to disable timestamps in this case.
>
> We send a SYN-ACK _without_ timestamp option, but socket has timestamps
> enabled and all further outgoing messages contain a TS block, all with
> the initial timestamp of the remote peer.
>
> Fix is to really disable timestamps option for the whole session.
>
> Reported-by: Bijay Singh <Bijay.Singh@guavus.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> ---
> net/ipv4/tcp_output.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 0dda86e..b8bb226 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -667,7 +667,7 @@ static unsigned tcp_synack_options(struct sock *sk,
> u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
> xvp->cookie_plus :
> 0;
> - bool doing_ts = ireq->tstamp_ok;
> + bool doing_ts;
>
> #ifdef CONFIG_TCP_MD5SIG
> *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
> @@ -680,11 +680,12 @@ static unsigned tcp_synack_options(struct sock *sk,
> * rather than TS in order to fit in better with old,
> * buggy kernels, but that was deemed to be unnecessary.
> */
> - doing_ts &= !ireq->sack_ok;
> + ireq->tstamp_ok &= !ireq->sack_ok;
> }
> #else
> *md5 = NULL;
> #endif
> + doing_ts = ireq->tstamp_ok;
>
> /* We always send an MSS option. */
> opts->mss = mss;
>
>

Since you are doing away with flag variable, why not this instead?

--- a/net/ipv4/tcp_output.c 2010-05-17 13:38:32.822025583 -0700
+++ b/net/ipv4/tcp_output.c 2010-05-17 13:41:47.321734775 -0700
@@ -668,7 +668,6 @@ static unsigned tcp_synack_options(struc
u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
xvp->cookie_plus :
0;
- bool doing_ts = ireq->tstamp_ok;

#ifdef CONFIG_TCP_MD5SIG
*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
@@ -681,7 +680,7 @@ static unsigned tcp_synack_options(struc
* rather than TS in order to fit in better with old,
* buggy kernels, but that was deemed to be unnecessary.
*/
- doing_ts &= !ireq->sack_ok;
+ ireq->tstamp_ok &= !ireq->sack_ok;
}
#else
*md5 = NULL;
@@ -696,7 +695,7 @@ static unsigned tcp_synack_options(struc
opts->options |= OPTION_WSCALE;
remaining -= TCPOLEN_WSCALE_ALIGNED;
}
- if (likely(doing_ts)) {
+ if (likely(ireq->tstamp_ok)) {
opts->options |= OPTION_TS;
opts->tsval = TCP_SKB_CB(skb)->when;
opts->tsecr = req->ts_recent;
@@ -704,7 +703,7 @@ static unsigned tcp_synack_options(struc
}
if (likely(ireq->sack_ok)) {
opts->options |= OPTION_SACK_ADVERTISE;
- if (unlikely(!doing_ts))
+ if (unlikely(!ireq->tstamp_ok))
remaining -= TCPOLEN_SACKPERM_ALIGNED;
}

@@ -712,7 +711,7 @@ static unsigned tcp_synack_options(struc
* If the <SYN> options fit, the same options should fit now!
*/
if (*md5 == NULL &&
- doing_ts &&
+ ireq->tstamp_ok &&
cookie_plus > TCPOLEN_COOKIE_BASE) {
int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */

--