Re: TCP-MD5 checksum failure on x86_64 SMP

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mardi 11 mai 2010 à 04:08 +0000, Bijay Singh a écrit :
> Hi Eric,
> 
> I guess that makes me the enviable one. So I am keen to test out this feature completely, as long as I know what to do as a next step, directions, patches.
> 
> Thanks


I believe third problem comes from commit 4957faad
(TCPCT part 1g: Responder Cookie => Initiator), from William Allen
Simpson.

When a SYN-ACK packet is built (in tcp_synack_options()),
it specifically forbids a TIMESTAMP option to be included if SACK is
also selected :

doing_ts &= !ireq->sack_ok;

Problem is this mask is done on a local variable. socket is still marked
as being timestamp enabled.


Later, when we build tcp options for data packets, we _include_ a
timestamp, while our SYNACK didnt mention the option.  

So the following trafic can happen (and fails) :

18:38:29.041966 IP 192.168.0.33.58906 > 192.168.0.56.22226: Flags [S], seq 4014064674, win 8860, options [mss 4430,sackOK,TS val 519041 ecr 0,nop,wscale 7,nop,nop,md5can't check - 9b44126367effcf3247fcbf6da76b24d], length 0
18:38:29.042072 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [S.], seq 586328714, ack 4014064675, win 5792, options [nop,nop,md5can't check - badd847799ded46f39642c341cc7e92b,mss 1460,nop,nop,sackOK,nop,wscale 7], length 0
18:38:29.042093 IP 192.168.0.33.58906 > 192.168.0.56.22226: Flags [.], ack 1, win 70, options [nop,nop,md5can't check - 3994ef6987df02a592963fba04c5d313], length 0
18:38:29.043217 IP 192.168.0.33.58906 > 192.168.0.56.22226: Flags [.], seq 1:1441, ack 1, win 70, options [nop,nop,md5can't check - 8399f7ccab3a6b8c5a3027ed58bba314], length 1440
18:38:29.043226 IP 192.168.0.33.58906 > 192.168.0.56.22226: Flags [P.], seq 1441:2501, ack 1, win 70, options [nop,nop,md5can't check - 701ebf65b1894a6bed4cefbf7a56596a], length 1060
18:38:29.043374 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [.], ack 1441, win 68, options [nop,nop,md5can't check - 1badb315ba436ab59bff5b37daa871be,nop,nop,TS val 113051377 ecr 519041], length 0
18:38:29.043383 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [.], ack 2501, win 91, options [nop,nop,md5can't check - 120564dcb99f822f3b70910282a6ed9d,nop,nop,TS val 113051377 ecr 519041], length 0
18:38:29.043673 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [.], seq 1:1429, ack 2501, win 91, options [nop,nop,md5can't check - fe5dfb438065373b52ba85bf800876a8,nop,nop,TS val 113051377 ecr 519041], length 1428
18:38:29.043681 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [P.], seq 1429:2500, ack 2501, win 91, options [nop,nop,md5can't check - 7a910cd5ff357bf0e2c8d3489aafaa86,nop,nop,TS val 113051377 ecr 519041], length 1071
18:38:32.037786 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [.], seq 1:1429, ack 2501, win 91, options [nop,nop,md5can't check - fe5dfb438065373b52ba85bf800876a8,nop,nop,TS val 113051677 ecr 519041], length 1428
18:38:38.037708 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [.], seq 1:1429, ack 2501, win 91, options [nop,nop,md5can't check - fe5dfb438065373b52ba85bf800876a8,nop,nop,TS val 113052277 ecr 519041], length 1428
18:38:50.037524 IP 192.168.0.56.22226 > 192.168.0.33.58906: Flags [.], seq 1:1429, ack 2501, win 91, options [nop,nop,md5can't check - fe5dfb438065373b52ba85bf800876a8,nop,nop,TS val 113053477 ecr 519041], length 1428


Could you try following patch ?

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5db3a2c..0be21cd 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -668,7 +668,7 @@ 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);
@@ -681,11 +681,12 @@ 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;