Date:	Fri, 18 Nov 2011 17:39:38 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nick Bowler <nbowler@...iptictech.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Timo Teras <timo.teras@....fi>
Subject: Re: Occasional oops with IPSec and IPv6.

Le vendredi 18 novembre 2011 à 11:27 -0500, Nick Bowler a écrit :
> On 2011-11-17 14:09 -0500, Nick Bowler wrote:
> > One of the tests we do with IPsec involves sending and receiving UDP
> > datagrams of all sizes from 1 to N bytes, where N is much larger than
> > the MTU.  In this particular instance, the MTU is 1500 bytes and N is
> > 10000 bytes.  This test works fine with IPv4, but I'm getting an
> > occasional oops on Linus' master with IPv6 (output at end of email).  We
> > also run the same test where N is less than the MTU, and it does not
> > trigger this issue.  The resulting fallout seems to eventually lock up
> > the box (although it continues to work for a little while afterwards).
> > 
> > The issue appears timing related, and it doesn't always occur.  This
> > probably also explains why I've not seen this issue before now, as we
> > recently upgraded all our lab systems to machines from this century
> > (with newfangled dual core processors).  This also makes it somewhat
> > hard to reproduce, but I can trigger it pretty reliably by running 'yes'
> > in an ssh session (which doesn't use IPsec) while running the test:
> > it'll usually trigger in 2 or 3 runs.  The choice of cipher suite
> > appears to be irrelevant.
> > 
> > I built a relatively old kernel (2.6.34) and could not reproduce the
> > issue there, so I ran a git bisect.  It pointed to the following, which
> > (unsurprisingly) no longer reverts cleanly.
> > 
> > Let me know if you need any more info.  I'll see if I can reproduce the
> > issue with a smaller test case...
> 
> OK, here's a somewhat straigthforward way to reproduce it that I've
> found.  It uses a short test program called "udp_burst" which simply
> transmits a bunch of UDP datagrams at all sizes between 1 and 10000,
> included at the end of this mail.
> 
>  * Build the test program
> 
>     % gcc -o udp_burst udp_burst.c
> 
>  * Setup transport mode IPv6 SAs between two hosts so that they can
>    communicate using IPsec.  Choose your favourite cipher suite.
>    In this example, my two hosts are "fec0::3/64" and "fec0::2/64": I
>    will be crashing the former.
> 
>    It can be reproduced with just one host transmitting to the bit
>    bucket, but it seems to go much faster with two.
> 
>  * Create some constant non-IPsec network traffic on the machine to be
>    crashed (for example, log in via SSH and run "yes").
>  
>  * On the machine to be crashed, run
> 
>     % while :; do ./udp_burst remote; done
> 
>    where remote is the other host (fec0::2 in my case).
>  
>  * Wait a few seconds and watch the fireworks.
> 
> % cat >udp_burst.c <<'EOF'
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <errno.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netdb.h>
> 
> #define MAX_DGRAM_SIZE 10000
> 
> static char buf[MAX_DGRAM_SIZE];
> 
> int main(int argc, char **argv)
> {
> 	char *addr = NULL, *port = "9000";
> 	struct addrinfo *info, hints = {
> 		.ai_family   = AF_UNSPEC,
> 		.ai_socktype = SOCK_DGRAM,
> 		.ai_flags    = AI_PASSIVE,
> 	};
> 	int i, rc, sock;
> 
> 	if (argc > 1)
> 		addr = argv[1];
> 	if (argc > 2)
> 		port = argv[2];
> 	if (!addr) {
> 		fprintf(stderr, "usage: %s addr [port]\n", argv[0]);
> 		return EXIT_FAILURE;
> 	}
> 
> 	rc = getaddrinfo(addr, port, &hints, &info);
> 	if (rc != 0) {
> 		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rc));
> 		return EXIT_FAILURE;
> 	}
> 
> 	sock = socket(info->ai_family, info->ai_socktype, info->ai_protocol);
> 	if (sock == -1) {
> 		perror("socket");
> 		return EXIT_FAILURE;
> 	}
> 
> 	if (connect(sock, info->ai_addr, info->ai_addrlen) == -1) {
> 		perror("connect");
> 		return EXIT_FAILURE;
> 	}
> 
> 	for (i = 0; i < MAX_DGRAM_SIZE; i++) {
> 		if (send(sock, buf, i+1, MSG_DONTWAIT) == -1) {
> 			if (errno != EAGAIN && errno != ECONNREFUSED) {
> 				perror("send");
> 			}
> 		}
> 	}
> 
> 	return 0;
> }
> EOF
> 

Please note commit 80c802f307 added a known bug, fixed in commit
0b150932197b (xfrm: avoid possible oopse in xfrm_alloc_dst)

Given commit 80c802f307 complexity, we can assume other bugs are to be
fixed as well.

Unfortunately, Timo seems unresponsive.



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