Date:	Mon, 1 Jul 2013 01:23:08 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Dave Jones <davej@...hat.com>, netdev@...r.kernel.org
Subject: Re: skbuff: skb_under_panic warning in 3.10rc7+

On Mon, Jul 01, 2013 at 12:13:22AM +0200, Hannes Frederic Sowa wrote:
> On Sun, Jun 30, 2013 at 12:02:46PM -0400, Dave Jones wrote:
> > skbuff: skb_under_panic: text:ffffffff816765f6 len:48 put:40 head:ffff88013deb6df0 data:ffff88013deb6dec tail:0x2c end:0xc0 dev:<NULL>
> > ------------[ cut here ]------------
> > kernel BUG at net/core/skbuff.c:126!
> > invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> > Modules linked in: dccp_ipv4 dccp 8021q garp bridge stp dlci mpoa snd_seq_dummy sctp fuse hidp tun bnep nfnetlink scsi_transport_iscsi rfcomm can_raw can_bcm af_802154 appletalk caif_socket can caif ipt_ULOG x25 rose af_key pppoe pppox ipx phonet irda llc2 ppp_generic slhc p8023 psnap p8022 llc crc_ccitt atm bluetooth netrom ax25 nfc rfkill rds af_rxrpc coretemp hwmon kvm_intel kvm crc32c_intel snd_hda_codec_realtek ghash_clmulni_intel microcode pcspkr snd_hda_codec_hdmi snd_hda_intel snd_hda_codec snd_hwdep usb_debug snd_seq snd_seq_device snd_pcm e1000e snd_page_alloc snd_timer ptp snd pps_core soundcore xfs libcrc32c
> > CPU: 2 PID: 8095 Comm: trinity-child2 Not tainted 3.10.0-rc7+ #37 
> > task: ffff8801f52c2520 ti: ffff8801e6430000 task.ti: ffff8801e6430000
> > RIP: 0010:[<ffffffff816e759c>]  [<ffffffff816e759c>] skb_panic+0x63/0x65
> > RSP: 0018:ffff8801e6431de8  EFLAGS: 00010282
> > RAX: 0000000000000086 RBX: ffff8802353d3cc0 RCX: 0000000000000006
> > RDX: 0000000000003b90 RSI: ffff8801f52c2ca0 RDI: ffff8801f52c2520
> > RBP: ffff8801e6431e08 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000001 R11: 0000000000000001 R12: ffff88022ea0c800
> > R13: ffff88022ea0cdf8 R14: ffff8802353ecb40 R15: ffffffff81cc7800
> > FS:  00007f5720a10740(0000) GS:ffff880244c00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000005862000 CR3: 000000022843c000 CR4: 00000000001407e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
> > Stack:
> >  ffff88013deb6dec 000000000000002c 00000000000000c0 ffffffff81a3f6e4
> >  ffff8801e6431e18 ffffffff8159a9aa ffff8801e6431e90 ffffffff816765f6
> >  ffffffff810b756b 0000000700000002 ffff8801e6431e40 0000fea9292aa8c0
> > Call Trace:
> >  [<ffffffff8159a9aa>] skb_push+0x3a/0x40
> >  [<ffffffff816765f6>] ip6_push_pending_frames+0x1f6/0x4d0
> >  [<ffffffff810b756b>] ? mark_held_locks+0xbb/0x140
> >  [<ffffffff81694919>] udp_v6_push_pending_frames+0x2b9/0x3d0
> >  [<ffffffff81694660>] ? udplite_getfrag+0x20/0x20
> >  [<ffffffff8162092a>] udp_lib_setsockopt+0x1aa/0x1f0
> >  [<ffffffff811cc5e7>] ? fget_light+0x387/0x4f0
> >  [<ffffffff816958a4>] udpv6_setsockopt+0x34/0x40
> >  [<ffffffff815949f4>] sock_common_setsockopt+0x14/0x20
> >  [<ffffffff81593c31>] SyS_setsockopt+0x71/0xd0
> >  [<ffffffff816f5d54>] tracesys+0xdd/0xe2
> > Code: 00 00 48 89 44 24 10 8b 87 d8 00 00 00 48 89 44 24 08 48 8b 87 e8 00 00 00 48 c7 c7 c0 04 aa 81 48 89 04 24 31 c0 e8 e1 7e ff ff <0f> 0b 55 48 89 e5 0f 0b 55 48 89 e5 0f 0b 55 48 89 e5 0f 0b 55 
> > RIP  [<ffffffff816e759c>] skb_panic+0x63/0x65
> >  RSP <ffff8801e6431de8>
> 
> Dave, could you try to reproduce this Eric's patch
> 
> https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/net/ipv6/ip6_output.c?id=284041ef21fdf2e0d216ab6b787bc9072b4eb58a
> 
> cherry-picked from net-next? I could just test net-next with my testcase and
> at least my BUG does not occur any more.

Sorry, I am a bit too tired. The patch is already in net. I could again
reproduce at least my crash with net-next, it just needs a bit more load
and retries to do so. I do think those BUGs are somehow connected.

Here is my test program:

-- 8< --

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <linux/udp.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

int main(int argc, char **argv)
{
	int on = 1;
	int mtu = 1280;
	char buf[1220] = {0};
	
	int sockfd = socket(AF_INET6, SOCK_DGRAM, 0);
	if (sockfd < 0) {
		perror("socket");
		exit(EXIT_FAILURE);
	}
	
	if (setsockopt(sockfd, IPPROTO_UDP, UDP_CORK, &on, sizeof(on))) {
		perror("setsockopt");
		exit(EXIT_FAILURE);
	}
	
	if (setsockopt(sockfd, IPPROTO_IPV6, IPV6_MTU, &mtu, sizeof(mtu))) {
		perror("setsockopt");
		exit(EXIT_FAILURE);
	}
	
	
	struct sockaddr_in6 sa6 = {0};
	sa6.sin6_family = AF_INET6;
	sa6.sin6_port = 678;
	if (!inet_pton(AF_INET6, "::1", &sa6.sin6_addr)) {
		perror("inet_pton");
		exit(EXIT_FAILURE);
	}
	
	while (true) {
		const char dstops[8] = {0};
		if (setsockopt(sockfd, IPPROTO_IPV6, IPV6_DSTOPTS, &dstops, sizeof(dstops))) {
			perror("setsockopt");
			exit(EXIT_FAILURE);
		}
		
		if (sendto(sockfd, buf, sizeof(buf), MSG_MORE, (struct sockaddr *)&sa6,
				sizeof(sa6)) == -1) {
			perror("sendto");
			exit(EXIT_FAILURE);
		}
	}
	
	if (close(sockfd)) {
		perror("close");
		exit(EXIT_FAILURE);
	}
}

-- >8 --

What is a bit strange but I did not investiage, yet:

If the size of buf is strict smaller than 1217 I get a message too big error.
If the size of the buffer is between (inclusive) 1217 and 1224 I can trigger the bug.
If the buffer is larger than 1225 I get a message error too big, too.

I'll look at it again tomorrow.

Greetings,

  Hannes

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