From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Jones <davej@codemonkey.org.uk>
Subject: Re: ipv6: handle -EFAULT from skb_copy_bits
Date: Tue, 20 Dec 2016 17:12:14 -0500
Message-ID: <20161220221214.w3zerfiy4wu6apee@codemonkey.org.uk>
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Cc: David Miller <davem@davemloft.net>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>
To: Cong Wang <xiyou.wangcong@gmail.com>
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On Tue, Dec 20, 2016 at 11:31:38AM -0800, Cong Wang wrote:
 > On Tue, Dec 20, 2016 at 10:17 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
 > > On Mon, Dec 19, 2016 at 08:36:23PM -0500, David Miller wrote:
 > >  > From: Dave Jones <davej@codemonkey.org.uk>
 > >  > Date: Mon, 19 Dec 2016 19:40:13 -0500
 > >  >
 > >  > > On Mon, Dec 19, 2016 at 07:31:44PM -0500, Dave Jones wrote:
 > >  > >
 > >  > >  > Unfortunately, this made no difference.  I spent some time today trying
 > >  > >  > to make a better reproducer, but failed. I'll revisit again tomorrow.
 > >  > >  >
 > >  > >  > Maybe I need >1 process/thread to trigger this.  That would explain why
 > >  > >  > I can trigger it with Trinity.
 > >  > >
 > >  > > scratch that last part, I finally just repro'd it with a single process.
 > >  >
 > >  > Thanks for the info, I'll try to think about this some more.
 > >
 > > I threw in some debug printks right before that BUG_ON.
 > > it's always this:
 > >
 > > skb->len=31 skb->data_len=0 offset:30 total_len:9
 > 
 > Clearly we fail because 30 > 31 - 2, seems 'offset' is not correct here,
 > off-by-one?

Ok, I finally made a messy, albeit good enough reproducer.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define LEN 504

int main(int argc, char* argv[])
{
	int fd;
	int zero = 0;
	char buf[LEN];

	memset(buf, 0, LEN);

	fd = socket(AF_INET6, SOCK_RAW, 7);

	setsockopt(fd, SOL_IPV6, IPV6_CHECKSUM, &zero, 4);
	setsockopt(fd, SOL_IPV6, IPV6_DSTOPTS, &buf, LEN);

	sendto(fd, buf, 1, 0, (struct sockaddr *) buf, 110);
}