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From: David Howells <dhowells@redhat.com>
To: Eric Dumazet <edumazet@google.com>
Cc: dhowells@redhat.com,
	syzbot <syzbot+62cbf263225ae13ff153@syzkaller.appspotmail.com>,
	bpf@vger.kernel.org, davem@davemloft.net, dsahern@kernel.org,
	kuba@kernel.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, pabeni@redhat.com,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [net?] WARNING in __ip6_append_data
Date: Fri, 15 Sep 2023 16:32:20 +0100	[thread overview]
Message-ID: <3792062.1694791940@warthog.procyon.org.uk> (raw)
In-Reply-To: <CANn89iLwMhOnrmQTZJ+BqZJSbJZ+Q4W6xRknAAr+uSrk5TX-EQ@mail.gmail.com>

Hi Eric,

> > WARNING: CPU: 1 PID: 5042 at net/ipv6/ip6_output.c:1800 __ip6_append_data.isra.0+0x1be8/0x47f0 net/ipv6/ip6_output.c:1800

That would appear to be this:

			if (WARN_ON_ONCE(copy > msg->msg_iter.count))
				goto error;

However, I have a problem that the repro program errors out at this point
before it gets that far:

	if (cork->length + length > maxnonfragsize - headersize) {
   emsgsize:
		pmtu = max_t(int, mtu - headersize + sizeof(struct ipv6hdr), 0);
		ipv6_local_error(sk, EMSGSIZE, fl6, pmtu);
		return -EMSGSIZE;
	}

Are you able to reproduce the issue?

The values in and around that point are:

	cork->length		0
	length			65540
	maxnonfragsize		65575
	headersize		40
	transhdrlen		4
	mtu			65536
	ip6_sk_ignore_df(sk)	true

with maxnonfragsize coming from 'sizeof(struct ipv6hdr) + IPV6_MAXPLEN'.  Is
that even viable for the size of a packet?

David


  parent reply	other threads:[~2023-09-15 15:33 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-13  6:19 syzbot
2023-09-13  8:41 ` Eric Dumazet
2023-09-15 15:32 ` David Howells [this message]
2023-09-15 16:24 ` David Howells
2023-09-18 10:03 ` David Howells
2023-09-18 13:58   ` Willem de Bruijn
2023-09-18 14:04     ` Eric Dumazet
2023-09-19  8:27       ` Tom Parkin
2023-09-19  9:04         ` Eric Dumazet
2023-09-18 14:46   ` David Howells
2023-09-18 10:11 ` David Howells
2023-09-18 10:33   ` syzbot

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