linux-kernel - Re: [PATCH net] udp: Fix __ip_append_data()'s handling of MSG_SPLICE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <64c975155d6f3_1d4d6f2941e@willemb.c.googlers.com.notmuch>
Date:   Tue, 01 Aug 2023 17:11:49 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     David Howells <dhowells@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     dhowells@...hat.com, netdev@...r.kernel.org,
        syzbot+f527b971b4bdc8e79f9e@...kaller.appspotmail.com,
        bpf@...r.kernel.org, brauner@...nel.org, davem@...emloft.net,
        dsahern@...nel.org, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, axboe@...nel.dk, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] udp: Fix __ip_append_data()'s handling of
 MSG_SPLICE_PAGES

David Howells wrote:
> Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:
> 
> > __ip6_append_data probably needs the same.
> 
> Now that's interesting.  __ip6_append_data() has a check for this and returns
> -EINVAL in this case:
> 
> 		copy = datalen - transhdrlen - fraggap - pagedlen;
> 		if (copy < 0) {
> 			err = -EINVAL;
> 			goto error;
> 		}
> 
> but should I bypass that check for MSG_SPLICE_PAGES?  It hits the check when
> it should be able to get past it.  The code seems to go back to prehistoric
> times, so I'm not sure why it's there.

Argh, saved by inconsistency between the two stacks.

I don't immediately understand the race that caused this code to move,
in commit 232cd35d0804 ("ipv6: fix out of bound writes in __ip6_append_data()").
Maybe a race with a mtu update?

Technically there is no Fixes tag to apply, so this would not be a fix
for net.

If we want equivalent behavior, a patch removing this branch is probably
best sent to net-next, in a way that works from the start.