netdev - Re: use-after-free in sctp_do

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Message-ID: <20151203184316.GF4164@mrl.redhat.com>
Date:	Thu, 3 Dec 2015 16:43:16 -0200
From:	Marcelo <marcelo.leitner@...il.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Neil Horman <nhorman@...driver.com>,
	linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Maciej Żenczykowski <maze@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: use-after-free in sctp_do_sm

On Thu, Dec 03, 2015 at 01:35:37PM -0500, Vlad Yasevich wrote:
> On 12/03/2015 01:06 PM, Marcelo wrote:
> > 
> > 
> > Em 3 de dezembro de 2015 15:59:10 BRST, Eric Dumazet <eric.dumazet@...il.com> escreveu:
> >> On Thu, 2015-12-03 at 15:43 -0200, Marcelo Ricardo Leitner wrote:
> >>
> >>> Vlad, others,
> >>>
> >>> It's been a long time but this was introduced by commit 914e1c8b6980
> >>> ("sctp: Inherit all socket options from parent correctly."). This is
> >> not
> >>> very consistent with how other protocols work and it will be hard to
> >>> keep tracking a negative mask of flags that we can't copy.
> >>>
> >>> I reviewed the list of options and I'm thinking that only
> >>> SO_BINDTODEVICE is worth copying, leaving the others for the
> >> application
> >>> to re-set, as it is for other protocols. So I'm thinking on simply:
> >>>
> >>> -       newsk->sk_flags = sk->sk_flags;
> >>> +       newsk->sk_flags = sk->sk_flags & SO_BINDTODEVICE;
> >>>
> >>> in the above.
> >>>
> >>> What do you think?
> >>
> >> I think SO_BINDTODEVICE is not a flag ;)
> >>
> >> #define SO_BINDTODEVICE    25
> > 
> > Oops, indeed!
> > Idea persists.
> > Thx!
> > 
> 
> Hmm...  sk_clone_lock() appears to copy the flags as well, so it would
> appear the tcp accept() sockets would also have timestamping set.

Ahh right, through a memcpy. I completely missed that.

And later on it does:
                if (sock_needs_netstamp(sk) &&
                    newsk->sk_flags & SK_FLAGS_TIMESTAMP)
                        net_enable_timestamp();

> I can see how we probably shouldn't being copying sk_flags as there isn't
> much there that need to be set.

I take that back then, we can enable timestamp like the above instead.
I'll test and post a patch soon.

Thanks,
Marcelo

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