Re: [TLS] PR#625: Change alert requirements

David Benjamin <davidben@chromium.org> Wed, 07 September 2016 18:46 UTC

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From: David Benjamin <davidben@chromium.org>
Date: Wed, 07 Sep 2016 18:46:25 +0000
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To: Eric Rescorla <ekr@rtfm.com>, Andrei Popov <Andrei.Popov@microsoft.com>
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Subject: Re: [TLS] PR#625: Change alert requirements
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On Wed, Sep 7, 2016 at 2:21 PM Eric Rescorla <ekr@rtfm.com>; wrote:

> On Wed, Sep 7, 2016 at 11:19 AM, Andrei Popov <Andrei.Popov@microsoft.com>;
> wrote:
>
> > > the only popular stack I found that does not seem to send alerts is
> > > the schannel from Microsoft
>
> To clarify, schannel does generate alerts per RFC, but the HTTP stack
> (which actually owns the socket) sees no value in sending them.
>
>
> My impression is that this sometimes applies to Chrome as well.
>

Chrome doesn't send close_notify. I'm not sure if error alerts get
swallowed or not. I thought they did, but they do seem to make it through
some layers in the stack. Probably whether they manage to get sent depends
on how long higher layers happen to hold on to objects when an error is
reported.

For Chrome, writing to a socket is asynchronous (we have some
callback-based interface which ultimately uses select/poll/whatever +
non-blocking write/send on POSIX), but tearing down a socket or its owners
is synchronous (it's just C++ delete), so we would attempt to post the
write but then immediately cancel everything if it's just before everything
gets torn down. Trying to wait for that write to actually clear (and then
account for timing it out if it takes forever, etc) would be a ton of
trouble and not actually do much useful. I imagine Andrei's story with the
HTTP stack is similar.

David