From: Denton Liu <liu.denton@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Git Mailing List <git@vger.kernel.org>,
Eric Sunshine <sunshine@sunshineco.com>
Subject: Re: [PATCH v2 0/7] remote-curl: fix deadlocks when remote server disconnects
Date: Mon, 18 May 2020 13:36:52 -0400 [thread overview]
Message-ID: <20200518173652.GB2462058@generichostname> (raw)
In-Reply-To: <20200518165056.GD42240@coredump.intra.peff.net>
Hi Peff,
On Mon, May 18, 2020 at 12:50:56PM -0400, Jeff King wrote:
> On Mon, May 18, 2020 at 11:47:17AM -0400, Denton Liu wrote:
>
> > Changes since v1:
> >
> > * Remove fallthrough in switch in favour of just extracting the common
> > call out of the switch in patch 3
> >
> > * Add more detail in function comment and use `const char linelen[4]` in
> > patch 4
> >
> > * Implement most of Peff's suggestions[0] in patch 5
> >
> > * Only operate on stateless_connect() in patch 5
> >
> > * Add tests in patch 5
> >
> > * Drop "remote-curl: ensure last packet is a flush" in favour of
> > "stateless-connect: send response end packet"
>
> Overall this looks pretty cleanly done. I left a few minor comments
> throughout, but the real question is whether we prefer the "0002" packet
> in the last one, or if we instead insist that the response end in a
> flush.
Thanks for the prompt review!
> At first glance, the "0002" seems like it's more flexible, because we're
> making fewer assumptions about what's being transferred over the
> stateless-connect channel. But in reality it still has to be pktlines
> (because we're checking them for incomplete or invalid packets already).
> So all it really buys us is that the server response doesn't have to end
> with a flush packet.
>
> So I dunno. The "0002" solution is slightly more flexible, but I'm not
> sure it helps in practice. And it does eat up one of our two remaining
> special packet markers.
Yeah, I was worried about consuming a special packet. One alternative
that I considered but is kind of gross is sending something like
"0028gitremote-helper: response complete\n" instead of "0002". Then,
instead of "0002" checks, we can check for that special string instead.
I don't _think_ that stateless-connect currently allows for completely
arbitrary data but I might be mistaken.
> There is another solution, which would allow arbitrary data over
> stateless-connect: adding an extra level of pktline framing between the
> helper and the parent process. But that's rather ugly (inner pktlines
> may be split across outer ones, so you have to do a bunch of buffer
> reassembly). I think that's actually how v0 http works, IIRC.
> IMHO it probably isn't worth pursuing. That extra layer wrecks the
> elegance to the v2 stateless-connect approach, and we really do expect
> only pktlines to go over it.
This was the original approach that I was working on but I found it to
be much too invasive for my liking. (Also, I never actually managed to
get it working ;) ) I think I gave up when I realised I had to insert
reframing logic into index-pack and unpack-objects.
> So I think either of your solutions (enforcing a final flush, or the
> 0002 packet) is preferable. I'm on the fence between them.
I'm mostly on the fence too. One advantage of 0002, however, is that a
malicious server can't end a request with 0002 as that's explicitly
prevented. If a malicious server closes a connection after sending a
0000, I think that they could cause a deadlock to happen if there are
multiple flush packets expected in a response. You mentioned in a
sibling email that this currently doesn't happen wrt stateless-connect
although I'm not sure if in the future, this is something that might
change. I dunno.
> -Peff
next prev parent reply other threads:[~2020-05-18 17:36 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 18:04 [PATCH 0/6] remote-curl: partial fix for a deadlock with stateless rpc Denton Liu
2020-05-13 18:04 ` [PATCH 1/6] remote-curl: fix typo Denton Liu
2020-05-13 18:04 ` [PATCH 2/6] remote-curl: remove label indentation Denton Liu
2020-05-13 18:04 ` [PATCH 3/6] transport: combine common cases with a fallthrough Denton Liu
2020-05-13 23:14 ` Eric Sunshine
2020-05-18 9:18 ` Denton Liu
2020-05-18 17:43 ` Eric Sunshine
2020-05-13 18:04 ` [PATCH 4/6] pkt-line: extern packet_length() Denton Liu
2020-05-13 23:23 ` Eric Sunshine
2020-05-15 20:56 ` Jeff King
2020-05-15 20:57 ` Jeff King
2020-05-13 18:04 ` [PATCH 5/6] remote-curl: error on incomplete packet Denton Liu
2020-05-15 21:38 ` Jeff King
2020-05-18 9:08 ` Denton Liu
2020-05-18 15:49 ` Jeff King
2020-05-13 18:04 ` [PATCH 6/6] remote-curl: ensure last packet is a flush Denton Liu
2020-05-15 21:02 ` Denton Liu
2020-05-15 21:41 ` Jeff King
2020-05-18 16:34 ` Junio C Hamano
2020-05-18 16:52 ` Jeff King
2020-05-18 21:00 ` Jeff King
2020-05-18 15:47 ` [PATCH v2 0/7] remote-curl: fix deadlocks when remote server disconnects Denton Liu
2020-05-18 15:47 ` [PATCH v2 1/7] remote-curl: fix typo Denton Liu
2020-05-18 15:47 ` [PATCH v2 2/7] remote-curl: remove label indentation Denton Liu
2020-05-18 18:37 ` Junio C Hamano
2020-05-18 15:47 ` [PATCH v2 3/7] transport: extract common fetch_pack() call Denton Liu
2020-05-18 18:40 ` Junio C Hamano
2020-05-18 15:47 ` [PATCH v2 4/7] pkt-line: extern packet_length() Denton Liu
2020-05-18 16:04 ` Jeff King
2020-05-18 17:50 ` Eric Sunshine
2020-05-18 20:08 ` Jeff King
2020-05-18 18:44 ` Junio C Hamano
2020-05-18 15:47 ` [PATCH v2 5/7] remote-curl: error on incomplete packet Denton Liu
2020-05-18 16:22 ` Jeff King
2020-05-18 16:51 ` Denton Liu
2020-05-18 15:47 ` [PATCH v2 6/7] pkt-line: PACKET_READ_RESPONSE_END Denton Liu
2020-05-18 15:47 ` [PATCH v2 7/7] stateless-connect: send response end packet Denton Liu
2020-05-18 16:43 ` Jeff King
2020-05-18 17:12 ` Denton Liu
2020-05-18 17:26 ` Jeff King
2020-05-18 16:50 ` [PATCH v2 0/7] remote-curl: fix deadlocks when remote server disconnects Jeff King
2020-05-18 17:36 ` Denton Liu [this message]
2020-05-18 20:58 ` Jeff King
2020-05-18 22:52 ` Junio C Hamano
2020-05-19 2:38 ` Jeff King
2020-05-18 19:36 ` Junio C Hamano
2020-05-19 10:53 ` [PATCH v3 " Denton Liu
2020-05-19 10:53 ` [PATCH v3 1/7] remote-curl: fix typo Denton Liu
2020-05-19 10:53 ` [PATCH v3 2/7] remote-curl: remove label indentation Denton Liu
2020-05-19 10:53 ` [PATCH v3 3/7] transport: extract common fetch_pack() call Denton Liu
2020-05-19 10:53 ` [PATCH v3 4/7] pkt-line: extern packet_length() Denton Liu
2020-05-19 16:23 ` Eric Sunshine
2020-05-19 10:53 ` [PATCH v3 5/7] remote-curl: error on incomplete packet Denton Liu
2020-05-19 10:53 ` [PATCH v3 6/7] pkt-line: define PACKET_READ_RESPONSE_END Denton Liu
2020-05-19 10:54 ` [PATCH v3 7/7] stateless-connect: send response end packet Denton Liu
2020-05-19 18:40 ` [PATCH v3 0/7] remote-curl: fix deadlocks when remote server disconnects Jeff King
2020-05-19 21:14 ` Denton Liu
2020-05-19 20:51 ` [PATCH v3 8/7] fixup! pkt-line: extern packet_length() Denton Liu
2020-05-22 13:33 ` [PATCH v3 9/9] fixup! remote-curl: error on incomplete packet Denton Liu
2020-05-22 15:54 ` Jeff King
2020-05-22 16:05 ` Denton Liu
2020-05-22 16:31 ` Jeff King
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200518173652.GB2462058@generichostname \
--to=liu.denton@gmail.com \
--cc=git@vger.kernel.org \
--cc=peff@peff.net \
--cc=sunshine@sunshineco.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).