linux-kernel - Re: Large pastes into readline enabled programs causes breakage from v2.6.31 onwards

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Message-ID: <529E2E92.4010004@list.ru>
Date:	Tue, 03 Dec 2013 23:18:42 +0400
From:	Stas Sergeev <stsp@...t.ru>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Margarita Manterola <margamanterola@...il.com>,
	Maximiliano Curia <maxy@...servers.com.ar>,
	Stas Sergeev <stsp@...rs.sourceforge.net>,
	Pavel Machek <pavel@....cz>,
	Arkadiusz Miskiewicz <a.miskiewicz@...il.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Caylan Van Larson <i@...lan.net>
Subject: Re: Large pastes into readline enabled programs causes breakage from
 v2.6.31 onwards

03.12.2013 21:00, Peter Hurley пишет:
> Any unit test is specifically designed to break the code under test.
> This unit test does in fact break a possible input: note specifically
> that the writer is not changing the termios so has no control over
> the timing of when the input is received.
>
> Also note that the test is a simulation; the patch will break any
> input stream under the following conditions:
> 1. The writer writes an EOF-terminated buffer
> 2. All the input is received _except_ the EOF; this is strictly
>    timing-related and not controllable.
> 3. The reader changes the termios from non-canon -> canon.
>
> At that point the damage is done; the read_flags will indicate
> 2 EOFs and the 2nd EOF will be interpreted as end-of-file because
> it will appear to begin on a new line.
How is this different from the unpatched kernel?
In the unpatched kernel, if you happen on reader side
to enable icanon while n_tty received all but VEOF (is this possible at 
all?),
then the buffer will be flushed, and the remaining VEOF
will get you a nice EOF.
So, in the unpatched kernel you get EOF because the buffer
gets wiped.
On patched kernel you get EOF because of 2 consequitive marks
in read_flags.
This is intentional, for backward compatibility.
What is the problem with that, why do you call it a breakage?
Or am I misreading the scenario you describe?
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