From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Thu,  4 Apr 2013 15:50:54 -0400
To: 9fans@9fans.net
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Subject: [9fans] IOHDRSZ
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i wonder if  the typical use of IOHDRSZ is correct.

many programs set
	msize = bufsize + IOHDRSIZE
but Twrite has 2+4+8+4=18 bytes overhead, so
i think this assumption is going to lead to
6-byte buffer overruns.

- erik



From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Thu,  4 Apr 2013 21:14:08 +0100
Message-ID: <CAOw7k5hNYLF-B=MnGaKejUM97E2Q5MASANP2EnEJzpi-yyPvMQ@mail.gmail.com>
From: Charles Forsyth <charles.forsyth@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] IOHDRSZ
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On 4 April 2013 20:50, erik quanstrom <quanstro@quanstro.net> wrote:

> so
> i think this assumption is going to lead to
> 6-byte buffer overruns.
>

I don't follow the reasoning. bufsize + Rread or Twrite will always fit.
bufsize is the limit for application data. The receiving 9P also trims the
count
to match the receiving buffer.

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<div dir=3D"ltr"><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">=
On 4 April 2013 20:50, erik quanstrom <span dir=3D"ltr">&lt;<a href=3D"mail=
to:quanstro@quanstro.net" target=3D"_blank">quanstro@quanstro.net</a>&gt;</=
span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div id=3D":4we">so<br>
i think this assumption is going to lead to<br>
6-byte buffer overruns.</div></blockquote></div><div class=3D"gmail_extra">=
<br></div>I don&#39;t follow the reasoning. bufsize + Rread or Twrite will =
always fit.</div><div class=3D"gmail_extra" style>bufsize is the limit for =
application data. The receiving 9P also trims the count</div>
<div class=3D"gmail_extra" style>to match the receiving buffer.<br><br></di=
v></div>

--089e010d8574f7adb104d98e9c84--



From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Thu,  4 Apr 2013 16:49:08 -0400
To: 9fans@9fans.net
Message-ID: <0b2786f721d464915432e88eed91c18f@ladd.quanstro.net>
In-Reply-To: <CAOw7k5hNYLF-B=MnGaKejUM97E2Q5MASANP2EnEJzpi-yyPvMQ@mail.gmail.com>
References: <1d60ad5fac2f22abe5687a2325ab9c63@ladd.quanstro.net>
	<CAOw7k5hNYLF-B=MnGaKejUM97E2Q5MASANP2EnEJzpi-yyPvMQ@mail.gmail.com>
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Subject: Re: [9fans] IOHDRSZ
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> On 4 April 2013 20:50, erik quanstrom <quanstro@quanstro.net> wrote:
>
> > so
> > i think this assumption is going to lead to
> > 6-byte buffer overruns.
> >
>
> I don't follow the reasoning. bufsize + Rread or Twrite will always fit.
> bufsize is the limit for application data. The receiving 9P also trims the
> count
> to match the receiving buffer.

i'm thinking of applications that have a seperate buffer for data.
in this case, i can't think of a clean way of sizing that seperate buffer
correctly.  if msize=bufsize+IOHDRSZ, then incoming bytes would
be too big.

- erik