linux-kernel - Re: [oss-security] [patch] proc.5: tell how to parse /proc/*/stat correctly

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Message-ID: <20221230201554.xborkqi2x5dvnh6h@jwilk.net>
Date:   Fri, 30 Dec 2022 21:15:54 +0100
From:   Jakub Wilk <jwilk@...lk.net>
To:     <oss-security@...ts.openwall.com>
CC:     <linux-man@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [oss-security] [patch] proc.5: tell how to parse /proc/*/stat
 correctly

* Tavis Ormandy <taviso@...il.com>, 2022-12-28 01:50:
>>>But, really, I just don't see how this can practically be said to be 
>>>parsable...
>>
>>In its current form it never will be.  The solution is to place this 
>>variable-length field last.  Then you can "cut -d ' ' -f 51-" to get 
>>the command+args part (assuming I counted all those fields correctly 
>>...)
>>
>>Of course, this breaks backwards compatability.
>
>I think that cut command doesn't handle newlines,

Indeed.

>There already is 'ps -q $$ -o >comm='

FWIW, "ps ... -o comm=" doesn't just print the raw comm value: it 
replaces non-printable chars with punctuation characters, and it may 
append " <defunct>" if the process is a zombie.

The easiest way to get unmangled comm is to read it from 
/proc/$PID/comm, then strip the trailing newline.

(But I suspect most /proc/*/stat parsers don't care about the comm field 
at all; they just want to skip over it to get their hands on the 
following fields.)

-- 
Jakub Wilk