linux-kernel - Re: [PATCH 2/2] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline

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Date:	Thu, 28 May 2015 07:57:11 -0400 (EDT)
From:	Jan Stancek <jstancek@...hat.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	gorcunov@...nvz.org, jarod@...hat.com
Subject: Re: [PATCH 2/2] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline





----- Original Message -----
> From: "Alexey Dobriyan" <adobriyan@...il.com>
> To: akpm@...ux-foundation.org
> Cc: linux-kernel@...r.kernel.org, gorcunov@...nvz.org, jarod@...hat.com, jstancek@...hat.com
> Sent: Wednesday, 27 May, 2015 11:49:53 PM
> Subject: [PATCH 2/2] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline
> 
> /proc/$PID/cmdline truncates output at PAGE_SIZE. It is easy to see with
> 
> 	$ cat /proc/self/cmdline $(seq 1037) 2>/dev/null
> 
> However, command line size was never limited to PAGE_SIZE but to 128 KB and
> relatively recently limitation was removed altogether.
> 
> People noticed and ask questions:
> http://stackoverflow.com/questions/199130/how-do-i-increase-the-proc-pid-cmdline-4096-byte-limit
> 
> seq file interface is not OK, because it kmalloc's for whole output and
> open + read(, 1) + sleep will pin arbitrary amounts of kernel memory.
> To not do that, limit must be imposed which is incompatible with
> arbitrary sized command lines.
> 
> I apologize for hairy code, but this it direct consequence of command line
> layout in memory and hacks to support things like "init [3]".
> 
> The loops are "unrolled" otherwise it is either macros which hide
> control flow or functions with 7-8 arguments with equal line count.
> 
> There should be real setproctitle(2) or something.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> Tested-by: Jarod Wilson <jarod@...hat.com>
> Acked-by: Jarod Wilson <jarod@...hat.com>
> ---
> 
> 	v5: fix BUG_ON(env_start > env_end)

I can no longer trigger this BUG_ON() with v5 of the patch.

Regards,
Jan
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