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

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> From: "Alexey Dobriyan" <adobriyan@gmail.com>
> To: akpm@linux-foundation.org
> Cc: linux-kernel@vger.kernel.org, gorcunov@openvz.org, jarod@redhat.com, jstancek@redhat.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@gmail.com>
> Tested-by: Jarod Wilson <jarod@redhat.com>
> Acked-by: Jarod Wilson <jarod@redhat.com>
> ---
> 
> 	v5: fix BUG_ON(env_start > env_end)

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

Regards,
Jan