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

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 20 Mar 2015 20:51:47 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> /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.
> 
> 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.
>
> ...
>
> fs/proc/base.c |  203 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 194 insertions(+), 9 deletions(-)
>

I'm desperately trying to think of a reason to not merge this patch :(

I haven't seen anyone complain about the PAGE_SIZE limit - can't we
pretend we didn't notice?  Or tell 'em to switch to powerpc so they
get 64k!