Re: [RFC c/r 3/4] c/r: procfs: add arg_start/end, env_start/end and exit_code members to /proc/$pid/stat

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

On 1/27/2012 12:53 PM, Cyrill Gorcunov wrote:
> We would like to have an ability to restore command line
> arguments and envirion pointers so the task being restored
> would print appropriate values in /proc/pid/cmdline and
> /proc/pid/envirion. The exit_code is needed to restore
> zombie tasks.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> Cc: Pavel Emelyanov <xemul@parallels.com>
> Cc: Serge Hallyn <serge.hallyn@canonical.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Andrew Vagin <avagin@openvz.org>
> Cc: Vasiliy Kulikov <segoon@openwall.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>  Documentation/filesystems/proc.txt |    5 +++++
>  fs/proc/array.c                    |   23 ++++++++++++++++++-----
>  2 files changed, 23 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6.git/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux-2.6.git.orig/Documentation/filesystems/proc.txt
> +++ linux-2.6.git/Documentation/filesystems/proc.txt
> @@ -311,6 +311,11 @@ Table 1-4: Contents of the stat files (a
>    start_data    address above which program data+bss is placed
>    end_data      address below which program data+bss is placed
>    start_brk     address above which program heap can be expanded with brk()
> +  arg_start     address above which program command line is placed
> +  arg_end       address below which program command line is placed
> +  env_start     address above which program environment is placed
> +  env_end       address below which program environment is placed
> +  exit_code     the thread's exit_code in the form reported by the waitpid system call
>  ..............................................................................
>  
>  The /proc/PID/maps file containing the currently mapped memory regions and
> Index: linux-2.6.git/fs/proc/array.c
> ===================================================================
> --- linux-2.6.git.orig/fs/proc/array.c
> +++ linux-2.6.git/fs/proc/array.c
> @@ -464,7 +464,7 @@ static int do_task_stat(struct seq_file
>  
>  	seq_printf(m, "%d (%s) %c %d %d %d %d %d %u %lu \
>  %lu %lu %lu %lu %lu %ld %ld %ld %ld %d 0 %llu %lu %ld %lu %lu %lu %lu %lu \
> -%lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu %lu %ld %lu %lu %lu\n",
> +%lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu %lu %ld ",
>  		pid_nr_ns(pid, ns),
>  		tcomm,
>  		state,
> @@ -511,10 +511,23 @@ static int do_task_stat(struct seq_file
>  		task->policy,
>  		(unsigned long long)delayacct_blkio_ticks(task),
>  		cputime_to_clock_t(gtime),
> -		cputime_to_clock_t(cgtime),
> -		(mm && permitted) ? mm->start_data : 0,
> -		(mm && permitted) ? mm->end_data : 0,
> -		(mm && permitted) ? mm->start_brk : 0);
> +		cputime_to_clock_t(cgtime));
> +
> +		if (mm && permitted) {
> +			seq_printf(m, "%lu %lu %lu %lu %lu %lu %lu ",
> +				   mm->start_data,
> +				   mm->end_data,
> +				   mm->start_brk,
> +				   mm->arg_start,
> +				   mm->arg_end,
> +				   mm->env_start,
> +				   mm->env_end);
> +		} else {
> +			seq_printf(m, "0 0 0 0 0 0 0 ");
> +		}

This part seems good.


> +
> +		seq_printf(m, "%d\n", task->exit_code);
> +

Bad this part seems to make new side channel. exit_code is one of inter process communication messages.
IPC messages should NOT be observed from completely unrelated proesses.