[PATCH] sched: debug: use task_pid_vnr in /proc/$pid/sched

[PATCH] sched: debug: use task_pid_vnr in /proc/$pid/sched

[Aleksa Sarai]

It appears as though the addition of the PID namespace did not update
the output code for /proc/$pid/sched, which made it trivial to figure
out whether a process was inside &init_pid_ns from userspace (making
container detection trivial[1]). This lead to situations such as:

  % unshare -pf head -n1 /proc/self/sched
  head (10047, #threads: 1)

Fix this by just using task_pid_vnr for the output of /proc/$pid/sched.
All of the other uses of task_pid_nr in kernel/sched/debug.c are from a
sysctl context and thus don't need to be namespaced.

[1]: https://github.com/jessfraz/amicontained

Cc: <stable@vger.kernel.org>
Cc: Jess Frazelle <acidburn@google.com>
Signed-off-by: Aleksa Sarai <asarai@suse.com>
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 4fa66de52bd6..a06acbe33e16 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -876,7 +876,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
 {
 	unsigned long nr_switches;
 
-	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_nr(p),
+	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_vnr(p),
 						get_nr_threads(p));
 	SEQ_printf(m,
 		"---------------------------------------------------------"
-- 
2.13.3

Re: [PATCH] sched: debug: use task_pid_vnr in /proc/$pid/sched

[Aleksa Sarai]

On 2017-08-06 02:52, Aleksa Sarai wrote:
> It appears as though the addition of the PID namespace did not update
> the output code for /proc/$pid/sched, which made it trivial to figure
> out whether a process was inside &init_pid_ns from userspace (making
> container detection trivial[1]). This lead to situations such as:
> 
>   % unshare -pf head -n1 /proc/self/sched
>   head (10047, #threads: 1)
> 
> Fix this by just using task_pid_vnr for the output of /proc/$pid/sched.
> All of the other uses of task_pid_nr in kernel/sched/debug.c are from a
> sysctl context and thus don't need to be namespaced.
> 
> [1]: https://github.com/jessfraz/amicontained
> 
> Cc: <stable@vger.kernel.org>
> Cc: Jess Frazelle <acidburn@google.com>
> Signed-off-by: Aleksa Sarai <asarai@suse.com>
> ---
>  kernel/sched/debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 4fa66de52bd6..a06acbe33e16 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -876,7 +876,7 @@ void proc_sched_show_task(struct task_struct *p,
> struct seq_file *m)
>  {
>  	unsigned long nr_switches;
> 
> -	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_nr(p),
> +	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_vnr(p),
>  						get_nr_threads(p));
>  	SEQ_printf(m,
>  		"---------------------------------------------------------"

Added Eric to Cc.

-- 
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/

Re: [PATCH] sched: debug: use task_pid_vnr in /proc/$pid/sched

[Eric W. Biederman]

Aleksa Sarai <asarai@suse.de> writes:

> On 2017-08-06 02:52, Aleksa Sarai wrote:
>> It appears as though the addition of the PID namespace did not update
>> the output code for /proc/$pid/sched, which made it trivial to figure
>> out whether a process was inside &init_pid_ns from userspace (making
>> container detection trivial[1]). This lead to situations such as:
>>
>>   % unshare -pf head -n1 /proc/self/sched
>>   head (10047, #threads: 1)
>>
>> Fix this by just using task_pid_vnr for the output of /proc/$pid/sched.
>> All of the other uses of task_pid_nr in kernel/sched/debug.c are from a
>> sysctl context and thus don't need to be namespaced.
>>
>> [1]: https://github.com/jessfraz/amicontained


>>
>> Cc: <stable@vger.kernel.org>
>> Cc: Jess Frazelle <acidburn@google.com>
>> Signed-off-by: Aleksa Sarai <asarai@suse.com>
>> ---
>>  kernel/sched/debug.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
>> index 4fa66de52bd6..a06acbe33e16 100644
>> --- a/kernel/sched/debug.c
>> +++ b/kernel/sched/debug.c
>> @@ -876,7 +876,7 @@ void proc_sched_show_task(struct task_struct *p,
>> struct seq_file *m)
>>  {
>>  	unsigned long nr_switches;
>>
>> -	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_nr(p),
>> +	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_vnr(p),
>>  						get_nr_threads(p));
>>  	SEQ_printf(m,
>>  		"---------------------------------------------------------"
>
> Added Eric to Cc.

Changing this to pid_nr_ns, to make this relative to the pid namespace
of proc would be very reasonable.

Making files content relative to current is in general a bug.

Hiding the fact you are contained is not an explicit goal.  But making
those things that are reasonably in a namespace relative to that
namespace is.

Eric