[PATCH] pidns: fix set/getpriority and ioprio_set/get in PRIO_USER mode

[bsegall at google.com]

ebiederm at xmission.com (Eric W. Biederman) writes:

> Andrew Morton <akpm at linux-foundation.org> writes:
>
>> On Wed, 16 Sep 2015 12:58:04 -0700 bsegall at google.com wrote:
>>
>>> setpriority(PRIO_USER, 0, x) will change the priority of tasks outside
>>> of the current pid namespace. This is in contrast to both the other
>>> modes of setpriority and the example of kill(-1). Fix this. getpriority
>>> and ioprio have the same failure mode, fix them too.
>>
>> (cc Eric)
> (cc Containers)
>
> Interesting.  Strictly speaking the current behavior is not wrong.
> Searching for all threads with a given uid has nothing to do with pids
> so the pid namespace not limiting them is natural.
>
> In practice I don't think anyone cares either way (except people with
> one color or another of security hat on) so this might be a change we
> can actually make.
>
> In general it is probably better not to share uids and gids between
> containers.
>
> Ben do you have a use case where this actually matters?  Or was this a
> case of "That looks wrong..."?
>
> Eric

I believe we generally want this for isolation of a process, without
requiring root initially (and a non-trivial uid_map, not to mention
creating the extra users, requires root). There are probably other holes
in using namespaces like this, but are they intended?

(Cc the relevant team member at google)

>
>>> Signed-off-by: Ben Segall <bsegall at google.com>
>>> Cc: Oleg Nesterov <oleg at redhat.com>
>>> Cc: Al Viro <viro at zeniv.linux.org.uk>
>>> ---
>>>  block/ioprio.c | 6 ++++--
>>>  kernel/sys.c   | 4 ++--
>>>  2 files changed, 6 insertions(+), 4 deletions(-)
>>> 
>>> diff --git a/block/ioprio.c b/block/ioprio.c
>>> index 31666c9..cc7800e 100644
>>> --- a/block/ioprio.c
>>> +++ b/block/ioprio.c
>>> @@ -123,7 +123,8 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
>>>  				break;
>>>  
>>>  			do_each_thread(g, p) {
>>> -				if (!uid_eq(task_uid(p), uid))
>>> +				if (!uid_eq(task_uid(p), uid) ||
>>> +				    !task_pid_vnr(p))
>>>  					continue;
>>>  				ret = set_task_ioprio(p, ioprio);
>>>  				if (ret)
>>> @@ -220,7 +221,8 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
>>>  				break;
>>>  
>>>  			do_each_thread(g, p) {
>>> -				if (!uid_eq(task_uid(p), user->uid))
>>> +				if (!uid_eq(task_uid(p), user->uid) ||
>>> +				    !task_pid_vnr(p))
>>>  					continue;
>>>  				tmpio = get_task_ioprio(p);
>>>  				if (tmpio < 0)
>>> diff --git a/kernel/sys.c b/kernel/sys.c
>>> index fa2f2f6..6af9212 100644
>>> --- a/kernel/sys.c
>>> +++ b/kernel/sys.c
>>> @@ -222,7 +222,7 @@ SYSCALL_DEFINE3(setpriority, int, which, int, who, int, niceval)
>>>  				goto out_unlock;	/* No processes for this user */
>>>  		}
>>>  		do_each_thread(g, p) {
>>> -			if (uid_eq(task_uid(p), uid))
>>> +			if (uid_eq(task_uid(p), uid) && task_pid_vnr(p))
>>>  				error = set_one_prio(p, niceval, error);
>>>  		} while_each_thread(g, p);
>>>  		if (!uid_eq(uid, cred->uid))
>>> @@ -290,7 +290,7 @@ SYSCALL_DEFINE2(getpriority, int, which, int, who)
>>>  				goto out_unlock;	/* No processes for this user */
>>>  		}
>>>  		do_each_thread(g, p) {
>>> -			if (uid_eq(task_uid(p), uid)) {
>>> +			if (uid_eq(task_uid(p), uid) && task_pid_vnr(p)) {
>>>  				niceval = nice_to_rlimit(task_nice(p));
>>>  				if (niceval > retval)
>>>  					retval = niceval;
>>> -- 
>>> 2.6.0.rc0.131.gf624c3d
>>> 
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