linux-kernel - Re: [PATCH] pidns: fix set/getpriority and ioprio_set/get in PRIO

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Date:	Mon, 21 Sep 2015 12:46:56 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	bsegall@...gle.com, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] pidns: fix set/getpriority and ioprio_set/get in PRIO_USER mode

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Wed, 16 Sep 2015 12:58:04 -0700 bsegall@...gle.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

>> Signed-off-by: Ben Segall <bsegall@...gle.com>
>> Cc: Oleg Nesterov <oleg@...hat.com>
>> Cc: Al Viro <viro@...iv.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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