From: Jann Horn <jann@thejh.net>
To: Topi Miettinen <toiwoton@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Alexey Dobriyan <adobriyan@gmail.com>,
John Stultz <john.stultz@linaro.org>,
Janis Danisevskis <jdanis@google.com>,
Calvin Owens <calvinowens@fb.com>, Tejun Heo <tj@kernel.org>,
Michal Hocko <mhocko@suse.com>, Oleg Nesterov <oleg@redhat.com>,
Vladimir Davydov <vdavydov@virtuozzo.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Josh Triplett <josh@joshtriplett.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Aleksa Sarai <cyphar@cyphar.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Ben Segall <bsegall@google.com>,
Mateusz Guzik <mguzik@redhat.com>
Subject: Re: [RFC 11/18] limits: track and present RLIMIT_NPROC actual max
Date: Wed, 15 Jun 2016 01:15:54 +0200 [thread overview]
Message-ID: <20160614231554.GA18261@pc.thejh.net> (raw)
In-Reply-To: <3eb3040e-8f73-60d3-f9bf-0c9eaf9ffce1@gmail.com>
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On Tue, Jun 14, 2016 at 03:40:35PM +0000, Topi Miettinen wrote:
> On 06/13/16 22:27, Jann Horn wrote:
> > On Mon, Jun 13, 2016 at 10:44:18PM +0300, Topi Miettinen wrote:
> >> Track maximum number of processes per user and present it
> >> in /proc/self/limits.
> >>
> >> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
> >> ---
> >> fs/proc/base.c | 4 ++++
> >> include/linux/sched.h | 1 +
> >> kernel/fork.c | 5 +++++
> >> kernel/sys.c | 5 +++++
> >> 4 files changed, 15 insertions(+)
> >>
> >> diff --git a/fs/proc/base.c b/fs/proc/base.c
> >> index 1df4fc8..02576c6 100644
> >> --- a/fs/proc/base.c
> >> +++ b/fs/proc/base.c
> >> @@ -670,6 +670,10 @@ static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
> >> seq_printf(m, "%-20lu\n", psecs);
> >> }
> >> break;
> >> + case RLIMIT_NPROC:
> >> + seq_printf(m, "%-20d\n",
> >> + atomic_read(&task->real_cred->user->max_processes));
> >
> > Don't you have to take an RCU read lock before dereferencing task->real_cred?
>
> In other comments in the series, cmpxchg loop was suggested, would that
> work here?
What would a cmpxchg loop have to do with missing RCU locking?
> > And shouldn't this be done with __task_cred(task) instead of task->real_cred?
>
> How about atomic_read(task_cred_xxx(task, user)->max_processes)?
No. You'd still end up dereferencing max_processes in the user_struct without
any guarantee that it hasn't been freed. I think the code should look this way:
case RLIMIT_NPROC:
rcu_read_lock();
seq_printf(m, "%-20d\n",
atomic_read(&__task_cred(task)->user->max_processes));
rcu_read_unlock();
break;
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next prev parent reply other threads:[~2016-06-14 23:16 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-13 19:44 [RFC 00/18] Present useful limits to user Topi Miettinen
2016-06-13 19:44 ` [RFC 01/18] capabilities: track actually used capabilities Topi Miettinen
2016-06-13 20:32 ` Andy Lutomirski
2016-06-13 20:45 ` Topi Miettinen
2016-06-13 21:12 ` Andy Lutomirski
2016-06-13 21:48 ` Topi Miettinen
2016-06-13 19:44 ` [RFC 02/18] cgroup_pids: track maximum pids Topi Miettinen
2016-06-13 21:12 ` Tejun Heo
2016-06-13 21:29 ` Topi Miettinen
2016-06-13 21:33 ` Tejun Heo
2016-06-13 21:59 ` Topi Miettinen
2016-06-13 22:09 ` Tejun Heo
2016-07-17 20:11 ` Topi Miettinen
2016-07-19 1:09 ` Tejun Heo
2016-07-19 16:59 ` Topi Miettinen
2016-07-19 18:13 ` Tejun Heo
2016-06-13 19:44 ` [RFC 03/18] memcontrol: present maximum used memory also for cgroup-v2 Topi Miettinen
2016-06-14 7:01 ` Michal Hocko
2016-06-14 15:47 ` Topi Miettinen
2016-06-14 16:04 ` Johannes Weiner
2016-06-14 17:15 ` Topi Miettinen
2016-06-16 10:27 ` Michal Hocko
2016-06-13 19:44 ` [RFC 04/18] device_cgroup: track and present accessed devices Topi Miettinen
2016-06-17 15:22 ` Serge E. Hallyn
2016-06-13 19:44 ` [RFC 05/18] limits: track and present RLIMIT_NOFILE actual max Topi Miettinen
2016-06-13 20:40 ` Andy Lutomirski
2016-06-13 21:13 ` Topi Miettinen
2016-06-13 21:16 ` Andy Lutomirski
2016-06-14 15:21 ` Topi Miettinen
2016-06-13 19:44 ` [RFC 06/18] limits: present RLIMIT_CPU and RLIMIT_RTTIMER current status Topi Miettinen
2016-06-14 9:14 ` Alexey Dobriyan
2016-06-13 19:44 ` [RFC 07/18] limits: track RLIMIT_FSIZE actual max Topi Miettinen
2016-06-13 19:44 ` [RFC 08/18] limits: track RLIMIT_DATA " Topi Miettinen
2016-06-13 19:44 ` [RFC 09/18] limits: track RLIMIT_CORE " Topi Miettinen
2016-06-13 19:44 ` [RFC 10/18] limits: track RLIMIT_STACK " Topi Miettinen
2016-06-13 19:44 ` [RFC 11/18] limits: track and present RLIMIT_NPROC " Topi Miettinen
2016-06-13 22:27 ` Jann Horn
2016-06-14 15:40 ` Topi Miettinen
2016-06-14 23:15 ` Jann Horn [this message]
2016-06-13 19:44 ` [RFC 13/18] limits: track RLIMIT_AS " Topi Miettinen
2016-06-13 19:44 ` [RFC 14/18] limits: track RLIMIT_SIGPENDING " Topi Miettinen
2016-06-14 14:50 ` Oleg Nesterov
2016-06-14 15:51 ` Topi Miettinen
2016-06-13 19:44 ` [RFC 15/18] limits: track RLIMIT_MSGQUEUE " Topi Miettinen
2016-06-17 19:52 ` Doug Ledford
2016-06-13 19:44 ` [RFC 16/18] limits: track RLIMIT_NICE " Topi Miettinen
2016-06-13 19:44 ` [RFC 17/18] limits: track RLIMIT_RTPRIO " Topi Miettinen
2016-06-13 19:44 ` [RFC 18/18] proc: present VM_LOCKED memory in /proc/self/maps Topi Miettinen
2016-06-13 20:43 ` Kees Cook
2016-06-13 20:52 ` Topi Miettinen
2016-06-14 19:03 ` [RFC 00/18] Present useful limits to user Konstantin Khlebnikov
2016-06-14 19:46 ` Topi Miettinen
2016-06-15 14:47 ` Austin S. Hemmelgarn
2016-06-18 14:45 ` Konstantin Khlebnikov
2016-06-19 6:38 ` Topi Miettinen
2016-06-20 17:37 ` Austin S. Hemmelgarn
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