linux-kernel - [PATCH v1 0/3] posix-cpu-timers: Use pids not tasks in lookup

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Message-ID: <87h7x142an.fsf_-_@x220.int.ebiederm.org>
Date:   Thu, 30 Apr 2020 06:54:08 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v1 0/3] posix-cpu-timers: Use pids not tasks in lookup

The current posix-cpu-timer code uses pids when holding persistent
references in timers.  However the lookups from clockid_t still return
tasks that need to be converted into pids for use.

This results in usage being pid->task->pid and that can race with
release_task and de_thread.  This can lead to some not wrong but
surprising results.  Surprising enough that Oleg and I both thought
there were some bugs in the code for a while.

This set of changes modifies the code to just lookup, verify, and return
pids from the clockid_t lookups to remove those potentialy troublesome
races.

Eric W. Biederman (3):
      posix-cpu-timers: Extend rcu_read_lock removing task_struct references
      posix-cpu-timers: Replace cpu_timer_pid_type with clock_pid_type
      posix-cpu-timers: Replace __get_task_for_clock with pid_for_clock

 kernel/time/posix-cpu-timers.c | 102 ++++++++++++++++++-----------------------
 1 file changed, 45 insertions(+), 57 deletions(-)

Suggested-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

---

The changes can also be found here:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git proc-testing