linux-kernel - [PATCH 0/3] exec: Transform exec_update_mutex into a rw

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Date:   Thu, 03 Dec 2020 14:09:39 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Vasiliy Kulikov <segoon@...nwall.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Christopher Yeoh <cyeoh@....ibm.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Arnd Bergmann <arnd@...db.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: [PATCH 0/3] exec: Transform exec_update_mutex into a rw_semaphore


Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex.

The simplest and most robust solution appears to be making
exec_update_mutex a read/write lock and having everything execept for
exec take the lock for read.

This set of changes upgrades rwsem so it has the functionality needed
and uses a rw_semaphore to replace the current mutex.

Eric W. Biederman (3):
      rwsem: Implement down_read_killable_nested
      rwsem: Implement down_read_interruptible
      exec: Transform exec_update_mutex into a rw_semaphore

 fs/exec.c                    | 12 ++++++------
 fs/proc/base.c               | 10 +++++-----
 include/linux/rwsem.h        |  3 +++
 include/linux/sched/signal.h | 11 ++++++-----
 init/init_task.c             |  2 +-
 kernel/events/core.c         | 12 ++++++------
 kernel/fork.c                |  6 +++---
 kernel/kcmp.c                | 30 +++++++++++++++---------------
 kernel/locking/rwsem.c       | 40 ++++++++++++++++++++++++++++++++++++++++
 kernel/pid.c                 |  4 ++--
 10 files changed, 87 insertions(+), 43 deletions(-)

[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com

Eric