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Eric W. Biederman 117433236a exec: Transform exec_update_mutex into a rw_semaphore 
[ Upstream commit f7cfd871ae ]

Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex.  The problematic lock ordering found by lockdep
was:

   perf_event_open  (exec_update_mutex -> ovl_i_mutex)
   chown            (ovl_i_mutex       -> sb_writes)
   sendfile         (sb_writes         -> p->lock)
     by reading from a proc file and writing to overlayfs
   proc_pid_syscall (p->lock           -> exec_update_mutex)

While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same.  They are all readers.  The only writer is
exec.

There is no reason for readers to block on each other.  So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.

Cc: Jann Horn <jannh@google.com>
Cc: Vasiliy Kulikov <segoon@openwall.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Christopher Yeoh <cyeoh@au1.ibm.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Fixes: eea9673250 ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2021-01-09 13:44:55 +01:00
..
autogroup.h
…
clock.h
…
coredump.h mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary 2020-10-29 09:57:45 +01:00
cpufreq.h cpufreq: Avoid leaving stale IRQ work items during CPU offline 2019-12-31 16:46:06 +01:00
cputime.h posix-cpu-timers: Move state tracking to struct posix_cputimers 2019-08-28 11:50:42 +02:00
deadline.h cpusets: Rebuild root domain deadline accounting information 2019-07-25 15:55:01 +02:00
debug.h
…
hotplug.h
…
idle.h
…
init.h
…
isolation.h KVM: LAPIC: Inject timer interrupt via posted interrupt 2019-07-20 09:00:40 +02:00
jobctl.h cgroup: cgroup v2 freezer 2019-04-19 11:26:48 -07:00
loadavg.h
…
mm.h sched/core: Fix illegal RCU from offline CPUs 2020-06-22 09:31:01 +02:00
nohz.h timers/nohz: Update NOHZ load in remote tick 2020-03-05 16:43:36 +01:00
numa_balancing.h sched/fair: Don't free p->numa_faults with concurrent readers 2019-07-25 15:37:04 +02:00
prio.h
…
rt.h
…
signal.h exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
smt.h
…
stat.h
…
sysctl.h sched/uclamp: Add system default clamps 2019-06-24 19:23:45 +02:00
task.h tasks, sched/core: With a grace period after finish_task_switch(), remove unnecessary code 2019-09-25 17:42:29 +02:00
task_stack.h
…
topology.h sched/topology: Add partition_sched_domains_locked() 2019-07-25 15:51:57 +02:00
types.h posix-cpu-timers: Provide array based access to expiry cache 2019-08-28 11:50:35 +02:00
user.h keys: Move the user and user-session keyrings to the user_namespace 2019-06-26 21:02:32 +01:00
wake_q.h locking/rwsem: Always release wait_lock before waking up tasks 2019-06-17 12:28:00 +02:00
xacct.h
…