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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
..
Kconfig printk: reduce LOG_BUF_SHIFT range for H8300 2020-11-05 11:43:16 +01:00
Makefile Kbuild: Handle PREEMPT_RT for version string and magic 2019-08-14 01:10:42 +09:00
calibrate.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
do_mounts.c vfs: Convert ramfs, shmem, tmpfs, devtmpfs, rootfs to use the new mount API 2019-09-12 21:05:34 -04:00
do_mounts.h fs: add do_mknodat() helper and ksys_mknod() wrapper; remove in-kernel calls to syscall 2018-04-02 20:15:56 +02:00
do_mounts_initrd.c Merge branch 'mount.part1' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-01-05 13:25:58 -08:00
do_mounts_md.c init/: remove ineffective sparse disabling 2018-08-22 10:52:49 -07:00
do_mounts_rd.c init/: remove ineffective sparse disabling 2018-08-22 10:52:49 -07:00
init_task.c exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
initramfs.c initramfs: fix clang build failure 2020-12-30 11:51:30 +01:00
main.c kprobes: tracing/kprobes: Fix to kill kprobes on initmem after boot 2020-10-01 13:18:23 +02:00
noinitramfs.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 167 2019-05-30 11:26:39 -07:00
version.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00