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Eric W. Biederman ab7709b551 exec: Transform exec_update_mutex into a rw_semaphore 
[ Upstream commit f7cfd871ae0c5008d94b6f66834e7845caa93c15 ]

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 13:46:24 +01:00
arch s390: always clear kernel stack backchain before calling functions 2021-01-06 14:56:55 +01:00
block scsi: block: Fix a race in the runtime power management code 2021-01-06 14:56:50 +01:00
certs
crypto crypto: ecdh - avoid unaligned accesses in ecdh_set_secret() 2020-12-30 11:54:10 +01:00
Documentation dt-bindings: rtc: add reset-source property 2021-01-09 13:46:22 +01:00
drivers RDMA/siw,rxe: Make emulated devices virtual in the device tree 2021-01-09 13:46:24 +01:00
fs exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:46:24 +01:00
include exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:46:24 +01:00
init exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:46:24 +01:00
ipc
kernel exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:46:24 +01:00
lib zlib: move EXPORT_SYMBOL() and MODULE_LICENSE() out of dfltcc_syms.c 2021-01-06 14:56:51 +01:00
LICENSES
mm mm: memmap defer init doesn't work as expected 2021-01-06 14:56:50 +01:00
net Bluetooth: Fix attempting to set RPA timeout when unsupported 2021-01-09 13:46:23 +01:00
samples samples/bpf: Fix possible hang in xdpsock with multiple threads 2020-12-30 11:53:49 +01:00
scripts kconfig: fix return value of do_error_if() 2020-12-30 11:54:01 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:54:17 +01:00
sound ALSA: hda/hdmi: Fix incorrect mutex unlock in silent_stream_disable() 2021-01-09 13:46:23 +01:00
tools tools headers UAPI: Sync linux/const.h with the kernel headers 2021-01-06 14:56:51 +01:00
usr
virt kvm: x86/mmu: Support dirty logging for the TDP MMU 2020-10-23 03:42:13 -04:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
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.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild
Kconfig
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-10 15:30:13 -08:00
Makefile Linux 5.10.5 2021-01-06 14:56:56 +01:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.