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The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)
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Johannes Berg ea6b2098dd cfg80211: fix locking in netlink owner interface destruction 
Harald Arnesen reported [1] a deadlock at reboot time, and after
he captured a stack trace a picture developed of what's going on:

The distribution he's using is using iwd (not wpa_supplicant) to
manage wireless. iwd will usually use the "socket owner" option
when it creates new interfaces, so that they're automatically
destroyed when it quits (unexpectedly or otherwise). This is also
done by wpa_supplicant, but it doesn't do it for the normal one,
only for additional ones, which is different with iwd.

Anyway, during shutdown, iwd quits while the netdev is still UP,
i.e. IFF_UP is set. This causes the stack trace that Linus so
nicely transcribed from the pictures:

cfg80211_destroy_iface_wk() takes wiphy_lock
 -> cfg80211_destroy_ifaces()
  ->ieee80211_del_iface
    ->ieeee80211_if_remove
      ->cfg80211_unregister_wdev
        ->unregister_netdevice_queue
          ->dev_close_many
            ->__dev_close_many
              ->raw_notifier_call_chain
                ->cfg80211_netdev_notifier_call
and that last call tries to take wiphy_lock again.

In commit a05829a722 ("cfg80211: avoid holding the RTNL when
calling the driver") I had taken into account the possibility of
recursing from cfg80211 into cfg80211_netdev_notifier_call() via
the network stack, but only for NETDEV_UNREGISTER, not for what
happens here, NETDEV_GOING_DOWN and NETDEV_DOWN notifications.

Additionally, while this worked still back in commit 78f22b6a3a
("cfg80211: allow userspace to take ownership of interfaces"), it
missed another corner case: unregistering a netdev will cause
dev_close() to be called, and thus stop wireless operations (e.g.
disconnecting), but there are some types of virtual interfaces in
wifi that don't have a netdev - for that we need an additional
call to cfg80211_leave().

So, to fix this mess, change cfg80211_destroy_ifaces() to not
require the wiphy_lock(), but instead make it acquire it, but
only after it has actually closed all the netdevs on the list,
and then call cfg80211_leave() as well before removing them
from the driver, to fix the second issue. The locking change in
this requires modifying the nl80211 call to not get the wiphy
lock passed in, but acquire it by itself after flushing any
potentially pending destruction requests.

[1] https://lore.kernel.org/r/09464e67-f3de-ac09-28a3-e27b7914ee7d@skogtun.org

Cc: stable@vger.kernel.org # 5.12
Reported-by: Harald Arnesen <harald@skogtun.org>
Fixes: 776a39b819 ("cfg80211: call cfg80211_destroy_ifaces() with wiphy lock held")
Fixes: 78f22b6a3a ("cfg80211: allow userspace to take ownership of interfaces")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Harald Arnesen <harald@skogtun.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2021-04-27 08:30:49 -07:00
Documentation spi: Updates for v5.13 2021-04-26 16:32:11 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
arch spi: Updates for v5.13 2021-04-26 16:32:11 -07:00
block block: return -EBUSY when there are open partitions in blkdev_reread_part 2021-04-21 10:49:37 -06:00
certs certs: add 'x509_revocation_list' to gitignore 2021-04-26 10:48:07 -07:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-04-26 08:51:23 -07:00
drivers spi: Updates for v5.13 2021-04-26 16:32:11 -07:00
fs for-5.13-tag 2021-04-26 13:48:02 -07:00
include spi: Updates for v5.13 2021-04-26 16:32:11 -07:00
init stack: Optionally randomize kernel stack offset each syscall 2021-04-08 14:05:19 +02:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel Power management updates for 5.13-rc1 2021-04-26 15:10:25 -07:00
lib ARM: platform support for Apple M1 2021-04-26 12:30:36 -07:00
mm arm64 updates for 5.13: 2021-04-26 10:25:03 -07:00
net cfg80211: fix locking in netlink owner interface destruction 2021-04-27 08:30:49 -07:00
samples Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
scripts It's been a relatively busy cycle in docsland, though more than usually 2021-04-26 13:22:43 -07:00
security Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-04-26 08:51:23 -07:00
sound TTY/Serial driver updates for 5.13-rc1 2021-04-26 11:20:10 -07:00
tools spi: Updates for v5.13 2021-04-26 16:32:11 -07:00
usr Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
virt KVM: x86/mmu: Consider the hva in mmu_notifier retry 2021-02-22 13:16:53 -05:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap It's been a relatively busy cycle in docsland, though more than usually 2021-04-26 13:22:43 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS It's been a relatively busy cycle in docsland, though more than usually 2021-04-26 13:22:43 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS spi: Updates for v5.13 2021-04-26 16:32:11 -07:00
Makefile Entry code update: 2021-04-26 10:02:09 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.