CVE-2022-49014

In the Linux kernel, the following vulnerability has been resolved:

net: tun: Fix use-after-free in tun_detach()

syzbot reported use-after-free in tun_detach() [1]. This causes call

trace like below:

==================================================================

BUG: KASAN: use-after-free in notifier_call_chain+0x1ee/0x200 kernel/notifier.c:75

Read of size 8 at addr ffff88807324e2a8 by task syz-executor.0/3673

CPU: 0 PID: 3673 Comm: syz-executor.0 Not tainted 6.1.0-rc5-syzkaller-00044-gcc675d22e422 #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:88 [inline]

dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106

print_address_description mm/kasan/report.c:284 [inline]

print_report+0x15e/0x461 mm/kasan/report.c:395

kasan_report+0xbf/0x1f0 mm/kasan/report.c:495

notifier_call_chain+0x1ee/0x200 kernel/notifier.c:75

call_netdevice_notifiers_info+0x86/0x130 net/core/dev.c:1942

call_netdevice_notifiers_extack net/core/dev.c:1983 [inline]

call_netdevice_notifiers net/core/dev.c:1997 [inline]

netdev_wait_allrefs_any net/core/dev.c:10237 [inline]

netdev_run_todo+0xbc6/0x1100 net/core/dev.c:10351

tun_detach drivers/net/tun.c:704 [inline]

tun_chr_close+0xe4/0x190 drivers/net/tun.c:3467

__fput+0x27c/0xa90 fs/file_table.c:320

task_work_run+0x16f/0x270 kernel/task_work.c:179

exit_task_work include/linux/task_work.h:38 [inline]

do_exit+0xb3d/0x2a30 kernel/exit.c:820

do_group_exit+0xd4/0x2a0 kernel/exit.c:950

get_signal+0x21b1/0x2440 kernel/signal.c:2858

arch_do_signal_or_restart+0x86/0x2300 arch/x86/kernel/signal.c:869

exit_to_user_mode_loop kernel/entry/common.c:168 [inline]

exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203

__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]

syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296

do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86

entry_SYSCALL_64_after_hwframe+0x63/0xcd

The cause of the issue is that sock_put() from __tun_detach() drops

last reference count for struct net, and then notifier_call_chain()

from netdev_state_change() accesses that struct net.

This patch fixes the issue by calling sock_put() from tun_detach()

after all necessary accesses for the struct net has done.