[PATCH 6.0 066/124] net: tun: Fix use-after-free in tun_detach()

Greg Kroah-Hartman
2022-12-05T19:26:55Z

From: Shigeru Yoshida <syoshida@redhat.com>

[ Upstream commit 5daadc86f27ea4d691e2131c04310d0418c6cd12 ]

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.

Fixes: 83c1f36f9880 ("tun: send netlink notification when the device is modified")
Reported-by: syzbot+106f9b687cd64ee70cd1@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=96eb7f1ce75ef933697f24eeab928c4a716edefe [1]
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Link: https://lore.kernel.org/r/20221124175134.1589053-1-syoshida@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/tun.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3387074a2bdb..167e6a3784ca 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -686,7 +686,6 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
if (tun)
xdp_rxq_info_unreg(&tfile->xdp_rxq);
ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
- sock_put(&tfile->sk);
}
}

@@ -702,6 +701,9 @@ static void tun_detach(struct tun_file *tfile, bool clean)
if (dev)
netdev_state_change(dev);
rtnl_unlock();
+
+ if (clean)
+ sock_put(&tfile->sk);
}

static void tun_detach_all(struct net_device *dev)
--
2.35.1