From: Shigeru Yoshida <syoshida@redhat.com>

Date: Fri, 25 Nov 2022 02:51:34 +0900

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

Patch-mainline: v6.1-rc8

Git-commit: 5daadc86f27ea4d691e2131c04310d0418c6cd12

References: git-fixes

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>

Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>

---

 drivers/net/tun.c |    4 +++-

 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c

+++ b/drivers/net/tun.c

@@ -678,7 +678,6 @@ static void __tun_detach(struct tun_file

 		if (tun)

 			xdp_rxq_info_unreg(&tfile->xdp_rxq);

 		ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);

-		sock_put(&tfile->sk);

 	}

 }

@@ -694,6 +693,9 @@ static void tun_detach(struct tun_file *

 	if (dev)

 		netdev_state_change(dev);

 	rtnl_unlock();

+

+	if (clean)

+		sock_put(&tfile->sk);

 }

 static void tun_detach_all(struct net_device *dev)