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 notifiercallchain+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> _dumpstack lib/dumpstack.c:88 [inline] dumpstacklvl+0xd1/0x138 lib/dumpstack.c:106 printaddressdescription mm/kasan/report.c:284 [inline] printreport+0x15e/0x461 mm/kasan/report.c:395 kasanreport+0xbf/0x1f0 mm/kasan/report.c:495 notifiercallchain+0x1ee/0x200 kernel/notifier.c:75 callnetdevicenotifiersinfo+0x86/0x130 net/core/dev.c:1942 callnetdevicenotifiersextack net/core/dev.c:1983 [inline] callnetdevicenotifiers net/core/dev.c:1997 [inline] netdevwaitallrefsany net/core/dev.c:10237 [inline] netdevruntodo+0xbc6/0x1100 net/core/dev.c:10351 tundetach drivers/net/tun.c:704 [inline] tunchrclose+0xe4/0x190 drivers/net/tun.c:3467 _fput+0x27c/0xa90 fs/filetable.c:320 taskworkrun+0x16f/0x270 kernel/taskwork.c:179 exittaskwork include/linux/taskwork.h:38 [inline] doexit+0xb3d/0x2a30 kernel/exit.c:820 dogroupexit+0xd4/0x2a0 kernel/exit.c:950 getsignal+0x21b1/0x2440 kernel/signal.c:2858 archdosignalorrestart+0x86/0x2300 arch/x86/kernel/signal.c:869 exittousermodeloop kernel/entry/common.c:168 [inline] exittousermodeprepare+0x15f/0x250 kernel/entry/common.c:203 _syscallexittousermodework kernel/entry/common.c:285 [inline] syscallexittousermode+0x1d/0x50 kernel/entry/common.c:296 dosyscall64+0x46/0xb0 arch/x86/entry/common.c:86 entrySYSCALL64afterhwframe+0x63/0xcd

The cause of the issue is that sockput() from _tundetach() drops last reference count for struct net, and then notifiercallchain() from netdevstate_change() accesses that struct net.

This patch fixes the issue by calling sockput() from tundetach() after all necessary accesses for the struct net has done.