Messages in this thread | | | Date | Wed, 23 Nov 2022 12:20:47 +0800 | Subject | Re: [PATCH v2] net: tun: Fix use-after-free in tun_detach() | From | Jason Wang <> |
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在 2022/11/23 02:47, Eric Dumazet 写道: > On Tue, Nov 22, 2022 at 10:10 AM Shigeru Yoshida <syoshida@redhat.com> wrote: >> Hi Eric, >> >> On Mon, 21 Nov 2022 08:47:17 -0800, Eric Dumazet wrote: >>> On Sun, Nov 20, 2022 at 1:02 AM Shigeru Yoshida <syoshida@redhat.com> wrote: >>>> 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> >>>> --- >>>> v2: >>>> - Include symbolic stack trace >>>> - Add Fixes and Reported-by tags >>>> v1: https://lore.kernel.org/all/20221119075615.723290-1-syoshida@redhat.com/ >>>> --- >>>> drivers/net/tun.c | 6 +++++- >>>> 1 file changed, 5 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >>>> index 7a3ab3427369..ce9fcf4c8ef4 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 +701,11 @@ static void tun_detach(struct tun_file *tfile, bool clean) >>>> if (dev) >>>> netdev_state_change(dev); >>>> rtnl_unlock(); >>>> + >>>> + if (clean) { >>> Would you mind explaining (a comment would be nice) why this barrier is needed ? >> I thought that tfile is accessed with rcu_lock(), so I put >> synchronize_rcu() here. Please let me know if I misunderstand the >> concept of rcu (I'm losing my confidence...). >> > Addin Jason for comments. > > If an RCU grace period was needed before commit 83c1f36f9880 ("tun: > send netlink notification when the device is modified"), > would we need another patch ?
I think we don't need another synchronization here. __tun_detach() has already done the necessary synchronization when it tries to modify tun->tfiles array and tfile->tun.
Thanks
> > Also sock_flag(sk, SOCK_RCU_FREE) would probably be better than adding > a synchronize_rcu() (if again a grace period is needed) > > > >> Thanks, >> Shigeru >> >>> Thanks. >>> >>>> + synchronize_rcu(); >>>> + sock_put(&tfile->sk); >>>> + } >>>> } >>>> >>>> static void tun_detach_all(struct net_device *dev) >>>> -- >>>> 2.38.1 >>>>
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