Messages in this thread | | | Date | Thu, 24 Nov 2022 01:08:31 +0900 (JST) | Subject | Re: [PATCH v2] net: tun: Fix use-after-free in tun_detach() | From | Shigeru Yoshida <> |
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Hi Jason,
On Wed, 23 Nov 2022 12:20:47 +0800, Jason Wang wrote: > > 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.
Thank you so much for your comment. I'll prepare v3 patch to remove calling synchronize_rcu().
Thanks, Shigeru
> 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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