Messages in this thread | | | Date | Wed, 23 Nov 2022 03:10:05 +0900 (JST) | Subject | Re: [PATCH v2] net: tun: Fix use-after-free in tun_detach() | From | Shigeru Yoshida <> |
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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...).
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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