Messages in this thread | | | From | Eric Dumazet <> | Date | Tue, 22 Nov 2022 10:47:01 -0800 | Subject | Re: [PATCH v2] net: tun: Fix use-after-free in tun_detach() |
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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 ?
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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