| Message ID | 20210719024937.9542-1-bobo.shaobowang@huawei.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] Bluetooth: fix use-after-free error in lock_sock_nested() | expand |
Hi Hillf, On Mon, Jul 19, 2021 at 7:16 PM Hillf Danton <hdanton@sina.com> wrote: > > On Mon, 19 Jul 2021 17:03:53 +0800 Wang ShaoBo wrote: > > > >I have tried this before, this will trigger error "underflow of refcount > >of chan" as following: > > > >[ 118.708179][ T3086] ------------[ cut here ]------------ > >[ 118.710172][ T3086] refcount_t: underflow; use-after-free. > >[ 118.713391][ T3086] WARNING: CPU: 4 PID: 3086 at lib/refcount.c:28 > >refcount_warn_saturate+0x30a/0x3c0 > >[ 118.716774][ T3086] Modules linked in: > >[ 118.718279][ T3086] CPU: 4 PID: 3086 Comm: kworker/4:2 Not tainted > >5.12.0-rc6+ #84 > >[ 118.721005][ T3086] Hardware name: QEMU Standard PC (i440FX + PIIX, > >1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 > >[ 118.722846][ T3086] Workqueue: events l2cap_chan_timeout > >[ 118.723786][ T3086] RIP: 0010:refcount_warn_saturate+0x30a/0x3c0 > >... > >[ 118.737912][ T3086] CR2: 0000000020000040 CR3: 0000000011029000 CR4: > >00000000000006e0 > >[ 118.739187][ T3086] DR0: 0000000000000000 DR1: 0000000000000000 DR2: > >0000000000000000 > >[ 118.740451][ T3086] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: > >0000000000000400 > >[ 118.741720][ T3086] Call Trace: > >[ 118.742262][ T3086] l2cap_sock_close_cb+0x165/0x170 > >[ 118.743124][ T3086] ? l2cap_sock_teardown_cb+0x560/0x560 > > > >Actually, if adding sock_hold(sk) in l2cap_sock_init(), > >l2cap_sock_kill() will continue to excute untill it found > > > >now chan's refcount is 0, this is because sock was not freed in last > >round execution of l2cap_sock_kill(). > > Well double kill cannot be walked around without adding more - add the > destroy callback to make the chan->data recorded sock survive kill. It > will be released when chan is destroyed to cut the race in reguards to > accessing sock by making chan->data stable throughout chan's lifespan. > > > +++ x/net/bluetooth/l2cap_core.c > @@ -485,7 +485,10 @@ static void l2cap_chan_destroy(struct kr > list_del(&chan->global_l); > write_unlock(&chan_list_lock); > > - kfree(chan); > + if (chan->ops && chan->ops->destroy) > + chan->ops->destroy(chan); > + else > + kfree(chan); While Im fine adding a destroy callback the kfree shall be still in l2cap_chan_destroy: if (chan->ops && chan->ops->destroy) /* Destroy chan->data */ chan->ops->destroy(chan->data); kfree(chan); > } > > void l2cap_chan_hold(struct l2cap_chan *c) > +++ x/net/bluetooth/l2cap_sock.c > @@ -1220,11 +1220,13 @@ static void l2cap_sock_kill(struct sock > > BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state)); > > + /* double kill means noop */ > + if (sock_flag(sk, SOCK_DEAD)) > + return; > /* Kill poor orphan */ > > l2cap_chan_put(l2cap_pi(sk)->chan); > sock_set_flag(sk, SOCK_DEAD); > - sock_put(sk); > } > > static int __l2cap_wait_ack(struct sock *sk, struct l2cap_chan *chan) > @@ -1504,6 +1506,14 @@ done: > return err; > } > > +static void l2cap_sock_destroy_cb(struct l2cap_chan *chan) > +{ > + struct sock *sk = chan->data; > + > + sock_put(sk); > + kfree(chan); > +} > + > static void l2cap_sock_close_cb(struct l2cap_chan *chan) > { > struct sock *sk = chan->data; > @@ -1690,6 +1700,7 @@ static const struct l2cap_ops l2cap_chan > .new_connection = l2cap_sock_new_connection_cb, > .recv = l2cap_sock_recv_cb, > .close = l2cap_sock_close_cb, > + .destroy = l2cap_sock_destroy_cb, If you do the changes above you can probably have sock_put directly set as .destroy. > .teardown = l2cap_sock_teardown_cb, > .state_change = l2cap_sock_state_change_cb, > .ready = l2cap_sock_ready_cb,
Hi Hillf, On Mon, Jul 19, 2021 at 11:21 PM Hillf Danton <hdanton@sina.com> wrote: > > On Mon, 19 Jul 2021 21:24:30 -0700 Luiz Augusto von Dentz wrote: > > > >While Im fine adding a destroy callback the kfree shall be still in > >l2cap_chan_destroy: > > Then feel free to send a tiny patchset to linux-bluetooth@vger. What do you mean, we haven't applied your changes yet.
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c index c99d65ef13b1..160c016a5dfb 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -1508,6 +1508,9 @@ static void l2cap_sock_close_cb(struct l2cap_chan *chan) { struct sock *sk = chan->data; + if (!sk) + return; + l2cap_sock_kill(sk); } @@ -1516,6 +1519,9 @@ static void l2cap_sock_teardown_cb(struct l2cap_chan *chan, int err) struct sock *sk = chan->data; struct sock *parent; + if (!sk) + return; + BT_DBG("chan %p state %s", chan, state_to_string(chan->state)); /* This callback can be called both for server (BT_LISTEN) @@ -1707,8 +1713,10 @@ static void l2cap_sock_destruct(struct sock *sk) { BT_DBG("sk %p", sk); - if (l2cap_pi(sk)->chan) + if (l2cap_pi(sk)->chan) { + l2cap_pi(sk)->chan->data = NULL; l2cap_chan_put(l2cap_pi(sk)->chan); + } if (l2cap_pi(sk)->rx_busy_skb) { kfree_skb(l2cap_pi(sk)->rx_busy_skb);
use-after-free error in lock_sock_nested is reported: [ 179.140137][ T3731] ===================================================== [ 179.142675][ T3731] BUG: KMSAN: use-after-free in lock_sock_nested+0x280/0x2c0 [ 179.145494][ T3731] CPU: 4 PID: 3731 Comm: kworker/4:2 Not tainted 5.12.0-rc6+ #54 [ 179.148432][ T3731] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 [ 179.151806][ T3731] Workqueue: events l2cap_chan_timeout [ 179.152730][ T3731] Call Trace: [ 179.153301][ T3731] dump_stack+0x24c/0x2e0 [ 179.154063][ T3731] kmsan_report+0xfb/0x1e0 [ 179.154855][ T3731] __msan_warning+0x5c/0xa0 [ 179.155579][ T3731] lock_sock_nested+0x280/0x2c0 [ 179.156436][ T3731] ? kmsan_get_metadata+0x116/0x180 [ 179.157257][ T3731] l2cap_sock_teardown_cb+0xb8/0x890 [ 179.158154][ T3731] ? __msan_metadata_ptr_for_load_8+0x10/0x20 [ 179.159141][ T3731] ? kmsan_get_metadata+0x116/0x180 [ 179.159994][ T3731] ? kmsan_get_shadow_origin_ptr+0x84/0xb0 [ 179.160959][ T3731] ? l2cap_sock_recv_cb+0x420/0x420 [ 179.161834][ T3731] l2cap_chan_del+0x3e1/0x1d50 [ 179.162608][ T3731] ? kmsan_get_metadata+0x116/0x180 [ 179.163435][ T3731] ? kmsan_get_shadow_origin_ptr+0x84/0xb0 [ 179.164406][ T3731] l2cap_chan_close+0xeea/0x1050 [ 179.165189][ T3731] ? kmsan_internal_unpoison_shadow+0x42/0x70 [ 179.166180][ T3731] l2cap_chan_timeout+0x1da/0x590 [ 179.167066][ T3731] ? __msan_metadata_ptr_for_load_8+0x10/0x20 [ 179.168023][ T3731] ? l2cap_chan_create+0x560/0x560 [ 179.168818][ T3731] process_one_work+0x121d/0x1ff0 [ 179.169598][ T3731] worker_thread+0x121b/0x2370 [ 179.170346][ T3731] kthread+0x4ef/0x610 [ 179.171010][ T3731] ? process_one_work+0x1ff0/0x1ff0 [ 179.171828][ T3731] ? kthread_blkcg+0x110/0x110 [ 179.172587][ T3731] ret_from_fork+0x1f/0x30 [ 179.173348][ T3731] [ 179.173752][ T3731] Uninit was created at: [ 179.174409][ T3731] kmsan_internal_poison_shadow+0x5c/0xf0 [ 179.175373][ T3731] kmsan_slab_free+0x76/0xc0 [ 179.176060][ T3731] kfree+0x3a5/0x1180 [ 179.176664][ T3731] __sk_destruct+0x8af/0xb80 [ 179.177375][ T3731] __sk_free+0x812/0x8c0 [ 179.178032][ T3731] sk_free+0x97/0x130 [ 179.178686][ T3731] l2cap_sock_release+0x3d5/0x4d0 [ 179.179457][ T3731] sock_close+0x150/0x450 [ 179.180117][ T3731] __fput+0x6bd/0xf00 [ 179.180787][ T3731] ____fput+0x37/0x40 [ 179.181481][ T3731] task_work_run+0x140/0x280 [ 179.182219][ T3731] do_exit+0xe51/0x3e60 [ 179.182930][ T3731] do_group_exit+0x20e/0x450 [ 179.183656][ T3731] get_signal+0x2dfb/0x38f0 [ 179.184344][ T3731] arch_do_signal_or_restart+0xaa/0xe10 [ 179.185266][ T3731] exit_to_user_mode_prepare+0x2d2/0x560 [ 179.186136][ T3731] syscall_exit_to_user_mode+0x35/0x60 [ 179.186984][ T3731] do_syscall_64+0xc5/0x140 [ 179.187681][ T3731] entry_SYSCALL_64_after_hwframe+0x44/0xae [ 179.188604][ T3731] ===================================================== In our case, there are two Thread A and B: Context: Thread A: Context: Thread B: l2cap_chan_timeout() __se_sys_shutdown() l2cap_chan_close() l2cap_sock_shutdown() l2cap_chan_del() l2cap_chan_close() l2cap_sock_teardown_cb() l2cap_sock_teardown_cb() Once l2cap_sock_teardown_cb() excuted, this sock will be marked as SOCK_ZAPPED, and can be treated as killable in l2cap_sock_kill() if sock_orphan() has excuted, at this time we close sock through sock_close() which end to call l2cap_sock_kill() like Thread C: Context: Thread C: sock_close() l2cap_sock_release() sock_orphan() l2cap_sock_kill() #free sock if refcnt is 1 If C completed, Once A or B reaches l2cap_sock_teardown_cb() again, use-after-free happened. We should set chan->data to NULL if sock is destructed, for telling teardown operation is not allowed in l2cap_sock_teardown_cb(), and also we should avoid killing an already killed socket in l2cap_sock_close_cb(). Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com> --- v2: put chan->data = NULL in l2cap_socl_destruct(), this refers to Luiz Augusto von Dentz <luiz.dentz@gmail.com>'s proposal. --- net/bluetooth/l2cap_sock.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)