Messages in this thread | | | Subject | Re: [PATCH] Bluetooth: fix use-after-free error in lock_sock_nested() | From | "Wangshaobo (bobo)" <> | Date | Fri, 16 Jul 2021 09:37:57 +0800 |
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在 2021/7/15 12:57, Wangshaobo (bobo) 写道: > > 在 2021/7/15 5:50, Luiz Augusto von Dentz 写道: >> Hi, >> >> On Tue, Jul 13, 2021 at 8:20 PM Wang ShaoBo >> <bobo.shaobowang@huawei.com> wrote: >>> 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 freed, 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> >>> --- >>> net/bluetooth/l2cap_sock.c | 14 ++++++++++++-- >>> 1 file changed, 12 insertions(+), 2 deletions(-) >>> >>> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c >>> index c99d65ef13b1..ddc6a692b237 100644 >>> --- a/net/bluetooth/l2cap_sock.c >>> +++ b/net/bluetooth/l2cap_sock.c >>> @@ -1215,14 +1215,18 @@ static int l2cap_sock_recvmsg(struct socket >>> *sock, struct msghdr *msg, >>> */ >>> static void l2cap_sock_kill(struct sock *sk) >>> { >>> + struct l2cap_chan *chan; >>> + >>> if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket) >>> return; >>> >>> BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state)); >>> >>> /* Kill poor orphan */ >>> - >>> - l2cap_chan_put(l2cap_pi(sk)->chan); >>> + chan = l2cap_pi(sk)->chan; >>> + l2cap_chan_put(chan); > > There is a problem here, the above sentence `l2cap_chan_put(chan)` > should put after > > following sentence. > >>> + if (refcount_read(&sk->sk_refcnt) == 1) >>> + chan->data = NULL; >> Instead of checking if it is the last reference here, wouldn't it be >> better to reset the chan->data to NULL on l2cap_sock_destruct? > > Hi, > > In my case it looks OK, this is the diff: > > diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c > index f1b1edd0b697..32ef3328ab49 100644 > --- a/net/bluetooth/l2cap_sock.c > +++ b/net/bluetooth/l2cap_sock.c > @@ -1500,6 +1500,9 @@ static void l2cap_sock_close_cb(struct > l2cap_chan *chan) > { > struct sock *sk = chan->data; > > + if (!sk) > + return; > + > l2cap_sock_kill(sk); > } > > @@ -1508,6 +1511,9 @@ 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) > @@ -1700,6 +1706,7 @@ static void l2cap_sock_destruct(struct sock *sk) > BT_DBG("sk %p", sk); > > if (l2cap_pi(sk)->chan) > + l2cap_pi(sk)->chan->data = NULL; > l2cap_chan_put(l2cap_pi(sk)->chan); > > But if it has potential risk if l2cap_sock_destruct() can not be > excuted in time ? > > sk_free(): > > if (refcount_dec_and_test(&sk->sk_wmem_alloc)) //is possible > this condition false ? > > __sk_free(sk) -> ... l2cap_sock_destruct() > Dear Luiz,
Not only that, if l2cap_sock_kill() has put 'l2cap_pi(sk)->chan', how does we avoid re-puting 'l2cap_pi(sk)->chan' if l2cap_sock_destruct() work postponed? this will cause underflow of chan->refcount; this PATCH 4e1a720d0312 ("Bluetooth: avoid killing an already killed socket") also may not work in any case because only sock_orphan() has excuted can this sock be killed, but if sco_sock_release() excute first, for this sock has been marked as SOCK_DEAD, this sock can never be killed. So should we think put chan->data = NULL in xx_sock_kill() is a better choice ?
- WangShaoBo
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