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Message-ID: <Y70o0gPKZRCKS93n@x130> Date: Tue, 10 Jan 2023 00:58:58 -0800 From: Saeed Mahameed <saeed@...nel.org> To: Luiz Augusto von Dentz <luiz.dentz@...il.com> Cc: Ying Hsu <yinghsu@...omium.org>, linux-bluetooth@...r.kernel.org, marcel@...tmann.org, leon@...nel.org, chromeos-bluetooth-upstreaming@...omium.org, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Johan Hedberg <johan.hedberg@...il.com>, Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH v2] Bluetooth: Fix possible deadlock in rfcomm_sk_state_change On 06 Jan 11:44, Luiz Augusto von Dentz wrote: >Hi Saeed, > >On Thu, Jan 5, 2023 at 5:18 PM Saeed Mahameed <saeed@...nel.org> wrote: >> >> On 04 Jan 14:21, Luiz Augusto von Dentz wrote: >> >Hi Ying, >> > >> >On Wed, Jan 4, 2023 at 7:07 AM Ying Hsu <yinghsu@...omium.org> wrote: >> >> >> >> There's a possible deadlock when two processes are connecting >> >> and closing a RFCOMM socket concurrently. Here's the call trace: >> > >> >Are you sure it is 2 different processes? Usually that would mean 2 >> >different sockets (sk) then so they wouldn't share the same lock, so >> >this sounds more like 2 different threads, perhaps it is worth >> >creating a testing case in our rfcomm-tester so we are able to detect >> >this sort of thing in the future. >> > >> >> -> #2 (&d->lock){+.+.}-{3:3}: >> >> __mutex_lock_common kernel/locking/mutex.c:603 [inline] >> >> __mutex_lock0x12f/0x1360 kernel/locking/mutex.c:747 >> >> __rfcomm_dlc_close+0x15d/0x890 net/bluetooth/rfcomm/core.c:487 >> >> rfcomm_dlc_close+1e9/0x240 net/bluetooth/rfcomm/core.c:520 >> >> __rfcomm_sock_close+0x13c/0x250 net/bluetooth/rfcomm/sock.c:220 >> >> rfcomm_sock_shutdown+0xd8/0x230 net/bluetooth/rfcomm/sock.c:907 >> >> rfcomm_sock_release+0x68/0x140 net/bluetooth/rfcomm/sock.c:928 >> >> __sock_release+0xcd/0x280 net/socket.c:650 >> >> sock_close+0x1c/0x20 net/socket.c:1365 >> >> __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+0xaa8/0x2950 kernel/exit.c:867 >> >> do_group_exit+0xd4/0x2a0 kernel/exit.c:1012 >> >> get_signal+0x21c3/0x2450 kernel/signal.c:2859 >> >> arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306 >> >> 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 >> >> >> >> -> #1 (rfcomm_mutex){+.+.}-{3:3}: >> >> __mutex_lock_common kernel/locking/mutex.c:603 [inline] >> >> __mutex_lock+0x12f/0x1360 kernel/locking/mutex.c:747 >> >> rfcomm_dlc_open+0x93/0xa80 net/bluetooth/rfcomm/core.c:425 >> >> rfcomm_sock_connect+0x329/0x450 net/bluetooth/rfcomm/sock.c:413 >> >> __sys_connect_file+0x153/0x1a0 net/socket.c:1976 >> >> __sys_connect+0x165/0x1a0 net/socket.c:1993 >> >> __do_sys_connect net/socket.c:2003 [inline] >> >> __se_sys_connect net/socket.c:2000 [inline] >> >> __x64_sys_connect+0x73/0xb0 net/socket.c:2000 >> >> do_syscall_x64 arch/x86/entry/common.c:50 [inline] >> >> do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 >> >> entry_SYSCALL_64_after_hwframe+0x63/0xcd >> >> >> >> -> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}: >> >> check_prev_add kernel/locking/lockdep.c:3097 [inline] >> >> check_prevs_add kernel/locking/lockdep.c:3216 [inline] >> >> validate_chain kernel/locking/lockdep.c:3831 [inline] >> >> __lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055 >> >> lock_acquire kernel/locking/lockdep.c:5668 [inline] >> >> lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633 >> >> lock_sock_nested+0x3a/0xf0 net/core/sock.c:3470 >> >> lock_sock include/net/sock.h:1725 [inline] >> >> rfcomm_sk_state_change+0x6d/0x3a0 net/bluetooth/rfcomm/sock.c:73 >> >> __rfcomm_dlc_close+0x1b1/0x890 net/bluetooth/rfcomm/core.c:489 >> >> rfcomm_dlc_close+0x1e9/0x240 net/bluetooth/rfcomm/core.c:520 >> >> __rfcomm_sock_close+0x13c/0x250 net/bluetooth/rfcomm/sock.c:220 >> >> rfcomm_sock_shutdown+0xd8/0x230 net/bluetooth/rfcomm/sock.c:907 >> >> rfcomm_sock_release+0x68/0x140 net/bluetooth/rfcomm/sock.c:928 >> >> __sock_release+0xcd/0x280 net/socket.c:650 >> >> sock_close+0x1c/0x20 net/socket.c:1365 >> >> __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+0xaa8/0x2950 kernel/exit.c:867 >> >> do_group_exit+0xd4/0x2a0 kernel/exit.c:1012 >> >> get_signal+0x21c3/0x2450 kernel/signal.c:2859 >> >> arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306 >> >> 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 >> >> >> >> Signed-off-by: Ying Hsu <yinghsu@...omium.org> >> >> --- >> >> This commit has been tested with a C reproducer on qemu-x86_64 >> >> and a ChromeOS device. >> >> >> >> Changes in v2: >> >> - Fix potential use-after-free in rfc_comm_sock_connect. >> >> >> >> net/bluetooth/rfcomm/sock.c | 7 ++++++- >> >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> >> >> diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c >> >> index 21e24da4847f..4397e14ff560 100644 >> >> --- a/net/bluetooth/rfcomm/sock.c >> >> +++ b/net/bluetooth/rfcomm/sock.c >> >> @@ -391,6 +391,7 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a >> >> addr->sa_family != AF_BLUETOOTH) >> >> return -EINVAL; >> >> >> >> + sock_hold(sk); >> >> lock_sock(sk); >> >> >> >> if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) { >> >> @@ -410,14 +411,18 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a >> >> d->sec_level = rfcomm_pi(sk)->sec_level; >> >> d->role_switch = rfcomm_pi(sk)->role_switch; >> >> >> >> + /* Drop sock lock to avoid potential deadlock with the RFCOMM lock */ >> >> + release_sock(sk); >> >> err = rfcomm_dlc_open(d, &rfcomm_pi(sk)->src, &sa->rc_bdaddr, >> >> sa->rc_channel); >> >> - if (!err) >> >> + lock_sock(sk); >> >> + if (!err && !sock_flag(sk, SOCK_ZAPPED)) >> >> err = bt_sock_wait_state(sk, BT_CONNECTED, >> >> sock_sndtimeo(sk, flags & O_NONBLOCK)); >> >> >> >> done: >> >> release_sock(sk); >> >> + sock_put(sk); >> >> return err; >> >> } >> > >> >This sounds like a great solution to hold the reference and then >> >> Why do you need sock_hold/put in the same proto_ops.callback sock opts ? >> it should be guaranteed by the caller the sk will remain valid >> or if you are paranoid then sock_hold() on your proto_ops.bind() and put() >> on your proto_ops.release() > >It doesn't looks like there is a sock_hold done in the likes of >__sys_connect/__sys_connect_file so afaik it is possible that the sk >is freed in the meantime if we attempt to release and lock afterward, >and about being paranoid I guess we are past that already since with >the likes of fuzzing testing is already paranoid in itself. > My point is, if you claim that the sk can be freed from another process after you call release_sock(sk); this means it also can be free by another process before you call lock_sock(sk); so what makes the first lock_sock(sk); safe in first place ? or after you changed the code to do sock_hold(sk) what makes sock_hold(sk) safe if another process can free it before you hold it ?
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