Hi, I believe the deadlock is more than possible but actually real. I got a poc that could stably trigger the deadlock. poc: https://drive.google.com/file/d/1PjqvMtHsrrGM1MIRGKl_zJGR-teAMMQy/view?usp=sharing Description/Root cause: In rfcomm_sock_shutdown(), lock_sock() is called when releasing and shutting down socket. However, lock_sock() has to be called once more when the sk_state is changed because the lock is not always held when rfcomm_sk_state_change() is called. One such call stack is: rfcomm_sock_shutdown(): lock_sock(); __rfcomm_sock_close(): rfcomm_dlc_close(): __rfcomm_dlc_close(): rfcomm_dlc_lock(); rfcomm_sk_state_change(): lock_sock(); Besides the recursive deadlock, there is also an issue of a lock hierarchy inversion between rfcomm_dlc_lock() and lock_sock() if the socket is locked in rfcomm_sk_state_change(). Reference: https://lore.kernel.org/all/20211004180734.434511-1-desmondcheongzx@xxxxxxxxx/ On Sun, Aug 28, 2022 at 12:19 AM Jiacheng Xu <578001344xu@xxxxxxxxx> wrote: > > Hello, > > When using modified Syzkaller to fuzz the Linux kernel-5.19, the > following crash was triggered. > We would appreciate a CVE ID if this is a security issue. > > HEAD commit: 3d7cb6b04c3f Linux-5.19 > git tree: upstream > > console output: > https://drive.google.com/file/d/1NmOGWcfPnY2kSrS0nOwvG1AZ923jFQ3p/view?usp=sharing > kernel config: https://drive.google.com/file/d/1wgIUDwP5ho29AM-K7HhysSTfWFpfXYkG/view?usp=sharing > syz repro: https://drive.google.com/file/d/16hUTEGw4IcPQA9CZvoF7I5la42TlU-Cx/view?usp=sharing > C reproducer: https://drive.google.com/file/d/1YvgzTvV4qaSZPiD4D1IWGL4GuapzHD2w/view?usp=sharing > > Environment: > Ubuntu 20.04 on Linux 5.4.0 > QEMU 4.2.1: > qemu-system-x86_64 \ > -m 2G \ > -smp 2 \ > -kernel /home/workdir/bzImage \ > -append "console=ttyS0 root=/dev/sda earlyprintk=serial net.ifnames=0" \ > -drive file=/home/workdir/stretch.img,format=raw \ > -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \ > -net nic,model=e1000 \ > -enable-kvm \ > -nographic \ > -pidfile vm.pid \ > 2>&1 | tee vm.log > > If you fix this issue, please add the following tag to the commit: > Reported-by Jiacheng Xu<578001344xu@xxxxxxxxx> > > ============================================ > WARNING: possible recursive locking detected > 5.19.0 #1 Not tainted > -------------------------------------------- > syz-executor/9064 is trying to acquire lock: > ffff888026b13130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, > at: lock_sock include/net/sock.h:1677 [inline] > ffff888026b13130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, > at: rfcomm_sk_state_change+0x6e/0x3a0 net/bluetooth/rfcomm/sock.c:73 > > but task is already holding lock: > ffff888026b13130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, > at: lock_sock include/net/sock.h:1677 [inline] > ffff888026b13130 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, > at: rfcomm_sock_shutdown+0x57/0x220 net/bluetooth/rfcomm/sock.c:902 > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock(sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM); > lock(sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM); > > *** DEADLOCK *** > > May be due to missing lock nesting notation > > 4 locks held by syz-executor/9064: > #0: ffff888110dac410 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: > inode_lock include/linux/fs.h:741 [inline] > #0: ffff888110dac410 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: > __sock_release+0x86/0x280 net/socket.c:649 > #1: ffff888026b13130 > (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: lock_sock > include/net/sock.h:1677 [inline] > #1: ffff888026b13130 > (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}, at: > rfcomm_sock_shutdown+0x57/0x220 net/bluetooth/rfcomm/sock.c:902 > #2: ffffffff8d7d8428 (rfcomm_mutex){+.+.}-{3:3}, at: > rfcomm_dlc_close+0x34/0x240 net/bluetooth/rfcomm/core.c:507 > #3: ffff8880155d2d28 (&d->lock){+.+.}-{3:3}, at: > __rfcomm_dlc_close+0x157/0x710 net/bluetooth/rfcomm/core.c:487 > > stack backtrace: > CPU: 0 PID: 9064 Comm: syz-executor Not tainted 5.19.0 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > 1.13.0-1ubuntu1.1 04/01/2014 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 > print_deadlock_bug kernel/locking/lockdep.c:2988 [inline] > check_deadlock kernel/locking/lockdep.c:3031 [inline] > validate_chain kernel/locking/lockdep.c:3816 [inline] > __lock_acquire.cold+0x152/0x3ca kernel/locking/lockdep.c:5053 > lock_acquire kernel/locking/lockdep.c:5665 [inline] > lock_acquire+0x1ab/0x580 kernel/locking/lockdep.c:5630 > lock_sock_nested+0x36/0xf0 net/core/sock.c:3389 > lock_sock include/net/sock.h:1677 [inline] > rfcomm_sk_state_change+0x6e/0x3a0 net/bluetooth/rfcomm/sock.c:73 > __rfcomm_dlc_close+0x1ab/0x710 net/bluetooth/rfcomm/core.c:489 > rfcomm_dlc_close+0x1ea/0x240 net/bluetooth/rfcomm/core.c:520 > __rfcomm_sock_close+0xda/0x260 net/bluetooth/rfcomm/sock.c:220 > rfcomm_sock_shutdown+0xf4/0x220 net/bluetooth/rfcomm/sock.c:905 > rfcomm_sock_release+0x5f/0x140 net/bluetooth/rfcomm/sock.c:925 > __sock_release+0xcd/0x280 net/socket.c:650 > sock_close+0x18/0x20 net/socket.c:1365 > __fput+0x277/0x9d0 fs/file_table.c:317 > task_work_run+0xe0/0x1a0 kernel/task_work.c:177 > exit_task_work include/linux/task_work.h:38 [inline] > do_exit+0xaf5/0x2da0 kernel/exit.c:795 > do_group_exit+0xd2/0x2f0 kernel/exit.c:925 > get_signal+0x2842/0x2870 kernel/signal.c:2857 > arch_do_signal_or_restart+0x82/0x2270 arch/x86/kernel/signal.c:869 > exit_to_user_mode_loop kernel/entry/common.c:166 [inline] > exit_to_user_mode_prepare+0x174/0x260 kernel/entry/common.c:201 > __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline] > syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:294 > do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > RIP: 0033:0x7f26c3295dfd > Code: Unable to access opcode bytes at RIP 0x7f26c3295dd3. > RSP: 002b:00007f26c43fcc58 EFLAGS: 00000246 ORIG_RAX: 000000000000002a > RAX: fffffffffffffffc RBX: 00007f26c33bc0a0 RCX: 00007f26c3295dfd > RDX: 0000000000000080 RSI: 0000000020000000 RDI: 0000000000000004 > RBP: 00007f26c32ff4c1 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f26c33bc0a0 > R13: 00007ffc2c88f2df R14: 00007ffc2c88f480 R15: 00007f26c43fcdc0 > </TASK>
