[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c. [ 40.060325] audit: type=1800 audit(1546948113.842:25): pid=7757 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="cron" dev="sda1" ino=2414 res=0 [ 40.098114] audit: type=1800 audit(1546948113.842:26): pid=7757 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="mcstrans" dev="sda1" ino=2457 res=0 [ 40.145699] audit: type=1800 audit(1546948113.842:27): pid=7757 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="restorecond" dev="sda1" ino=2436 res=0 [....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 Warning: Permanently added '10.128.15.217' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 50.206886] [ 50.208551] ====================================================== [ 50.214843] WARNING: possible circular locking dependency detected [ 50.221135] 5.0.0-rc1+ #14 Not tainted [ 50.224995] ------------------------------------------------------ [ 50.231286] syz-executor318/7910 is trying to acquire lock: [ 50.236982] 00000000c19a1a38 (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 [ 50.244348] [ 50.244348] but task is already holding lock: [ 50.250292] 000000007e40cac3 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x2700 [ 50.259634] [ 50.259634] which lock already depends on the new lock. [ 50.259634] [ 50.267928] [ 50.267928] the existing dependency chain (in reverse order) is: [ 50.275560] [ 50.275560] -> #1 (&sig->cred_guard_mutex){+.+.}: [ 50.281883] __mutex_lock+0x12f/0x1670 [ 50.286274] mutex_lock_interruptible_nested+0x16/0x20 [ 50.292059] proc_pid_attr_write+0x1fa/0x530 [ 50.296986] __vfs_write+0x116/0xb40 [ 50.301199] __kernel_write+0x110/0x3b0 [ 50.305687] write_pipe_buf+0x180/0x240 [ 50.310160] __splice_from_pipe+0x39a/0x7e0 [ 50.314980] splice_from_pipe+0x1ea/0x310 [ 50.319628] default_file_splice_write+0x3c/0x90 [ 50.324884] do_splice+0x64b/0x1410 [ 50.329031] __x64_sys_splice+0x2c6/0x330 [ 50.333706] do_syscall_64+0x1a3/0x800 [ 50.338097] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 50.343783] [ 50.343783] -> #0 (&pipe->mutex/1){+.+.}: [ 50.349393] lock_acquire+0x1db/0x570 [ 50.353707] __mutex_lock+0x12f/0x1670 [ 50.358114] mutex_lock_nested+0x16/0x20 [ 50.362679] fifo_open+0x159/0xb00 [ 50.366717] do_dentry_open+0x48a/0x1210 [ 50.371274] vfs_open+0xa0/0xd0 [ 50.375072] path_openat+0x144f/0x5650 [ 50.379466] do_filp_open+0x26f/0x370 [ 50.383763] do_open_execat+0x20e/0x930 [ 50.388234] __do_execve_file.isra.0+0x1966/0x2700 [ 50.393661] __x64_sys_execve+0x8f/0xc0 [ 50.398135] do_syscall_64+0x1a3/0x800 [ 50.402523] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 50.408207] [ 50.408207] other info that might help us debug this: [ 50.408207] [ 50.416338] Possible unsafe locking scenario: [ 50.416338] [ 50.422370] CPU0 CPU1 [ 50.427034] ---- ---- [ 50.431709] lock(&sig->cred_guard_mutex); [ 50.436024] lock(&pipe->mutex/1); [ 50.442163] lock(&sig->cred_guard_mutex); [ 50.448973] lock(&pipe->mutex/1); [ 50.452575] [ 50.452575] *** DEADLOCK *** [ 50.452575] [ 50.458607] 1 lock held by syz-executor318/7910: [ 50.463350] #0: 000000007e40cac3 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x2700 [ 50.473142] [ 50.473142] stack backtrace: [ 50.477617] CPU: 0 PID: 7910 Comm: syz-executor318 Not tainted 5.0.0-rc1+ #14 [ 50.484864] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 50.494195] Call Trace: [ 50.496780] dump_stack+0x1db/0x2d0 [ 50.500386] ? dump_stack_print_info.cold+0x20/0x20 [ 50.505386] ? print_stack_trace+0x77/0xb0 [ 50.509619] ? vprintk_func+0x86/0x189 [ 50.513489] print_circular_bug.isra.0.cold+0x1cc/0x28f [ 50.518832] __lock_acquire+0x3014/0x4a30 [ 50.522958] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.527866] ? is_bpf_text_address+0xac/0x170 [ 50.532345] ? mark_held_locks+0x100/0x100 [ 50.536558] ? mark_held_locks+0xb1/0x100 [ 50.540688] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 50.545770] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 50.550903] ? lockdep_hardirqs_on+0x415/0x5d0 [ 50.555477] ? trace_hardirqs_off_caller+0x300/0x300 [ 50.560557] ? do_raw_spin_trylock+0x270/0x270 [ 50.565122] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.570031] ? print_usage_bug+0xd0/0xd0 [ 50.574078] ? _raw_spin_unlock_irqrestore+0xa4/0xe0 [ 50.579162] ? __lock_is_held+0xb6/0x140 [ 50.583219] lock_acquire+0x1db/0x570 [ 50.587001] ? fifo_open+0x159/0xb00 [ 50.590692] ? ___might_sleep+0x1e7/0x310 [ 50.594816] ? lock_release+0xc40/0xc40 [ 50.598775] ? fifo_open+0x159/0xb00 [ 50.602468] ? fifo_open+0x159/0xb00 [ 50.606162] __mutex_lock+0x12f/0x1670 [ 50.610038] ? fifo_open+0x159/0xb00 [ 50.613769] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 50.619283] ? fifo_open+0x159/0xb00 [ 50.622977] ? check_preemption_disabled+0x48/0x290 [ 50.627971] ? lockdep_init_map+0x10c/0x5b0 [ 50.632269] ? mutex_trylock+0x2d0/0x2d0 [ 50.636308] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.641234] ? __mutex_init+0x1f6/0x2a0 [ 50.645194] ? psi_task_change.cold+0x1ec/0x1ec [ 50.649854] ? fifo_open+0x2b5/0xb00 [ 50.653546] ? find_held_lock+0x35/0x120 [ 50.657586] ? fifo_open+0x2b5/0xb00 [ 50.661277] ? lock_acquire+0x1db/0x570 [ 50.665234] ? kasan_check_read+0x11/0x20 [ 50.669361] ? do_raw_spin_unlock+0xa0/0x330 [ 50.673750] ? do_raw_spin_trylock+0x270/0x270 [ 50.678310] mutex_lock_nested+0x16/0x20 [ 50.682350] ? _raw_spin_unlock+0x2d/0x50 [ 50.686490] ? mutex_lock_nested+0x16/0x20 [ 50.690703] fifo_open+0x159/0xb00 [ 50.694228] do_dentry_open+0x48a/0x1210 [ 50.698269] ? pipe_release+0x280/0x280 [ 50.702225] ? chown_common+0x740/0x740 [ 50.706189] ? security_inode_permission+0xd5/0x110 [ 50.711188] ? inode_permission+0xb4/0x570 [ 50.715414] vfs_open+0xa0/0xd0 [ 50.718687] path_openat+0x144f/0x5650 [ 50.722577] ? is_bpf_text_address+0xd3/0x170 [ 50.727064] ? path_lookupat.isra.0+0xba0/0xba0 [ 50.731716] ? __lock_acquire+0x572/0x4a30 [ 50.735933] ? kmem_cache_alloc+0x12d/0x710 [ 50.740241] ? __do_execve_file.isra.0+0x47a/0x2700 [ 50.745266] ? __x64_sys_execve+0x8f/0xc0 [ 50.749413] ? do_syscall_64+0x1a3/0x800 [ 50.753472] ? entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 50.758815] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.763725] do_filp_open+0x26f/0x370 [ 50.767516] ? may_open_dev+0x100/0x100 [ 50.771468] ? refcount_add_not_zero_checked+0x330/0x330 [ 50.776901] ? prepare_creds+0xa4/0x4e0 [ 50.780870] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.785808] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.790721] ? __do_execve_file.isra.0+0x901/0x2700 [ 50.795718] do_open_execat+0x20e/0x930 [ 50.799673] ? unregister_binfmt+0x2b0/0x2b0 [ 50.804068] ? kasan_check_read+0x11/0x20 [ 50.808217] ? do_raw_spin_trylock+0x270/0x270 [ 50.812811] ? __phys_addr_symbol+0x30/0x70 [ 50.817124] __do_execve_file.isra.0+0x1966/0x2700 [ 50.822059] ? copy_strings_kernel+0x110/0x110 [ 50.826654] ? __sanitizer_cov_trace_const_cmp8+0x18/0x20 [ 50.832174] ? strncpy_from_user+0x3aa/0x4e0 [ 50.836563] ? digsig_verify.cold+0x32/0x32 [ 50.840864] ? kmem_cache_alloc+0x341/0x710 [ 50.845170] ? do_syscall_64+0x8c/0x800 [ 50.849131] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 50.854647] ? getname_flags+0x277/0x5b0 [ 50.858686] ? trace_hardirqs_off_caller+0x300/0x300 [ 50.863768] __x64_sys_execve+0x8f/0xc0 [ 50.867725] do_syscall_64+0x1a3/0x800 [ 50.871592] ? syscall_return_slowpath+0x5f0/0x5f0 [ 50.876504] ? prepare_exit_to_usermode+0x3b0/0x3b0 [ 50.881499] ? __switch_to_asm+0x34/0x70 [ 50.885555] ? trace_hardirqs_off_thunk+0x1a/0x1c [ 50.890417] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 50.895588] RIP: 0033:0x445709 [ 50.898763] Code: e8 ec b8 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 8b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00 [ 50.917642] RSP: 002b:00007fdfabb1ad18 EFLAGS: 00000246 ORIG_RAX: 000000000000003b [ 50.925327] RAX: ffffffffffffffda RBX: 00000000006dac58 RCX: 0000000000445709 [ 50.932577] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000040 [ 50.939822] RBP: 00000000006dac50 R08: 68742f636f72702f R09: 68742f636f72702f [ 50.947072] R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac5c [ 50.954318] R13: 00007fdfabb1ad20 R14: 0030656c69662f2e R15: 0000