[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c. [ 38.989526] audit: type=1800 audit(1546275588.811:25): pid=7763 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="cron" dev="sda1" ino=2414 res=0 [ 39.026234] audit: type=1800 audit(1546275588.821:26): pid=7763 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="mcstrans" dev="sda1" ino=2457 res=0 [ 39.059694] audit: type=1800 audit(1546275588.821:27): pid=7763 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 '10.128.0.45' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 47.345350] [ 47.347016] ====================================================== [ 47.353343] WARNING: possible circular locking dependency detected [ 47.359654] 4.20.0-rc7-next-20181224 #1 Not tainted [ 47.364645] ------------------------------------------------------ [ 47.370936] syz-executor051/7917 is trying to acquire lock: [ 47.376637] 000000008a21b4d3 (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 [ 47.384017] [ 47.384017] but task is already holding lock: [ 47.389994] 000000007374bdd2 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x26d0 [ 47.399338] [ 47.399338] which lock already depends on the new lock. [ 47.399338] [ 47.407628] [ 47.407628] the existing dependency chain (in reverse order) is: [ 47.415236] [ 47.415236] -> #1 (&sig->cred_guard_mutex){+.+.}: [ 47.421540] __mutex_lock+0x12f/0x1670 [ 47.425931] mutex_lock_interruptible_nested+0x16/0x20 [ 47.431725] proc_pid_attr_write+0x1fa/0x530 [ 47.436636] __vfs_write+0x116/0xb40 [ 47.440899] __kernel_write+0x110/0x3b0 [ 47.445398] write_pipe_buf+0x180/0x240 [ 47.449873] __splice_from_pipe+0x39a/0x7e0 [ 47.454693] splice_from_pipe+0x1ea/0x310 [ 47.459340] default_file_splice_write+0x3c/0x90 [ 47.464593] do_splice+0x64b/0x1410 [ 47.468732] __x64_sys_splice+0x2c6/0x330 [ 47.473384] do_syscall_64+0x1a3/0x800 [ 47.477795] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 47.483483] [ 47.483483] -> #0 (&pipe->mutex/1){+.+.}: [ 47.489109] lock_acquire+0x1db/0x570 [ 47.493412] __mutex_lock+0x12f/0x1670 [ 47.497801] mutex_lock_nested+0x16/0x20 [ 47.502377] fifo_open+0x159/0xb00 [ 47.506433] do_dentry_open+0x495/0x1230 [ 47.511006] vfs_open+0xa0/0xd0 [ 47.514836] path_openat+0x144f/0x5660 [ 47.519218] do_filp_open+0x26f/0x370 [ 47.523518] do_open_execat+0x207/0x8e0 [ 47.528027] __do_execve_file.isra.0+0x1939/0x26d0 [ 47.533509] __x64_sys_execve+0x8f/0xc0 [ 47.538000] do_syscall_64+0x1a3/0x800 [ 47.542398] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 47.548117] [ 47.548117] other info that might help us debug this: [ 47.548117] [ 47.556229] Possible unsafe locking scenario: [ 47.556229] [ 47.562271] CPU0 CPU1 [ 47.566912] ---- ---- [ 47.571552] lock(&sig->cred_guard_mutex); [ 47.575846] lock(&pipe->mutex/1); [ 47.581967] lock(&sig->cred_guard_mutex); [ 47.588783] lock(&pipe->mutex/1); [ 47.592403] [ 47.592403] *** DEADLOCK *** [ 47.592403] [ 47.598450] 1 lock held by syz-executor051/7917: [ 47.603193] #0: 000000007374bdd2 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x26d0 [ 47.612971] [ 47.612971] stack backtrace: [ 47.617456] CPU: 0 PID: 7917 Comm: syz-executor051 Not tainted 4.20.0-rc7-next-20181224 #1 [ 47.625833] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 47.635166] Call Trace: [ 47.637734] dump_stack+0x1db/0x2d0 [ 47.641361] ? dump_stack_print_info.cold+0x20/0x20 [ 47.646357] ? print_stack_trace+0x77/0xb0 [ 47.650575] ? vprintk_func+0x86/0x189 [ 47.654447] print_circular_bug.isra.0.cold+0x1cc/0x28f [ 47.659813] __lock_acquire+0x2fed/0x4a10 [ 47.663961] ? is_bpf_text_address+0xac/0x170 [ 47.668451] ? mark_held_locks+0x100/0x100 [ 47.672667] ? mark_held_locks+0xb1/0x100 [ 47.676798] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 47.681880] ? lockdep_hardirqs_on+0x415/0x5d0 [ 47.686491] ? depot_save_stack+0x1de/0x460 [ 47.690799] ? trace_hardirqs_off_caller+0x300/0x300 [ 47.695883] ? do_raw_spin_trylock+0x270/0x270 [ 47.700461] ? add_lock_to_list.isra.0+0x450/0x450 [ 47.705369] ? print_usage_bug+0xd0/0xd0 [ 47.709419] ? __lock_is_held+0xb6/0x140 [ 47.713465] lock_acquire+0x1db/0x570 [ 47.717246] ? fifo_open+0x159/0xb00 [ 47.720943] ? ___might_sleep+0x1e7/0x310 [ 47.725088] ? lock_release+0xc40/0xc40 [ 47.729045] ? fifo_open+0x159/0xb00 [ 47.732740] ? fifo_open+0x159/0xb00 [ 47.736430] __mutex_lock+0x12f/0x1670 [ 47.740298] ? fifo_open+0x159/0xb00 [ 47.743991] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 47.749510] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 47.755051] ? fifo_open+0x159/0xb00 [ 47.758746] ? lockdep_init_map+0x10c/0x5b0 [ 47.763050] ? mutex_trylock+0x2d0/0x2d0 [ 47.767104] ? add_lock_to_list.isra.0+0x450/0x450 [ 47.772015] ? __mutex_init+0x1f6/0x2a0 [ 47.775977] ? psi_task_change.cold+0x1ec/0x1ec [ 47.780626] ? fifo_open+0x2b5/0xb00 [ 47.784319] ? find_held_lock+0x35/0x120 [ 47.788375] ? fifo_open+0x2b5/0xb00 [ 47.792069] ? lock_acquire+0x1db/0x570 [ 47.796044] ? kasan_check_read+0x11/0x20 [ 47.800186] ? do_raw_spin_unlock+0xa0/0x330 [ 47.804572] ? do_raw_spin_trylock+0x270/0x270 [ 47.809135] mutex_lock_nested+0x16/0x20 [ 47.813191] ? mutex_lock_nested+0x16/0x20 [ 47.817406] fifo_open+0x159/0xb00 [ 47.820932] do_dentry_open+0x495/0x1230 [ 47.824997] ? do_raw_spin_unlock+0xa0/0x330 [ 47.829397] ? pipe_release+0x280/0x280 [ 47.833452] ? chown_common+0x740/0x740 [ 47.837408] ? security_inode_permission+0xd5/0x110 [ 47.842404] ? inode_permission+0xb4/0x570 [ 47.846618] vfs_open+0xa0/0xd0 [ 47.849878] path_openat+0x144f/0x5660 [ 47.853747] ? is_bpf_text_address+0xd3/0x170 [ 47.858223] ? path_lookupat.isra.0+0xba0/0xba0 [ 47.862874] ? __lock_acquire+0x572/0x4a10 [ 47.867091] ? kmem_cache_alloc+0x12d/0x710 [ 47.871396] ? __do_execve_file.isra.0+0x47a/0x26d0 [ 47.876391] ? __x64_sys_execve+0x8f/0xc0 [ 47.880554] ? do_syscall_64+0x1a3/0x800 [ 47.884596] ? entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 47.889940] ? add_lock_to_list.isra.0+0x450/0x450 [ 47.894854] do_filp_open+0x26f/0x370 [ 47.898636] ? may_open_dev+0x100/0x100 [ 47.902608] ? refcount_dec_and_mutex_lock+0x90/0x90 [ 47.907704] ? prepare_creds+0xa4/0x4e0 [ 47.911658] ? add_lock_to_list.isra.0+0x450/0x450 [ 47.916568] ? add_lock_to_list.isra.0+0x450/0x450 [ 47.921484] ? __do_execve_file.isra.0+0x901/0x26d0 [ 47.926527] do_open_execat+0x207/0x8e0 [ 47.930485] ? unregister_binfmt+0x2b0/0x2b0 [ 47.934872] ? kasan_check_read+0x11/0x20 [ 47.938998] ? do_raw_spin_trylock+0x270/0x270 [ 47.943563] ? __sanitizer_cov_trace_const_cmp8+0x18/0x20 [ 47.949095] __do_execve_file.isra.0+0x1939/0x26d0 [ 47.954006] ? copy_strings_kernel+0x110/0x110 [ 47.958581] ? __sanitizer_cov_trace_const_cmp8+0x18/0x20 [ 47.964122] ? strncpy_from_user+0x317/0x440 [ 47.968514] ? digsig_verify.cold+0x32/0x32 [ 47.972819] ? kmem_cache_alloc+0x341/0x710 [ 47.977122] ? do_syscall_64+0x8c/0x800 [ 47.981094] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 47.986611] ? getname_flags+0x277/0x5b0 [ 47.990652] ? trace_hardirqs_off_caller+0x300/0x300 [ 47.995733] __x64_sys_execve+0x8f/0xc0 [ 47.999689] do_syscall_64+0x1a3/0x800 [ 48.003562] ? syscall_return_slowpath+0x5f0/0x5f0 [ 48.008482] ? prepare_exit_to_usermode+0x232/0x3b0 [ 48.013478] ? trace_hardirqs_off_thunk+0x1a/0x1c [ 48.018304] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 48.023472] RIP: 0033:0x445719 [ 48.026693] Code: e8 6c b6 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 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00 [ 48.045570] RSP: 002b:00007ff67