[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c. [ 40.904631] audit: type=1800 audit(1546948104.936:25): pid=7828 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="cron" dev="sda1" ino=2414 res=0 [ 40.941033] audit: type=1800 audit(1546948104.946:26): pid=7828 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="mcstrans" dev="sda1" ino=2457 res=0 [ 40.968640] audit: type=1800 audit(1546948104.946:27): pid=7828 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 '10.128.10.15' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 51.761340] [ 51.762994] ====================================================== [ 51.769288] WARNING: possible circular locking dependency detected [ 51.775582] 5.0.0-rc1+ #14 Not tainted [ 51.779461] ------------------------------------------------------ [ 51.785759] syz-executor490/7982 is trying to acquire lock: [ 51.791445] 000000001d466ab6 (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 [ 51.798800] [ 51.798800] but task is already holding lock: [ 51.804748] 0000000000d1e274 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x2700 [ 51.814096] [ 51.814096] which lock already depends on the new lock. [ 51.814096] [ 51.822387] [ 51.822387] the existing dependency chain (in reverse order) is: [ 51.829986] [ 51.829986] -> #1 (&sig->cred_guard_mutex){+.+.}: [ 51.836305] __mutex_lock+0x12f/0x1670 [ 51.840699] mutex_lock_interruptible_nested+0x16/0x20 [ 51.846478] proc_pid_attr_write+0x1fa/0x530 [ 51.851392] __vfs_write+0x116/0xb40 [ 51.855610] __kernel_write+0x110/0x3b0 [ 51.860094] write_pipe_buf+0x180/0x240 [ 51.864571] __splice_from_pipe+0x39a/0x7e0 [ 51.869400] splice_from_pipe+0x1ea/0x310 [ 51.874050] default_file_splice_write+0x3c/0x90 [ 51.879321] do_splice+0x64b/0x1410 [ 51.883447] __ia32_sys_splice+0x2c4/0x330 [ 51.888186] do_fast_syscall_32+0x333/0xf98 [ 51.893013] entry_SYSENTER_compat+0x70/0x7f [ 51.897917] [ 51.897917] -> #0 (&pipe->mutex/1){+.+.}: [ 51.903553] lock_acquire+0x1db/0x570 [ 51.907854] __mutex_lock+0x12f/0x1670 [ 51.912240] mutex_lock_nested+0x16/0x20 [ 51.916805] fifo_open+0x159/0xb00 [ 51.920844] do_dentry_open+0x48a/0x1210 [ 51.925419] vfs_open+0xa0/0xd0 [ 51.929201] path_openat+0x144f/0x5650 [ 51.933589] do_filp_open+0x26f/0x370 [ 51.937893] do_open_execat+0x20e/0x930 [ 51.942367] __do_execve_file.isra.0+0x1966/0x2700 [ 51.947796] __ia32_compat_sys_execve+0x94/0xc0 [ 51.952979] do_fast_syscall_32+0x333/0xf98 [ 51.957803] entry_SYSENTER_compat+0x70/0x7f [ 51.962707] [ 51.962707] other info that might help us debug this: [ 51.962707] [ 51.970820] Possible unsafe locking scenario: [ 51.970820] [ 51.976860] CPU0 CPU1 [ 51.981502] ---- ---- [ 51.986144] lock(&sig->cred_guard_mutex); [ 51.990458] lock(&pipe->mutex/1); [ 51.996586] lock(&sig->cred_guard_mutex); [ 52.003432] lock(&pipe->mutex/1); [ 52.007043] [ 52.007043] *** DEADLOCK *** [ 52.007043] [ 52.013079] 1 lock held by syz-executor490/7982: [ 52.017808] #0: 0000000000d1e274 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x2700 [ 52.027597] [ 52.027597] stack backtrace: [ 52.032072] CPU: 0 PID: 7982 Comm: syz-executor490 Not tainted 5.0.0-rc1+ #14 [ 52.039496] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 52.048827] Call Trace: [ 52.051402] dump_stack+0x1db/0x2d0 [ 52.055010] ? dump_stack_print_info.cold+0x20/0x20 [ 52.060012] ? print_stack_trace+0x77/0xb0 [ 52.064228] ? vprintk_func+0x86/0x189 [ 52.068099] print_circular_bug.isra.0.cold+0x1cc/0x28f [ 52.073456] __lock_acquire+0x3014/0x4a30 [ 52.077586] ? add_lock_to_list.isra.0+0x450/0x450 [ 52.082498] ? is_bpf_text_address+0xac/0x170 [ 52.086978] ? mark_held_locks+0x100/0x100 [ 52.091194] ? mark_held_locks+0xb1/0x100 [ 52.095344] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 52.100426] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 52.105515] ? lockdep_hardirqs_on+0x415/0x5d0 [ 52.110081] ? trace_hardirqs_off_caller+0x300/0x300 [ 52.115165] ? do_raw_spin_trylock+0x270/0x270 [ 52.119779] ? add_lock_to_list.isra.0+0x450/0x450 [ 52.124692] ? print_usage_bug+0xd0/0xd0 [ 52.128734] ? _raw_spin_unlock_irqrestore+0xa4/0xe0 [ 52.133817] ? __lock_is_held+0xb6/0x140 [ 52.137903] lock_acquire+0x1db/0x570 [ 52.141696] ? fifo_open+0x159/0xb00 [ 52.145390] ? ___might_sleep+0x1e7/0x310 [ 52.149522] ? lock_release+0xc40/0xc40 [ 52.153478] ? fifo_open+0x159/0xb00 [ 52.157172] ? fifo_open+0x159/0xb00 [ 52.160880] __mutex_lock+0x12f/0x1670 [ 52.164756] ? fifo_open+0x159/0xb00 [ 52.168463] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 52.173992] ? fifo_open+0x159/0xb00 [ 52.177709] ? check_preemption_disabled+0x48/0x290 [ 52.182706] ? lockdep_init_map+0x10c/0x5b0 [ 52.187011] ? mutex_trylock+0x2d0/0x2d0 [ 52.191051] ? add_lock_to_list.isra.0+0x450/0x450 [ 52.195960] ? __mutex_init+0x1f6/0x2a0 [ 52.199917] ? psi_task_change.cold+0x1ec/0x1ec [ 52.204566] ? fifo_open+0x2b5/0xb00 [ 52.208267] ? find_held_lock+0x35/0x120 [ 52.212309] ? fifo_open+0x2b5/0xb00 [ 52.216006] ? lock_acquire+0x1db/0x570 [ 52.219964] ? kasan_check_read+0x11/0x20 [ 52.224092] ? do_raw_spin_unlock+0xa0/0x330 [ 52.228481] ? do_raw_spin_trylock+0x270/0x270 [ 52.233048] mutex_lock_nested+0x16/0x20 [ 52.237094] ? _raw_spin_unlock+0x2d/0x50 [ 52.241221] ? mutex_lock_nested+0x16/0x20 [ 52.245435] fifo_open+0x159/0xb00 [ 52.248967] do_dentry_open+0x48a/0x1210 [ 52.253014] ? pipe_release+0x280/0x280 [ 52.256968] ? chown_common+0x740/0x740 [ 52.260923] ? security_inode_permission+0xd5/0x110 [ 52.265919] ? inode_permission+0xb4/0x570 [ 52.270147] vfs_open+0xa0/0xd0 [ 52.273409] path_openat+0x144f/0x5650 [ 52.277284] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 52.282398] ? lockdep_hardirqs_on+0x415/0x5d0 [ 52.286963] ? trace_hardirqs_on+0xbd/0x310 [ 52.291269] ? path_lookupat.isra.0+0xba0/0xba0 [ 52.295921] ? depot_save_stack+0x1de/0x460 [ 52.300227] ? __lock_acquire+0x572/0x4a30 [ 52.304442] ? kmem_cache_alloc+0x12d/0x710 [ 52.308746] ? __do_execve_file.isra.0+0x47a/0x2700 [ 52.313741] ? __ia32_compat_sys_execve+0x94/0xc0 [ 52.318565] ? do_fast_syscall_32+0x333/0xf98 [ 52.323042] ? entry_SYSENTER_compat+0x70/0x7f [ 52.327604] ? add_lock_to_list.isra.0+0x450/0x450 [ 52.332513] do_filp_open+0x26f/0x370 [ 52.336322] ? may_open_dev+0x100/0x100 [ 52.340279] ? refcount_add_not_zero_checked+0x330/0x330 [ 52.345715] ? prepare_creds+0xa4/0x4e0 [ 52.349677] ? add_lock_to_list.isra.0+0x450/0x450 [ 52.354588] ? add_lock_to_list.isra.0+0x450/0x450 [ 52.359515] ? __do_execve_file.isra.0+0x901/0x2700 [ 52.364511] do_open_execat+0x20e/0x930 [ 52.368484] ? unregister_binfmt+0x2b0/0x2b0 [ 52.372874] ? kasan_check_read+0x11/0x20 [ 52.377028] ? do_raw_spin_trylock+0x270/0x270 [ 52.381595] ? __phys_addr_symbol+0x30/0x70 [ 52.385902] __do_execve_file.isra.0+0x1966/0x2700 [ 52.390831] ? copy_strings_kernel+0x110/0x110 [ 52.395394] ? __sanitizer_cov_trace_const_cmp8+0x18/0x20 [ 52.400925] ? strncpy_from_user+0x3aa/0x4e0 [ 52.405316] ? digsig_verify.cold+0x32/0x32 [ 52.409620] ? kmem_cache_alloc+0x341/0x710 [ 52.413920] ? do_fast_syscall_32+0x13b/0xf98 [ 52.418400] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 52.423917] ? getname_flags+0x277/0x5b0 [ 52.427960] ? trace_hardirqs_off_caller+0x300/0x300 [ 52.433060] __ia32_compat_sys_execve+0x94/0xc0 [ 52.437732] do_fast_syscall_32+0x333/0xf98 [ 52.442035] ? do_int80_syscall_32+0x880/0x880 [ 52.446594] ? trace_hardirqs_off+0x310/0x310 [ 52.451085] ? syscall_return_slowpath+0x3b0/0x5f0 [ 52.455996] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 52.461529] ? prepare_exit_to_usermode+0x232/0x3b0 [ 52.466525] ? trace_hardirqs_off_thunk+0x1a/0x1c [ 52.471364] entry_SYSENTER_compat+0x70/0x7f [ 52.475766] RIP: 0023:0xf7fdf869 [ 52.479115] Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 [ 52.498011] RSP: 002b:00000000f7fba15c EFLAGS: 00000246 ORIG_RAX: 000000000000000b [ 52.505697] RAX: ffffffffffffffda RBX: 0000000020000040 RCX: 0000000000000000 [ 52.512944] RDX: