[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c. [ 41.439706] audit: type=1800 audit(1546948106.208:25): pid=7917 uid=0 auid=4294967295 ses=4294967295 subj=_ op=collect_data cause=failed(directio) comm="startpar" name="cron" dev="sda1" ino=2414 res=0 [ 41.475520] audit: type=1800 audit(1546948106.208:26): pid=7917 uid=0 auid=4294967295 ses=4294967295 subj=_ op=collect_data cause=failed(directio) comm="startpar" name="mcstrans" dev="sda1" ino=2457 res=0 [ 41.497680] audit: type=1800 audit(1546948106.208:27): pid=7917 uid=0 auid=4294967295 ses=4294967295 subj=_ 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 '10.128.0.55' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 50.406542] [ 50.408196] ====================================================== [ 50.414492] WARNING: possible circular locking dependency detected [ 50.420801] 5.0.0-rc1+ #14 Not tainted [ 50.424664] ------------------------------------------------------ [ 50.430964] syz-executor449/8069 is trying to acquire lock: [ 50.436649] 0000000026be8a53 (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 [ 50.444034] [ 50.444034] but task is already holding lock: [ 50.449977] 000000007e598e54 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x2700 [ 50.459320] [ 50.459320] which lock already depends on the new lock. [ 50.459320] [ 50.467610] [ 50.467610] the existing dependency chain (in reverse order) is: [ 50.475203] [ 50.475203] -> #1 (&sig->cred_guard_mutex){+.+.}: [ 50.481513] __mutex_lock+0x12f/0x1670 [ 50.485919] mutex_lock_interruptible_nested+0x16/0x20 [ 50.491710] proc_pid_attr_write+0x1fa/0x530 [ 50.496650] __vfs_write+0x116/0xb40 [ 50.500887] __kernel_write+0x110/0x3b0 [ 50.505363] write_pipe_buf+0x180/0x240 [ 50.509864] __splice_from_pipe+0x39a/0x7e0 [ 50.514700] splice_from_pipe+0x1ea/0x310 [ 50.519350] default_file_splice_write+0x3c/0x90 [ 50.524635] do_splice+0x64b/0x1410 [ 50.528762] __x64_sys_splice+0x2c6/0x330 [ 50.533422] do_syscall_64+0x1a3/0x800 [ 50.537813] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 50.543496] [ 50.543496] -> #0 (&pipe->mutex/1){+.+.}: [ 50.549113] lock_acquire+0x1db/0x570 [ 50.553456] __mutex_lock+0x12f/0x1670 [ 50.557850] mutex_lock_nested+0x16/0x20 [ 50.562410] fifo_open+0x159/0xb00 [ 50.566454] do_dentry_open+0x48a/0x1210 [ 50.571016] vfs_open+0xa0/0xd0 [ 50.574798] path_openat+0x144f/0x5650 [ 50.579184] do_filp_open+0x26f/0x370 [ 50.583488] do_open_execat+0x20e/0x930 [ 50.587960] __do_execve_file.isra.0+0x1966/0x2700 [ 50.593395] __x64_sys_execve+0x8f/0xc0 [ 50.597867] do_syscall_64+0x1a3/0x800 [ 50.602273] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 50.607957] [ 50.607957] other info that might help us debug this: [ 50.607957] [ 50.616070] Possible unsafe locking scenario: [ 50.616070] [ 50.622099] CPU0 CPU1 [ 50.626735] ---- ---- [ 50.631382] lock(&sig->cred_guard_mutex); [ 50.635678] lock(&pipe->mutex/1); [ 50.641796] lock(&sig->cred_guard_mutex); [ 50.648629] lock(&pipe->mutex/1); [ 50.652232] [ 50.652232] *** DEADLOCK *** [ 50.652232] [ 50.658264] 1 lock held by syz-executor449/8069: [ 50.662993] #0: 000000007e598e54 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x45d/0x2700 [ 50.672784] [ 50.672784] stack backtrace: [ 50.677273] CPU: 0 PID: 8069 Comm: syz-executor449 Not tainted 5.0.0-rc1+ #14 [ 50.684522] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 50.693864] Call Trace: [ 50.696434] dump_stack+0x1db/0x2d0 [ 50.700046] ? dump_stack_print_info.cold+0x20/0x20 [ 50.705039] ? print_stack_trace+0x77/0xb0 [ 50.709260] ? vprintk_func+0x86/0x189 [ 50.713129] print_circular_bug.isra.0.cold+0x1cc/0x28f [ 50.718485] __lock_acquire+0x3014/0x4a30 [ 50.722613] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.727537] ? is_bpf_text_address+0xac/0x170 [ 50.732033] ? mark_held_locks+0x100/0x100 [ 50.736244] ? mark_held_locks+0xb1/0x100 [ 50.740393] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 50.745475] ? _raw_spin_unlock_irqrestore+0x6b/0xe0 [ 50.750560] ? lockdep_hardirqs_on+0x415/0x5d0 [ 50.755126] ? trace_hardirqs_off_caller+0x300/0x300 [ 50.760207] ? do_raw_spin_trylock+0x270/0x270 [ 50.764767] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.769678] ? print_usage_bug+0xd0/0xd0 [ 50.773745] ? _raw_spin_unlock_irqrestore+0xa4/0xe0 [ 50.778825] ? __lock_is_held+0xb6/0x140 [ 50.783027] lock_acquire+0x1db/0x570 [ 50.786818] ? fifo_open+0x159/0xb00 [ 50.790513] ? ___might_sleep+0x1e7/0x310 [ 50.794643] ? lock_release+0xc40/0xc40 [ 50.798630] ? fifo_open+0x159/0xb00 [ 50.802324] ? fifo_open+0x159/0xb00 [ 50.806013] __mutex_lock+0x12f/0x1670 [ 50.809878] ? fifo_open+0x159/0xb00 [ 50.813576] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 50.819109] ? fifo_open+0x159/0xb00 [ 50.822807] ? check_preemption_disabled+0x48/0x290 [ 50.827814] ? lockdep_init_map+0x10c/0x5b0 [ 50.832129] ? mutex_trylock+0x2d0/0x2d0 [ 50.836170] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.841087] ? __mutex_init+0x1f6/0x2a0 [ 50.845042] ? psi_task_change.cold+0x1ec/0x1ec [ 50.849691] ? fifo_open+0x2b5/0xb00 [ 50.853401] ? find_held_lock+0x35/0x120 [ 50.857474] ? fifo_open+0x2b5/0xb00 [ 50.861168] ? lock_acquire+0x1db/0x570 [ 50.865123] ? kasan_check_read+0x11/0x20 [ 50.869251] ? do_raw_spin_unlock+0xa0/0x330 [ 50.873653] ? do_raw_spin_trylock+0x270/0x270 [ 50.878212] mutex_lock_nested+0x16/0x20 [ 50.882267] ? _raw_spin_unlock+0x2d/0x50 [ 50.886410] ? mutex_lock_nested+0x16/0x20 [ 50.890624] fifo_open+0x159/0xb00 [ 50.894143] do_dentry_open+0x48a/0x1210 [ 50.898181] ? pipe_release+0x280/0x280 [ 50.902131] ? chown_common+0x740/0x740 [ 50.906084] ? security_inode_permission+0xd5/0x110 [ 50.911079] ? inode_permission+0xb4/0x570 [ 50.915289] vfs_open+0xa0/0xd0 [ 50.918559] path_openat+0x144f/0x5650 [ 50.922453] ? __lock_is_held+0xb6/0x140 [ 50.926546] ? path_lookupat.isra.0+0xba0/0xba0 [ 50.931196] ? __mutex_init+0x1f6/0x2a0 [ 50.935147] ? __lock_acquire+0x572/0x4a30 [ 50.939357] ? __do_execve_file.isra.0+0x47a/0x2700 [ 50.944361] ? __x64_sys_execve+0x8f/0xc0 [ 50.948508] ? do_syscall_64+0x1a3/0x800 [ 50.952577] do_filp_open+0x26f/0x370 [ 50.956397] ? may_open_dev+0x100/0x100 [ 50.960375] ? prepare_creds+0xa4/0x4e0 [ 50.964333] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.969241] ? add_lock_to_list.isra.0+0x450/0x450 [ 50.974149] ? __do_execve_file.isra.0+0x901/0x2700 [ 50.979144] do_open_execat+0x20e/0x930 [ 50.983098] ? unregister_binfmt+0x2b0/0x2b0 [ 50.987487] ? kasan_check_read+0x11/0x20 [ 50.991616] ? do_raw_spin_trylock+0x270/0x270 [ 50.996192] ? __phys_addr_symbol+0x30/0x70 [ 51.000505] __do_execve_file.isra.0+0x1966/0x2700 [ 51.005413] ? copy_strings_kernel+0x110/0x110 [ 51.009970] ? __sanitizer_cov_trace_const_cmp8+0x18/0x20 [ 51.015485] ? strncpy_from_user+0x3aa/0x4e0 [ 51.019887] ? digsig_verify.cold+0x32/0x32 [ 51.024187] ? kmem_cache_alloc+0x341/0x710 [ 51.028499] ? do_syscall_64+0x8c/0x800 [ 51.032454] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 51.037983] ? getname_flags+0x277/0x5b0 [ 51.042056] ? trace_hardirqs_off_caller+0x300/0x300 [ 51.047146] __x64_sys_execve+0x8f/0xc0 [ 51.051100] do_syscall_64+0x1a3/0x800 [ 51.054973] ? syscall_return_slowpath+0x5f0/0x5f0 [ 51.059900] ? prepare_exit_to_usermode+0x3b0/0x3b0 [ 51.064943] ? __switch_to_asm+0x34/0x70 [ 51.069007] ? trace_hardirqs_off_thunk+0x1a/0x1c [ 51.073830] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 51.079012] RIP: 0033:0x445709 [ 51.082185] 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 [ 51.102280] RSP: 002b:00007f5795ce5d18 EFLAGS: 00000246 ORIG_RAX: 000000000000003b