[....] Starting enhanced syslogd: rsyslogd[ 10.224283] audit: type=1400 audit(1514737450.245:4): avc: denied { syslog } for pid=3175 comm="rsyslogd" capability=34 scontext=system_u:system_r:kernel_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclass=capability2 permissive=1 [?25l[?1c7[ ok 8[?25h[?0c. [....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. Starting mcstransd: [....] Starting file context maintaining daemon: restorecond[?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 '10.128.0.30' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 19.952255] [ 19.952576] ====================================================== [ 19.953404] [ INFO: possible circular locking dependency detected ] [ 19.954245] 4.9.73-gf3f3457 #11 Not tainted [ 19.954817] ------------------------------------------------------- [ 19.955666] syzkaller620827/3324 is trying to acquire lock: [ 19.956416] (&bdev->bd_mutex){+.+.+.}, at: [] blkdev_reread_part+0x1e/0x40 [ 19.957676] but task is already holding lock: [ 19.958291] (&lo->lo_ctl_mutex#2){+.+...}, at: [] lo_compat_ioctl+0x109/0x140 [ 19.959616] which lock already depends on the new lock. [ 19.959616] [ 19.960539] [ 19.960539] the existing dependency chain (in reverse order) is: [ 19.961533] -> #1 (&lo->lo_ctl_mutex#2){+.+...}: [ 19.962381] lock_acquire+0x12e/0x410 [ 19.962957] mutex_lock_nested+0xbb/0x870 [ 19.963574] lo_release+0x6b/0x140 [ 19.964114] __blkdev_put+0x5f7/0x7e0 [ 19.964686] blkdev_put+0x85/0x550 [ 19.965226] blkdev_close+0x8b/0xb0 [ 19.965799] __fput+0x28c/0x6e0 [ 19.966307] ____fput+0x15/0x20 [ 19.966828] task_work_run+0x115/0x190 [ 19.967412] exit_to_usermode_loop+0xfc/0x120 [ 19.968076] syscall_return_slowpath+0x1a0/0x1e0 [ 19.968787] entry_SYSCALL_64_fastpath+0xc4/0xc6 [ 19.969479] -> #0 (&bdev->bd_mutex){+.+.+.}: [ 19.970230] __lock_acquire+0x2bf9/0x3640 [ 19.970866] lock_acquire+0x12e/0x410 [ 19.971439] mutex_lock_nested+0xbb/0x870 [ 19.972069] blkdev_reread_part+0x1e/0x40 [ 19.974749] loop_reread_partitions+0x78/0xe0 [ 19.979726] loop_set_status+0x995/0xfc0 [ 19.984270] loop_set_status_compat+0x9a/0x100 [ 19.989334] lo_compat_ioctl+0x114/0x140 [ 19.993879] compat_blkdev_ioctl+0x3e3/0x3bc0 [ 19.998859] compat_SyS_ioctl+0x15f/0x2050 [ 20.003585] do_fast_syscall_32+0x2f7/0x890 [ 20.008390] entry_SYSENTER_compat+0x51/0x60 [ 20.013279] [ 20.013279] other info that might help us debug this: [ 20.013279] [ 20.021382] Possible unsafe locking scenario: [ 20.021382] [ 20.027401] CPU0 CPU1 [ 20.032030] ---- ---- [ 20.036658] lock(&lo->lo_ctl_mutex#2); [ 20.041014] lock(&bdev->bd_mutex); [ 20.047429] lock(&lo->lo_ctl_mutex#2); [ 20.054304] lock(&bdev->bd_mutex); [ 20.058198] [ 20.058198] *** DEADLOCK *** [ 20.058198] [ 20.064219] 1 lock held by syzkaller620827/3324: [ 20.068936] #0: (&lo->lo_ctl_mutex#2){+.+...}, at: [] lo_compat_ioctl+0x109/0x140 [ 20.078818] [ 20.078818] stack backtrace: [ 20.083279] CPU: 0 PID: 3324 Comm: syzkaller620827 Not tainted 4.9.73-gf3f3457 #11 [ 20.090949] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 20.100272] ffff8801cee6f768 ffffffff81d922b9 ffffffff8537b610 ffffffff8537b610 [ 20.108213] ffffffff853a7c80 ffff8801cc12d0d8 ffff8801cc12c800 ffff8801cee6f7b0 [ 20.116153] ffffffff812367e1 ffff8801cc12d0d8 00000000cc12d0b0 ffff8801cc12d0d8 [ 20.124100] Call Trace: [ 20.126654] [] dump_stack+0xc1/0x128 [ 20.131988] [] print_circular_bug+0x271/0x310 [ 20.138099] [] __lock_acquire+0x2bf9/0x3640 [ 20.144035] [] ? debug_check_no_locks_freed+0x2c0/0x2c0 [ 20.151010] [] ? __lock_acquire+0x629/0x3640 [ 20.157032] [] ? __lock_is_held+0xa1/0xf0 [ 20.162792] [] lock_acquire+0x12e/0x410 [ 20.168378] [] ? blkdev_reread_part+0x1e/0x40 [ 20.174489] [] ? blkdev_reread_part+0x1e/0x40 [ 20.180599] [] mutex_lock_nested+0xbb/0x870 [ 20.186534] [] ? blkdev_reread_part+0x1e/0x40 [ 20.192642] [] ? mutex_lock_killable_nested+0x960/0x960 [ 20.199623] [] ? __wake_up+0x1e/0x50 [ 20.204950] [] ? _raw_spin_unlock_irqrestore+0x5a/0x70 [ 20.211847] [] ? trace_hardirqs_on_caller+0x38b/0x590 [ 20.218654] [] blkdev_reread_part+0x1e/0x40 [ 20.224589] [] loop_reread_partitions+0x78/0xe0 [ 20.230868] [] loop_set_status+0x995/0xfc0 [ 20.236715] [] loop_set_status_compat+0x9a/0x100 [ 20.243084] [] ? loop_set_status+0xfc0/0xfc0 [ 20.249104] [] lo_compat_ioctl+0x114/0x140 [ 20.254951] [] ? lo_ioctl+0x1990/0x1990 [ 20.260541] [] compat_blkdev_ioctl+0x3e3/0x3bc0 [ 20.266824] [] ? rcu_read_lock_sched_held+0x103/0x120 [ 20.273627] [] ? cfq_dispatch_requests+0x2f40/0x2f40 [ 20.280343] [] ? putname+0xf3/0x130 [ 20.285584] [] ? security_file_ioctl+0x89/0xb0 [ 20.291786] [] compat_SyS_ioctl+0x15f/0x2050 [ 20.297816] [] ? cfq_dispatch_requests+0x2f40/