[....] Starting enhanced syslogd: rsyslogd[ 14.151263] audit: type=1400 audit(1543738549.142:4): avc: denied { syslog } for pid=1921 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[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. Starting mcstransd: [....] Starting file context maintaining daemon: restorecond[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 Warning: Permanently added '10.128.0.71' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 34.879590] [ 34.881253] ====================================================== [ 34.887540] [ INFO: possible circular locking dependency detected ] [ 34.893923] 4.4.166+ #17 Not tainted [ 34.897607] ------------------------------------------------------- [ 34.903984] syz-executor769/2073 is trying to acquire lock: [ 34.909665] (&bdev->bd_mutex){+.+.+.}, at: [] blkdev_reread_part+0x1e/0x40 [ 34.918792] [ 34.918792] but task is already holding lock: [ 34.924738] (&lo->lo_ctl_mutex#2){+.+...}, at: [] lo_compat_ioctl+0x103/0x140 [ 34.934278] [ 34.934278] which lock already depends on the new lock. [ 34.934278] [ 34.942566] [ 34.942566] the existing dependency chain (in reverse order) is: [ 34.950160] -> #2 (&lo->lo_ctl_mutex#2){+.+...}: [ 34.955668] [] lock_acquire+0x15e/0x450 [ 34.961914] [] mutex_lock_nested+0xc2/0xb60 [ 34.968502] [] lo_release+0x85/0x1a0 [ 34.974480] [] __blkdev_put+0x636/0x840 [ 34.980725] [] blkdev_put+0x85/0x560 [ 34.986706] [] blkdev_close+0x8b/0xb0 [ 34.992824] [] __fput+0x235/0x6f0 [ 34.998555] [] ____fput+0x15/0x20 [ 35.004277] [] task_work_run+0x21c/0x2d0 [ 35.010609] [] exit_to_usermode_loop+0x13d/0x160 [ 35.017645] [] syscall_return_slowpath+0x254/0x2d0 [ 35.024856] [] int_ret_from_sys_call+0x25/0xa3 [ 35.031712] -> #1 (loop_index_mutex){+.+.+.}: [ 35.036845] [] lock_acquire+0x15e/0x450 [ 35.043087] [] mutex_lock_nested+0xc2/0xb60 [ 35.049725] [] lo_open+0x1b/0xa0 [ 35.055367] [] __blkdev_get+0x2ae/0xdf0 [ 35.061626] [] blkdev_get+0x2da/0x920 [ 35.067691] [] blkdev_open+0x1a5/0x250 [ 35.073841] [] do_dentry_open+0x38d/0xbd0 [ 35.080255] [] vfs_open+0x12a/0x210 [ 35.086142] [] path_openat+0xc10/0x3f10 [ 35.092381] [] do_filp_open+0x197/0x270 [ 35.098623] [] do_sys_open+0x31c/0x610 [ 35.104781] [] SyS_open+0x2d/0x40 [ 35.110504] [] entry_SYSCALL_64_fastpath+0x1e/0x9a [ 35.117699] -> #0 (&bdev->bd_mutex){+.+.+.}: [ 35.122734] [] __lock_acquire+0x3cd4/0x5530 [ 35.129324] [] lock_acquire+0x15e/0x450 [ 35.135562] [] mutex_lock_nested+0xc2/0xb60 [ 35.142147] [] blkdev_reread_part+0x1e/0x40 [ 35.148750] [] loop_reread_partitions+0x7c/0x90 [ 35.155694] [] loop_set_status+0xa7e/0xfe0 [ 35.162194] [] loop_set_status_compat+0x9a/0xf0 [ 35.169127] [] lo_compat_ioctl+0x10e/0x140 [ 35.175661] [] compat_blkdev_ioctl+0x3a4/0x3546 [ 35.182600] [] compat_SyS_ioctl+0x4af/0x2220 [ 35.189282] [] do_fast_syscall_32+0x31e/0xa80 [ 35.196176] [] sysenter_flags_fixed+0xd/0x1a [ 35.202852] [ 35.202852] other info that might help us debug this: [ 35.202852] [ 35.210968] Chain exists of: &bdev->bd_mutex --> loop_index_mutex --> &lo->lo_ctl_mutex#2 [ 35.220531] Possible unsafe locking scenario: [ 35.220531] [ 35.226565] CPU0 CPU1 [ 35.231214] ---- ---- [ 35.235855] lock(&lo->lo_ctl_mutex#2); [ 35.240265] lock(loop_index_mutex); [ 35.246939] lock(&lo->lo_ctl_mutex#2); [ 35.254013] lock(&bdev->bd_mutex); [ 35.258000] [ 35.258000] *** DEADLOCK *** [ 35.258000] [ 35.264074] 1 lock held by syz-executor769/2073: [ 35.268803] #0: (&lo->lo_ctl_mutex#2){+.+...}, at: [] lo_compat_ioctl+0x103/0x140 [ 35.278951] [ 35.278951] stack backtrace: [ 35.283514] CPU: 0 PID: 2073 Comm: syz-executor769 Not tainted 4.4.166+ #17 [ 35.290587] 0000000000000000 d966f09b8dcbfade ffff8801d41ff5d0 ffffffff81aa62ad [ 35.298595] ffffffff83a9b890 ffffffff83a9acc0 ffff8800b7ad4740 ffffffff83ac0580 [ 35.306610] ffff8800b7ad5028 ffff8801d41ff620 ffffffff813a9549 ffff8800b7ad4740 [ 35.314664] Call Trace: [ 35.317245] [] dump_stack+0xc1/0x124 [ 35.322602] [] print_circular_bug.cold.31+0x2f6/0x435 [ 35.329447] [