====================================================== WARNING: possible circular locking dependency detected 5.6.0-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.1/2687 is trying to acquire lock: ffff8880a8c90538 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: lock_trace+0x45/0xe0 fs/proc/base.c:408 but task is already holding lock: ffff8880a0319308 (&p->lock){+.+.}-{3:3}, at: seq_read+0x6b/0x1160 fs/seq_file.c:161 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&p->lock){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:956 [inline] __mutex_lock+0x156/0x13c0 kernel/locking/mutex.c:1103 seq_read+0x6b/0x1160 fs/seq_file.c:161 proc_reg_read+0x1c1/0x280 fs/proc/inode.c:223 do_loop_readv_writev fs/read_write.c:714 [inline] do_loop_readv_writev fs/read_write.c:701 [inline] do_iter_read+0x488/0x660 fs/read_write.c:935 vfs_readv+0xf0/0x160 fs/read_write.c:1053 kernel_readv fs/splice.c:365 [inline] default_file_splice_read+0x4fb/0xa20 fs/splice.c:422 do_splice_to+0x114/0x160 fs/splice.c:892 splice_direct_to_actor+0x307/0x980 fs/splice.c:971 do_splice_direct+0x1b4/0x280 fs/splice.c:1080 do_sendfile+0x555/0xc50 fs/read_write.c:1520 __do_sys_sendfile64 fs/read_write.c:1581 [inline] __se_sys_sendfile64 fs/read_write.c:1567 [inline] __x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1567 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 -> #2 (sb_writers#3){.+.+}-{0:0}: percpu_down_read include/linux/percpu-rwsem.h:51 [inline] __sb_start_write+0x230/0x470 fs/super.c:1674 sb_start_write include/linux/fs.h:1650 [inline] mnt_want_write+0x3a/0xb0 fs/namespace.c:354 ovl_setattr+0xdd/0x8b0 fs/overlayfs/inode.c:27 notify_change+0xb6d/0x1060 fs/attr.c:336 chown_common+0x4a9/0x550 fs/open.c:652 do_fchownat+0x126/0x1e0 fs/open.c:682 __do_sys_lchown fs/open.c:707 [inline] __se_sys_lchown fs/open.c:705 [inline] __x64_sys_lchown+0x7a/0xc0 fs/open.c:705 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 -> #1 (&ovl_i_mutex_dir_key[depth]){++++}-{3:3}: down_read+0x96/0x420 kernel/locking/rwsem.c:1492 inode_lock_shared include/linux/fs.h:802 [inline] do_last fs/namei.c:3400 [inline] path_openat+0x1b0e/0x32c0 fs/namei.c:3607 do_filp_open+0x192/0x260 fs/namei.c:3637 do_open_execat+0x122/0x600 fs/exec.c:860 __do_execve_file.isra.0+0x16d5/0x2270 fs/exec.c:1791 do_execveat_common fs/exec.c:1897 [inline] do_execve fs/exec.c:1914 [inline] __do_sys_execve fs/exec.c:1990 [inline] __se_sys_execve fs/exec.c:1985 [inline] __x64_sys_execve+0x8a/0xb0 fs/exec.c:1985 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 -> #0 (&sig->cred_guard_mutex){+.+.}-{3:3}: check_prev_add kernel/locking/lockdep.c:2515 [inline] check_prevs_add kernel/locking/lockdep.c:2620 [inline] validate_chain kernel/locking/lockdep.c:3237 [inline] __lock_acquire+0x2c21/0x4e00 kernel/locking/lockdep.c:4344 lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923 __mutex_lock_common kernel/locking/mutex.c:956 [inline] __mutex_lock+0x156/0x13c0 kernel/locking/mutex.c:1103 lock_trace+0x45/0xe0 fs/proc/base.c:408 proc_pid_stack+0xbd/0x1f0 fs/proc/base.c:452 proc_single_show+0xf7/0x1c0 fs/proc/base.c:758 seq_read+0x4b9/0x1160 fs/seq_file.c:229 do_loop_readv_writev fs/read_write.c:714 [inline] do_loop_readv_writev fs/read_write.c:701 [inline] do_iter_read+0x488/0x660 fs/read_write.c:935 vfs_readv+0xf0/0x160 fs/read_write.c:1053 do_preadv+0x1bc/0x270 fs/read_write.c:1145 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 other info that might help us debug this: Chain exists of: &sig->cred_guard_mutex --> sb_writers#3 --> &p->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&p->lock); lock(sb_writers#3); lock(&p->lock); lock(&sig->cred_guard_mutex); *** DEADLOCK *** 1 lock held by syz-executor.1/2687: #0: ffff8880a0319308 (&p->lock){+.+.}-{3:3}, at: seq_read+0x6b/0x1160 fs/seq_file.c:161 stack backtrace: CPU: 1 PID: 2687 Comm: syz-executor.1 Not tainted 5.6.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x188/0x20d lib/dump_stack.c:118 check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1846 check_prev_add kernel/locking/lockdep.c:2515 [inline] check_prevs_add kernel/locking/lockdep.c:2620 [inline] validate_chain kernel/locking/lockdep.c:3237 [inline] __lock_acquire+0x2c21/0x4e00 kernel/locking/lockdep.c:4344 lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923 __mutex_lock_common kernel/locking/mutex.c:956 [inline] __mutex_lock+0x156/0x13c0 kernel/locking/mutex.c:1103 lock_trace+0x45/0xe0 fs/proc/base.c:408 proc_pid_stack+0xbd/0x1f0 fs/proc/base.c:452 proc_single_show+0xf7/0x1c0 fs/proc/base.c:758 seq_read+0x4b9/0x1160 fs/seq_file.c:229 do_loop_readv_writev fs/read_write.c:714 [inline] do_loop_readv_writev fs/read_write.c:701 [inline] do_iter_read+0x488/0x660 fs/read_write.c:935 vfs_readv+0xf0/0x160 fs/read_write.c:1053 do_preadv+0x1bc/0x270 fs/read_write.c:1145 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 RIP: 0033:0x45c849 Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fee8c986c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000127 RAX: ffffffffffffffda RBX: 00007fee8c9876d4 RCX: 000000000045c849 RDX: 00000000000003da RSI: 00000000200017c0 RDI: 0000000000000003 RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 000000000000085a R14: 00000000004cb1ac R15: 000000000076bf0c