syzbot

======================================================
WARNING: possible circular locking dependency detected
5.6.0-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.5/10846 is trying to acquire lock:
ffff88809eb8f7f8 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: lock_trace fs/proc/base.c:408 [inline]
ffff88809eb8f7f8 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: proc_pid_stack+0xd8/0x200 fs/proc/base.c:452

but task is already holding lock:
ffff8880a96896d8 (&p->lock){+.+.}-{3:3}, at: seq_read+0x66/0xd20 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}:
       lock_acquire+0x169/0x480 kernel/locking/lockdep.c:4923
       __mutex_lock_common+0x189/0x2fc0 kernel/locking/mutex.c:956
       __mutex_lock kernel/locking/mutex.c:1103 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1118
       seq_read+0x66/0xd20 fs/seq_file.c:161
       proc_reg_read+0x1cd/0x2c0 fs/proc/inode.c:223
       do_loop_readv_writev fs/read_write.c:714 [inline]
       do_iter_read+0x43e/0x550 fs/read_write.c:935
       vfs_readv+0xc2/0x120 fs/read_write.c:1053
       kernel_readv fs/splice.c:365 [inline]
       default_file_splice_read+0x579/0xa40 fs/splice.c:422
       do_splice_to fs/splice.c:892 [inline]
       splice_direct_to_actor+0x3c1/0xb40 fs/splice.c:971
       do_splice_direct+0x201/0x340 fs/splice.c:1080
       do_sendfile+0x809/0xfd0 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+0x164/0x1a0 fs/read_write.c:1567
       do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
       entry_SYSCALL_64_after_hwframe+0x49/0xb3

-> #2 (sb_writers#3){.+.+}-{0:0}:
       lock_acquire+0x169/0x480 kernel/locking/lockdep.c:4923
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write+0x14b/0x410 fs/super.c:1674
       sb_start_write include/linux/fs.h:1650 [inline]
       mnt_want_write+0x45/0x90 fs/namespace.c:354
       ovl_setattr+0x53/0x740 fs/overlayfs/inode.c:27
       notify_change+0xc14/0x1050 fs/attr.c:336
       utimes_common+0x3fc/0x680 fs/utimes.c:60
       do_utimes+0x23b/0x2d0 fs/utimes.c:125
       do_futimesat fs/utimes.c:188 [inline]
       __do_sys_utimes fs/utimes.c:201 [inline]
       __se_sys_utimes fs/utimes.c:198 [inline]
       __x64_sys_utimes+0xd4/0x250 fs/utimes.c:198
       do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
       entry_SYSCALL_64_after_hwframe+0x49/0xb3

-> #1 (&ovl_i_mutex_dir_key[depth]#2){++++}-{3:3}:
       lock_acquire+0x169/0x480 kernel/locking/lockdep.c:4923
       down_read+0x36/0x50 kernel/locking/rwsem.c:1492
       inode_lock_shared include/linux/fs.h:802 [inline]
       do_last fs/namei.c:3400 [inline]
       path_openat+0xbf2/0x40f0 fs/namei.c:3607
       do_filp_open+0x191/0x3a0 fs/namei.c:3637
       do_open_execat+0x101/0x5f0 fs/exec.c:860
       __do_execve_file+0x6ea/0x1b80 fs/exec.c:1791
       do_execveat_common fs/exec.c:1897 [inline]
       do_execveat fs/exec.c:1925 [inline]
       __do_sys_execveat fs/exec.c:2001 [inline]
       __se_sys_execveat fs/exec.c:1993 [inline]
       __x64_sys_execveat+0xcf/0xe0 fs/exec.c:1993
       do_syscall_64+0xf3/0x1b0 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+0x1b09/0x8920 kernel/locking/lockdep.c:3237
       __lock_acquire+0x116c/0x2b90 kernel/locking/lockdep.c:4344
       lock_acquire+0x169/0x480 kernel/locking/lockdep.c:4923
       __mutex_lock_common+0x189/0x2fc0 kernel/locking/mutex.c:956
       __mutex_lock kernel/locking/mutex.c:1103 [inline]
       mutex_lock_killable_nested+0x1a/0x20 kernel/locking/mutex.c:1133
       lock_trace fs/proc/base.c:408 [inline]
       proc_pid_stack+0xd8/0x200 fs/proc/base.c:452
       proc_single_show+0xd5/0x160 fs/proc/base.c:758
       seq_read+0x4aa/0xd20 fs/seq_file.c:229
       __vfs_read+0xa7/0x700 fs/read_write.c:425
       vfs_read+0x1c3/0x400 fs/read_write.c:461
       ksys_read+0x11b/0x220 fs/read_write.c:587
       do_syscall_64+0xf3/0x1b0 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 ***

2 locks held by syz-executor.5/10846:
 #0: ffff88808b19b430 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x25d/0x2f0 fs/file.c:826
 #1: ffff8880a96896d8 (&p->lock){+.+.}-{3:3}, at: seq_read+0x66/0xd20 fs/seq_file.c:161

stack backtrace:
CPU: 0 PID: 10846 Comm: syz-executor.5 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+0x1e9/0x30e lib/dump_stack.c:118
 print_circular_bug+0xc72/0xea0 kernel/locking/lockdep.c:1722
 check_noncircular+0x1fb/0x3a0 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+0x1b09/0x8920 kernel/locking/lockdep.c:3237
 __lock_acquire+0x116c/0x2b90 kernel/locking/lockdep.c:4344
 lock_acquire+0x169/0x480 kernel/locking/lockdep.c:4923
 __mutex_lock_common+0x189/0x2fc0 kernel/locking/mutex.c:956
 __mutex_lock kernel/locking/mutex.c:1103 [inline]
 mutex_lock_killable_nested+0x1a/0x20 kernel/locking/mutex.c:1133
 lock_trace fs/proc/base.c:408 [inline]
 proc_pid_stack+0xd8/0x200 fs/proc/base.c:452
 proc_single_show+0xd5/0x160 fs/proc/base.c:758
 seq_read+0x4aa/0xd20 fs/seq_file.c:229
 __vfs_read+0xa7/0x700 fs/read_write.c:425
 vfs_read+0x1c3/0x400 fs/read_write.c:461
 ksys_read+0x11b/0x220 fs/read_write.c:587
 do_syscall_64+0xf3/0x1b0 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:00007fe49e68ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fe49e68b6d4 RCX: 000000000045c849
RDX: 00000000000000b4 RSI: 0000000020000100 RDI: 0000000000000004
RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000877 R14: 00000000004cb2f0 R15: 000000000076bf0c