======================================================
WARNING: possible circular locking dependency detected
5.1.0-rc1+ #33 Not tainted
------------------------------------------------------
syz-executor850/7765 is trying to acquire lock:
00000000d6dfb9eb (&pipe->mutex/1){+.+.}, at: __pipe_lock fs/pipe.c:83 [inline]
00000000d6dfb9eb (&pipe->mutex/1){+.+.}, at: fifo_open+0x159/0xb00 fs/pipe.c:930

but task is already holding lock:
00000000f27e5005 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline]
00000000f27e5005 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x376/0x23f0 fs/exec.c:1750

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
       mutex_lock_interruptible_nested+0x16/0x20 kernel/locking/mutex.c:1109
       proc_pid_attr_write+0x200/0x580 fs/proc/base.c:2558
       __vfs_write+0x8d/0x110 fs/read_write.c:485
       __kernel_write+0x110/0x3b0 fs/read_write.c:506
       write_pipe_buf+0x15d/0x1f0 fs/splice.c:793
       splice_from_pipe_feed fs/splice.c:499 [inline]
       __splice_from_pipe+0x395/0x7d0 fs/splice.c:623
       splice_from_pipe+0x108/0x170 fs/splice.c:658
       default_file_splice_write+0x3c/0x90 fs/splice.c:805
       do_splice_from fs/splice.c:847 [inline]
       do_splice+0x70a/0x13c0 fs/splice.c:1154
       __do_sys_splice fs/splice.c:1424 [inline]
       __se_sys_splice fs/splice.c:1404 [inline]
       __x64_sys_splice+0x2c6/0x330 fs/splice.c:1404
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&pipe->mutex/1){+.+.}:
       check_prevs_add kernel/locking/lockdep.c:2333 [inline]
       validate_chain kernel/locking/lockdep.c:2714 [inline]
       __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
       __pipe_lock fs/pipe.c:83 [inline]
       fifo_open+0x159/0xb00 fs/pipe.c:930
       do_dentry_open+0x488/0x1160 fs/open.c:771
       vfs_open+0xa0/0xd0 fs/open.c:880
       do_last fs/namei.c:3416 [inline]
       path_openat+0x10e9/0x46e0 fs/namei.c:3533
       do_filp_open+0x1a1/0x280 fs/namei.c:3563
       do_open_execat+0x137/0x690 fs/exec.c:856
       __do_execve_file.isra.0+0x178d/0x23f0 fs/exec.c:1758
       do_execveat_common fs/exec.c:1865 [inline]
       do_execve fs/exec.c:1882 [inline]
       __do_sys_execve fs/exec.c:1958 [inline]
       __se_sys_execve fs/exec.c:1953 [inline]
       __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sig->cred_guard_mutex);
                               lock(&pipe->mutex/1);
                               lock(&sig->cred_guard_mutex);
  lock(&pipe->mutex/1);

 *** DEADLOCK ***

1 lock held by syz-executor850/7765:
 #0: 00000000f27e5005 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1407 [inline]
 #0: 00000000f27e5005 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file.isra.0+0x376/0x23f0 fs/exec.c:1750

stack backtrace:
CPU: 1 PID: 7765 Comm: syz-executor850 Not tainted 5.1.0-rc1+ #33
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+0x172/0x1f0 lib/dump_stack.c:113
 print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1571
 check_prev_add.constprop.0+0xf11/0x23c0 kernel/locking/lockdep.c:2220
 check_prevs_add kernel/locking/lockdep.c:2333 [inline]
 validate_chain kernel/locking/lockdep.c:2714 [inline]
 __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
 __mutex_lock_common kernel/locking/mutex.c:925 [inline]
 __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
 __pipe_lock fs/pipe.c:83 [inline]
 fifo_open+0x159/0xb00 fs/pipe.c:930
 do_dentry_open+0x488/0x1160 fs/open.c:771
 vfs_open+0xa0/0xd0 fs/open.c:880
 do_last fs/namei.c:3416 [inline]
 path_openat+0x10e9/0x46e0 fs/namei.c:3533
 do_filp_open+0x1a1/0x280 fs/namei.c:3563
 do_open_execat+0x137/0x690 fs/exec.c:856
 __do_execve_file.isra.0+0x178d/0x23f0 fs/exec.c:1758
 do_execveat_common fs/exec.c:1865 [inline]
 do_execve fs/exec.c:1882 [inline]
 __do_sys_execve fs/exec.c:1958 [inline]
 __se_sys_execve fs/exec.c:1953 [inline]
 __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4402a9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff212954a8 EFLAGS: 00000246 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004402a9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000480
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401b30
R13: 0000000000401bc0 R14: 0000000000000000 R15: 0000000000000000