syzbot

overlayfs: './bus' not a directory
overlayfs: './bus' not a directory
overlayfs: './bus' not a directory
overlayfs: './bus' not a directory
======================================================
WARNING: possible circular locking dependency detected
4.19.197-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.2/14753 is trying to acquire lock:
overlayfs: './bus' not a directory
00000000e101582f (&ovl_i_mutex_dir_key[depth]){++++}, at: inode_lock_shared include/linux/fs.h:758 [inline]
00000000e101582f (&ovl_i_mutex_dir_key[depth]){++++}, at: lookup_slow fs/namei.c:1688 [inline]
00000000e101582f (&ovl_i_mutex_dir_key[depth]){++++}, at: walk_component+0x798/0xda0 fs/namei.c:1811

but task is already holding lock:
000000007288cee2 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1419 [inline]
000000007288cee2 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file+0x38c/0x2360 fs/exec.c:1762

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&sig->cred_guard_mutex){+.+.}:
       lock_trace fs/proc/base.c:402 [inline]
       proc_pid_stack+0x160/0x350 fs/proc/base.c:452
       proc_single_show+0xeb/0x170 fs/proc/base.c:755
       seq_read+0x4be/0x1160 fs/seq_file.c:229
       do_loop_readv_writev fs/read_write.c:701 [inline]
       do_loop_readv_writev fs/read_write.c:688 [inline]
       do_iter_read+0x471/0x630 fs/read_write.c:925
       vfs_readv+0xe5/0x150 fs/read_write.c:987
       do_preadv fs/read_write.c:1071 [inline]
       __do_sys_preadv fs/read_write.c:1121 [inline]
       __se_sys_preadv fs/read_write.c:1116 [inline]
       __x64_sys_preadv+0x22b/0x310 fs/read_write.c:1116
       do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&p->lock){+.+.}:
       seq_read+0x6b/0x1160 fs/seq_file.c:161
       proc_reg_read+0x1bd/0x2d0 fs/proc/inode.c:231
       do_loop_readv_writev fs/read_write.c:701 [inline]
       do_loop_readv_writev fs/read_write.c:688 [inline]
       do_iter_read+0x471/0x630 fs/read_write.c:925
       vfs_readv+0xe5/0x150 fs/read_write.c:987
       kernel_readv fs/splice.c:362 [inline]
       default_file_splice_read+0x457/0xa00 fs/splice.c:417
       do_splice_to+0x10e/0x160 fs/splice.c:881
       splice_direct_to_actor+0x2b9/0x8d0 fs/splice.c:959
       do_splice_direct+0x1a7/0x270 fs/splice.c:1068
       do_sendfile+0x550/0xc30 fs/read_write.c:1447
       __do_sys_sendfile64 fs/read_write.c:1508 [inline]
       __se_sys_sendfile64+0x147/0x160 fs/read_write.c:1494
       do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (sb_writers#3){.+.+}:
       sb_start_write include/linux/fs.h:1579 [inline]
       mnt_want_write+0x3a/0xb0 fs/namespace.c:360
       ovl_create_object+0x96/0x290 fs/overlayfs/dir.c:600
       lookup_open+0x893/0x1a20 fs/namei.c:3235
       do_last fs/namei.c:3327 [inline]
       path_openat+0x1094/0x2df0 fs/namei.c:3537
       do_filp_open+0x18c/0x3f0 fs/namei.c:3567
       do_sys_open+0x3b3/0x520 fs/open.c:1085
       do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&ovl_i_mutex_dir_key[depth]){++++}:
       down_read+0x36/0x80 kernel/locking/rwsem.c:24
       inode_lock_shared include/linux/fs.h:758 [inline]
       lookup_slow fs/namei.c:1688 [inline]
       walk_component+0x798/0xda0 fs/namei.c:1811
       link_path_walk.part.0+0x901/0x1230 fs/namei.c:2142
       link_path_walk fs/namei.c:2073 [inline]
       path_openat+0x1db/0x2df0 fs/namei.c:3536
       do_filp_open+0x18c/0x3f0 fs/namei.c:3567
       do_open_execat+0x11d/0x5b0 fs/exec.c:853
       __do_execve_file+0x1a8b/0x2360 fs/exec.c:1770
       do_execveat_common fs/exec.c:1879 [inline]
       do_execve+0x35/0x50 fs/exec.c:1896
       __do_sys_execve fs/exec.c:1977 [inline]
       __se_sys_execve fs/exec.c:1972 [inline]
       __x64_sys_execve+0x7c/0xa0 fs/exec.c:1972
       do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
  &ovl_i_mutex_dir_key[depth] --> &p->lock --> &sig->cred_guard_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sig->cred_guard_mutex);
                               lock(&p->lock);
                               lock(&sig->cred_guard_mutex);
  lock(&ovl_i_mutex_dir_key[depth]);

 *** DEADLOCK ***

1 lock held by syz-executor.2/14753:
 #0: 000000007288cee2 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds fs/exec.c:1419 [inline]
 #0: 000000007288cee2 (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file+0x38c/0x2360 fs/exec.c:1762

stack backtrace:
CPU: 0 PID: 14753 Comm: syz-executor.2 Not tainted 4.19.197-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+0x1fc/0x2ef lib/dump_stack.c:118
 print_circular_bug.constprop.0.cold+0x2d7/0x41e kernel/locking/lockdep.c:1222
 check_prev_add kernel/locking/lockdep.c:1866 [inline]
 check_prevs_add kernel/locking/lockdep.c:1979 [inline]
 validate_chain kernel/locking/lockdep.c:2420 [inline]
 __lock_acquire+0x30c9/0x3ff0 kernel/locking/lockdep.c:3416
 lock_acquire+0x170/0x3c0 kernel/locking/lockdep.c:3908
 down_read+0x36/0x80 kernel/locking/rwsem.c:24
 inode_lock_shared include/linux/fs.h:758 [inline]
 lookup_slow fs/namei.c:1688 [inline]
 walk_component+0x798/0xda0 fs/namei.c:1811
 link_path_walk.part.0+0x901/0x1230 fs/namei.c:2142
 link_path_walk fs/namei.c:2073 [inline]
 path_openat+0x1db/0x2df0 fs/namei.c:3536
 do_filp_open+0x18c/0x3f0 fs/namei.c:3567
 do_open_execat+0x11d/0x5b0 fs/exec.c:853
 __do_execve_file+0x1a8b/0x2360 fs/exec.c:1770
 do_execveat_common fs/exec.c:1879 [inline]
 do_execve+0x35/0x50 fs/exec.c:1896
 __do_sys_execve fs/exec.c:1977 [inline]
 __se_sys_execve fs/exec.c:1972 [inline]
 __x64_sys_execve+0x7c/0xa0 fs/exec.c:1972
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4e4858d188 EFLAGS: 00000246 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9
RDX: 0000000020000f40 RSI: 0000000020000d80 RDI: 0000000020000780
RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
R13: 00007ffce1049c1f R14: 00007f4e4858d300 R15: 0000000000022000
overlayfs: './bus' not a directory
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