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SubjectRe: possible deadlock in path_openat
From
syzbot has found a reproducer for the following crash on:

HEAD commit: 6d906f99 Merge tag 'arm64-fixes' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10917b8f200000
kernel config: https://syzkaller.appspot.com/x/.config?x=856fc6d0fbbeede9
dashboard link: https://syzkaller.appspot.com/bug?extid=a55ccfc8a853d3cff213
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101767b7200000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13c15013200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a55ccfc8a853d3cff213@syzkaller.appspotmail.com

overlayfs: workdir and upperdir must reside under the same mount
======================================================
WARNING: possible circular locking dependency detected
5.1.0-rc5+ #74 Not tainted
------------------------------------------------------
syz-executor949/9348 is trying to acquire lock:
000000005d993096 (&ovl_i_mutex_dir_key[depth]#2){++++}, at:
inode_lock_shared include/linux/fs.h:782 [inline]
000000005d993096 (&ovl_i_mutex_dir_key[depth]#2){++++}, at: do_last
fs/namei.c:3321 [inline]
000000005d993096 (&ovl_i_mutex_dir_key[depth]#2){++++}, at:
path_openat+0x1e98/0x46e0 fs/namei.c:3533

but task is already holding lock:
00000000ef248b1d (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds
fs/exec.c:1407 [inline]
00000000ef248b1d (&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:

-> #4 (&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_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102
do_io_accounting+0x1f4/0x830 fs/proc/base.c:2740
proc_tgid_io_accounting+0x23/0x30 fs/proc/base.c:2789
proc_single_show+0xf6/0x170 fs/proc/base.c:744
seq_read+0x4db/0x1130 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+0x4a9/0x660 fs/read_write.c:922
vfs_readv+0xf0/0x160 fs/read_write.c:984
kernel_readv fs/splice.c:358 [inline]
default_file_splice_read+0x475/0x890 fs/splice.c:413
do_splice_to+0x12a/0x190 fs/splice.c:876
splice_direct_to_actor+0x2d2/0x970 fs/splice.c:953
do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
do_sendfile+0x597/0xd00 fs/read_write.c:1443
__do_sys_sendfile64 fs/read_write.c:1504 [inline]
__se_sys_sendfile64 fs/read_write.c:1490 [inline]
__x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1490
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #3 (&p->lock){+.+.}:
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
seq_read+0x71/0x1130 fs/seq_file.c:161
proc_reg_read+0x1fe/0x2c0 fs/proc/inode.c:227
do_loop_readv_writev fs/read_write.c:701 [inline]
do_loop_readv_writev fs/read_write.c:688 [inline]
do_iter_read+0x4a9/0x660 fs/read_write.c:922
vfs_readv+0xf0/0x160 fs/read_write.c:984
kernel_readv fs/splice.c:358 [inline]
default_file_splice_read+0x475/0x890 fs/splice.c:413
do_splice_to+0x12a/0x190 fs/splice.c:876
do_splice+0x110b/0x1420 fs/splice.c:1183
__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

-> #2 (&pipe->mutex/1){+.+.}:
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_nested fs/pipe.c:62 [inline]
pipe_lock+0x6e/0x80 fs/pipe.c:70
iter_file_splice_write+0x18b/0xbe0 fs/splice.c:696
do_splice_from fs/splice.c:847 [inline]
do_splice+0x70a/0x1420 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

-> #1 (sb_writers#6){.+.+}:
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
percpu_down_read include/linux/percpu-rwsem.h:36 [inline]
__sb_start_write+0x20b/0x360 fs/super.c:1613
sb_start_write include/linux/fs.h:1621 [inline]
mnt_want_write+0x3f/0xc0 fs/namespace.c:358
ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24
ovl_do_remove+0xe9/0xd70 fs/overlayfs/dir.c:840
ovl_rmdir+0x1b/0x20 fs/overlayfs/dir.c:890
vfs_rmdir fs/namei.c:3878 [inline]
vfs_rmdir+0x19c/0x470 fs/namei.c:3857
do_rmdir+0x39e/0x420 fs/namei.c:3939
__do_sys_rmdir fs/namei.c:3957 [inline]
__se_sys_rmdir fs/namei.c:3955 [inline]
__x64_sys_rmdir+0x36/0x40 fs/namei.c:3955
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&ovl_i_mutex_dir_key[depth]#2){++++}:
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
down_read+0x3b/0x90 kernel/locking/rwsem.c:24
inode_lock_shared include/linux/fs.h:782 [inline]
do_last fs/namei.c:3321 [inline]
path_openat+0x1e98/0x46e0 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:

Chain exists of:
&ovl_i_mutex_dir_key[depth]#2 --> &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]#2);

*** DEADLOCK ***

1 lock held by syz-executor949/9348:
#0: 00000000ef248b1d (&sig->cred_guard_mutex){+.+.}, at:
prepare_bprm_creds fs/exec.c:1407 [inline]
#0: 00000000ef248b1d (&sig->cred_guard_mutex){+.+.}, at:
__do_execve_file.isra.0+0x376/0x23f0 fs/exec.c:1750

stack backtrace:
CPU: 1 PID: 9348 Comm: syz-executor949 Not tainted 5.1.0-rc5+ #74
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
down_read+0x3b/0x90 kernel/locking/rwsem.c:24
inode_lock_shared include/linux/fs.h:782 [inline]
do_last fs/namei.c:3321 [inline]
path_openat+0x1e98/0x46e0 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: 0033:0x447169
Code: e8 4c bb 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 bb 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fe4c6a6bdb8 EFLAGS: 00000246 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 00000000006dcc68 RCX: 0000000000447169
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000000
RBP: 00000000006dcc60 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc6c
R13: 00007ffd5a5cb62f R14: 00007fe4c6a6c9c0 R15: 0000000000000000

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