xfs: fix scrub stats file permissions

When the kernel is in lockdown mode, debugfs will only show files that
are world-readable and cannot be written, mmaped, or used with ioctl.
That more or less describes the scrub stats file, except that the
permissions are wrong -- they should be 0444, not 0644. You can't write
the stats file, so the 0200 makes no sense.

Meanwhile, the clear_stats file is only writable, but it got mode 0400
instead of 0200, which would make more sense.

Fix both files so that they make sense.

Fixes: d7a74cad8f451 ("xfs: track usage statistics of online fsck")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

xfs: teach scrub to check file nlinks

Create the necessary scrub code to walk the filesystem's directory tree
so that we can compute file link counts. Similar to quotacheck, we
create an incore shadow array of link count information and then we walk
the filesystem a second time to compare the link counts. We need live
updates to keep the information up to date during the lengthy scan, so
this scrubber remains disabled until the next patch.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

xfs: implement live quotacheck inode scan

Create a new trio of scrub functions to check quota counters. While the
dquots themselves are filesystem metadata and should be checked early,
the dquot counter values are computed from other metadata and are
therefore summary counters. We don't plug these into the scrub dispatch
just yet, because we still need to be able to watch quota updates while
doing our scan.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

xfs: only call xchk_stats_merge after validating scrub inputs

Harshit Mogalapalli slogged through several reports from our internal
syzbot instance and observed that they all had a common stack trace:

BUG: KASAN: user-memory-access in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: user-memory-access in atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1294 [inline]
BUG: KASAN: user-memory-access in queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
BUG: KASAN: user-memory-access in do_raw_spin_lock include/linux/spinlock.h:187 [inline]
BUG: KASAN: user-memory-access in __raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
BUG: KASAN: user-memory-access in _raw_spin_lock+0x76/0xe0 kernel/locking/spinlock.c:154
Write of size 4 at addr 0000001dd87ee280 by task syz-executor365/1543

CPU: 2 PID: 1543 Comm: syz-executor365 Not tainted 6.5.0-syzk #1
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x83/0xb0 lib/dump_stack.c:106
print_report+0x3f8/0x620 mm/kasan/report.c:478
kasan_report+0xb0/0xe0 mm/kasan/report.c:588
check_region_inline mm/kasan/generic.c:181 [inline]
kasan_check_range+0x139/0x1e0 mm/kasan/generic.c:187
instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1294 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
do_raw_spin_lock include/linux/spinlock.h:187 [inline]
__raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
_raw_spin_lock+0x76/0xe0 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
xchk_stats_merge_one.isra.1+0x39/0x650 fs/xfs/scrub/stats.c:191
xchk_stats_merge+0x5f/0xe0 fs/xfs/scrub/stats.c:225
xfs_scrub_metadata+0x252/0x14e0 fs/xfs/scrub/scrub.c:599
xfs_ioc_scrub_metadata+0xc8/0x160 fs/xfs/xfs_ioctl.c:1646
xfs_file_ioctl+0x3fd/0x1870 fs/xfs/xfs_ioctl.c:1955
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl fs/ioctl.c:857 [inline]
__x64_sys_ioctl+0x199/0x220 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3e/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x6e/0xd8
RIP: 0033:0x7ff155af753d
Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 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 8b 0d 1b 79 2c 00 f7 d8 64 89 01 48
RSP: 002b:00007ffc006e2568 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff155af753d
RDX: 00000000200000c0 RSI: 00000000c040583c RDI: 0000000000000003
RBP: 00000000ffffffff R08: 00000000004010c0 R09: 00000000004010c0
R10: 00000000004010c0 R11: 0000000000000246 R12: 0000000000400cb0
R13: 00007ffc006e2670 R14: 0000000000000000 R15: 0000000000000000
</TASK>

The root cause here is that xchk_stats_merge_one walks off the end of
the xchk_scrub_stats.cs_stats array because it has been fed a garbage
value in sm->sm_type. That occurs because I put the xchk_stats_merge
in the wrong place -- it should have been after the last xchk_teardown
call on our way out of xfs_scrub_metadata because we only call the
teardown function if we called the setup function, and we don't call the
setup functions if the inputs are obviously garbage.

Thanks to Harshit for triaging the bug reports and bringing this to my
attention.

Fixes: d7a74cad8f45 ("xfs: track usage statistics of online fsck")
Reported-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

xfs: track usage statistics of online fsck

Track the usage, outcomes, and run times of the online fsck code, and
report these values via debugfs. The columns in the file are:

* scrubber name

* number of scrub invocations
* clean objects found
* corruptions found
* optimizations found
* cross referencing failures
* inconsistencies found during cross referencing
* incomplete scrubs
* warnings
* number of time scrub had to retry
* cumulative amount of time spent scrubbing (microseconds)

* number of repair inovcations
* successfully repaired objects
* cumuluative amount of time spent repairing (microseconds)

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>