KASAN: stack-out-of-bounds Read in __d_lookup

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: cddaf02bcb73 tg3: optionally use eth_platform_get_mac_addr..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1028be2b400000
kernel config: https://syzkaller.appspot.com/x/.config?x=d86f24333880b605
dashboard link: https://syzkaller.appspot.com/bug?extid=26ced08d1e81ff6dd505
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+26ced0...@syzkaller.appspotmail.com

==================================================================
kasan: CONFIG_KASAN_INLINE enabled
BUG: KASAN: stack-out-of-bounds in __d_lookup+0x8bb/0x9e0 fs/dcache.c:2269
kasan: GPF could be caused by NULL-ptr deref or user memory access
Read of size 4 at addr ffff8881dabb87e8 by task syz-executor5/6136
general protection fault: 0000 [#1] PREEMPT SMP KASAN

CPU: 0 PID: 16757 Comm: syz-executor3 Not tainted 4.20.0-rc2+ #302
CPU: 1 PID: 6136 Comm: syz-executor5 Not tainted 4.20.0-rc2+ #302
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:lookup_object lib/debugobjects.c:157 [inline]
RIP: 0010:debug_object_deactivate+0x191/0x450 lib/debugobjects.c:543
Call Trace:
------------[ cut here ]------------
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
Bad or missing usercopy whitelist? Kernel memory overwrite attempt detected
to SLAB object '$' (offset 18446744071926971184, size 64)!
WARNING: CPU: 0 PID: 16757 at mm/usercopy.c:83 usercopy_warn+0xee/0x110
mm/usercopy.c:78
Kernel panic - not syncing: panic_on_warn set ...
print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
__d_lookup+0x8bb/0x9e0 fs/dcache.c:2269
d_lookup+0x1e0/0x300 fs/dcache.c:2214
mountpoint_last fs/namei.c:2657 [inline]
path_mountpoint+0x1f1/0x2180 fs/namei.c:2695
filename_mountpoint+0x245/0x460 fs/namei.c:2717
user_path_mountpoint_at+0x37/0x40 fs/namei.c:2747
ksys_umount+0x1c5/0x12d0 fs/namespace.c:1645
__do_sys_umount fs/namespace.c:1671 [inline]
__se_sys_umount fs/namespace.c:1669 [inline]
__x64_sys_umount+0x54/0x80 fs/namespace.c:1669
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459fb7
Code: 44 00 00 b8 08 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 9d 89 fb ff c3
66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 7d 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff85e4efe8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 0000000000043083 RCX: 0000000000459fb7
RDX: 000000000000000c RSI: 0000000000000002 RDI: 00007fff85e50120
RBP: 00000000000004eb R08: 0000000000000001 R09: 0000000002590940
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff85e50120
R13: 0000000000043016 R14: 0000000000000000 R15: 0000000000000005

The buggy address belongs to the page:
page:ffffea00076aee00 count:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 dead000000000100 dead000000000200 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881dabb8680: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
ffff8881dabb8700: f1 00 f2 f2 f2 f2 f2 f2 f2 f8 f2 f2 f2 00 00 00
> ffff8881dabb8780: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
^
ffff8881dabb8800: f1 f8 f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00
ffff8881dabb8880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================
Kernel Offset: disabled

======================================================
WARNING: possible circular locking dependency detected
4.20.0-rc2+ #302 Not tainted
------------------------------------------------------
syz-executor3/16757 is trying to acquire lock:
00000000862a567e ((console_sem).lock){-.-.}, at: down_trylock+0x13/0x70
kernel/locking/semaphore.c:136

but task is already holding lock:
00000000e8d8e78f (&obj_hash[i].lock){-.-.}, at:
debug_object_deactivate+0xf7/0x450 lib/debugobjects.c:541

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&obj_hash[i].lock){-.-.}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
__debug_object_init+0x127/0x1290 lib/debugobjects.c:384
debug_object_init+0x16/0x20 lib/debugobjects.c:432
debug_hrtimer_init kernel/time/hrtimer.c:410 [inline]
debug_init kernel/time/hrtimer.c:458 [inline]
hrtimer_init+0x97/0x490 kernel/time/hrtimer.c:1308
init_dl_task_timer+0x1b/0x50 kernel/sched/deadline.c:1057
__sched_fork+0x2ae/0x590 kernel/sched/core.c:2166
init_idle+0x75/0x740 kernel/sched/core.c:5374
sched_init+0xb33/0xc07 kernel/sched/core.c:6060
start_kernel+0x4be/0xa2b init/main.c:608
x86_64_start_reservations+0x2e/0x30 arch/x86/kernel/head64.c:472
x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:451
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

-> #2 (&rq->lock){-.-.}:
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
rq_lock kernel/sched/sched.h:1126 [inline]
task_fork_fair+0xb0/0x6d0 kernel/sched/fair.c:9768
sched_fork+0x443/0xba0 kernel/sched/core.c:2359
copy_process+0x25b8/0x87a0 kernel/fork.c:1887
_do_fork+0x1cb/0x11d0 kernel/fork.c:2216
kernel_thread+0x34/0x40 kernel/fork.c:2275
rest_init+0x28/0x372 init/main.c:409
arch_call_rest_init+0xe/0x1b
start_kernel+0x9f0/0xa2b init/main.c:745
x86_64_start_reservations+0x2e/0x30 arch/x86/kernel/head64.c:472
x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:451
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

-> #1 (&p->pi_lock){-.-.}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
try_to_wake_up+0xdc/0x1490 kernel/sched/core.c:1965
wake_up_process+0x10/0x20 kernel/sched/core.c:2129
__up.isra.1+0x1c0/0x2a0 kernel/locking/semaphore.c:262
up+0x13c/0x1c0 kernel/locking/semaphore.c:187
__up_console_sem+0xbe/0x1b0 kernel/printk/printk.c:236
console_unlock+0x811/0x1190 kernel/printk/printk.c:2432
vprintk_emit+0x391/0x990 kernel/printk/printk.c:1922
vprintk_default+0x28/0x30 kernel/printk/printk.c:1964
vprintk_func+0x7e/0x181 kernel/printk/printk_safe.c:398
printk+0xa7/0xcf kernel/printk/printk.c:1997
check_stack_usage kernel/exit.c:755 [inline]
do_exit.cold.18+0x57/0x16f kernel/exit.c:916
do_group_exit+0x177/0x440 kernel/exit.c:970
__do_sys_exit_group kernel/exit.c:981 [inline]
__se_sys_exit_group kernel/exit.c:979 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:979
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 ((console_sem).lock){-.-.}:

other info that might help us debug this:

Chain exists of:
(console_sem).lock --> &rq->lock --> &obj_hash[i].lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&obj_hash[i].lock);
lock(&rq->lock);
lock(&obj_hash[i].lock);
lock((console_sem).lock);

*** DEADLOCK ***

5 locks held by syz-executor3/16757:
#0: 00000000c302e0be (rcu_read_lock){....}, at: __skb_unlink
include/linux/skbuff.h:1901 [inline]
#0: 00000000c302e0be (rcu_read_lock){....}, at: __skb_dequeue
include/linux/skbuff.h:1917 [inline]
#0: 00000000c302e0be (rcu_read_lock){....}, at:
process_backlog+0x1dd/0x7a0 net/core/dev.c:5862
#1: 00000000c302e0be (rcu_read_lock){....}, at: __skb_pull
include/linux/skbuff.h:2134 [inline]
#1: 00000000c302e0be (rcu_read_lock){....}, at:
ip_local_deliver_finish+0x13d/0x390 net/ipv4/ip_input.c:231
#2: 00000000f5418890 (hrtimer_bases.lock){-.-.}, at:
hrtimer_interrupt+0xfc/0x780 kernel/time/hrtimer.c:1499
#3: 00000000e8d8e78f (&obj_hash[i].lock){-.-.}, at:
debug_object_deactivate+0xf7/0x450 lib/debugobjects.c:541
#4: 00000000c302e0be (rcu_read_lock){....}, at:
atomic_notifier_call_chain+0x0/0x190 kernel/notifier.c:329

stack backtrace:
CPU: 0 PID: 16757 Comm: syz-executor3 Not tainted 4.20.0-rc2+ #302
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.