Re: [LKP] [locks] dee160df82: BUG:KASAN:null-ptr-deref_in_l

From: NeilBrown
Date: Wed Nov 07 2018 - 20:10:12 EST

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In reply to: Jeff Layton: "Re: [LKP] [locks] dee160df82: BUG:KASAN:null-ptr-deref_in_l"
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On Wed, Nov 07 2018, Jeff Layton wrote:

> On Wed, 2018-11-07 at 16:54 +0100, Thierry Reding wrote:
>> On Wed, Nov 07, 2018 at 07:01:29AM -0500, Jeff Layton wrote:
>> > On Wed, 2018-11-07 at 16:43 +0800, kernel test robot wrote:
>> > > FYI, we noticed the following commit (built with gcc-7):
>> > >
>> > > commit: dee160df820de41ff2f59a715643680822a0ab06 ("locks: use properly initialized file_lock when unlocking.")
>> > > https://git.kernel.org/cgit/linux/kernel/git/jlayton/linux.git locks-next
>> > >
>> > > in testcase: boot
>> > >
>> > > on test machine: qemu-system-x86_64 -enable-kvm -cpu host -smp 2 -m 2G
>> > >
>> > > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>> > >
>> > >
>> > > +------------------------------------------+------------+------------+
>> > > > | a4399c3b7b | dee160df82 |
>> > >
>> > > +------------------------------------------+------------+------------+
>> > > > boot_successes | 6 | 2 |
>> > > > boot_failures | 0 | 8 |
>> > > > BUG:KASAN:null-ptr-deref_in_l | 0 | 8 |
>> > > > BUG:unable_to_handle_kernel | 0 | 8 |
>> > > > Oops:#[##] | 0 | 8 |
>> > > > RIP:locks_remove_flock | 0 | 8 |
>> > > > Kernel_panic-not_syncing:Fatal_exception | 0 | 8 |
>> > >
>> > > +------------------------------------------+------------+------------+
>> > >
>> > >
>> > >
>> > > [ 41.286774] BUG: KASAN: null-ptr-deref in locks_remove_flock+0x147/0x180
>> > > [ 41.288812] Read of size 8 at addr 000000000000004e by task systemd-udevd/348
>> > > [ 41.290790]
>> > > [ 41.291485] CPU: 0 PID: 348 Comm: systemd-udevd Not tainted 4.20.0-rc1-00006-gdee160d #154
>> > > [ 41.293876] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>> > > [ 41.296488] Call Trace:
>> > > [ 41.297339] kasan_report+0x224/0x254
>> > > [ 41.298538] locks_remove_flock+0x147/0x180
>> > > [ 41.299936] ? flock_lock_inode+0x4b7/0x4b7
>> > > [ 41.301333] ? hlock_class+0x6f/0x8d
>> > > [ 41.302572] ? check_chain_key+0x102/0x15c
>> > > [ 41.303936] ? __lock_acquire+0x15ee/0x16bd
>> > > [ 41.305240] ? debug_show_all_locks+0x2bd/0x2bd
>> > > [ 41.306735] ? lookup_chain_cache+0xc9/0x14a
>> > > [ 41.308147] ? fsnotify+0x1c4/0x7ab
>> > > [ 41.309366] ? lock_downgrade+0x30a/0x30a
>> > > [ 41.310712] locks_remove_file+0xda/0x280
>> > > [ 41.312052] ? locks_remove_posix+0x3ba/0x3ba
>> > > [ 41.313397] ? __fsnotify_parent+0x82/0x1aa
>> > > [ 41.314571] ? fsnotify_sb_delete+0x373/0x373
>> > > [ 41.315967] ? ___might_sleep+0x12b/0x290
>> > > [ 41.317315] ? in_sched_functions+0x30/0x30
>> > > [ 41.318701] ? __might_sleep+0x2f/0xbf
>> > > [ 41.319976] __fput+0x1a1/0x2fc
>> > > [ 41.321062] ? file_free_rcu+0x62/0x62
>> > > [ 41.322132] ? in_sched_functions+0x30/0x30
>> > > [ 41.323451] ? mark_held_locks+0x67/0x81
>> > > [ 41.324770] ? _raw_spin_unlock_irq+0x24/0x2d
>> > > [ 41.326202] task_work_run+0x122/0x16c
>> > > [ 41.327485] ? task_work_cancel+0x13d/0x13d
>> > > [ 41.328869] ? task_work_add+0xc7/0x116
>> > > [ 41.330043] ? mark_held_locks+0x67/0x81
>> > > [ 41.331368] ? prepare_exit_to_usermode+0x18a/0x296
>> > > [ 41.332950] prepare_exit_to_usermode+0x1d4/0x296
>> > > [ 41.334476] ? enter_from_user_mode+0x2e/0x2e
>> > > [ 41.335893] ? fput+0x7a/0xae
>> > > [ 41.336961] ? filp_close+0xf7/0x122
>> > > [ 41.338196] ? __ia32_sys_creat+0x31/0x31
>> > > [ 41.339543] syscall_return_slowpath+0x23d/0x268
>> > > [ 41.341049] ? prepare_exit_to_usermode+0x296/0x296
>> > > [ 41.342625] ? fd_install+0x32/0x32
>> > > [ 41.343832] ? ksys_write+0xf1/0x124
>> > > [ 41.345028] ? mark_held_locks+0x67/0x81
>> > > [ 41.346310] do_syscall_64+0xf3/0x119
>> > > [ 41.347573] ? syscall_return_slowpath+0x268/0x268
>> > > [ 41.349075] ? lockdep_hardirqs_off+0x103/0x129
>> > > [ 41.350458] ? trace_hardirqs_off_thunk+0x1a/0x1c
>> > > [ 41.351971] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> > > [ 41.353604] RIP: 0033:0x7f31c39fe250
>> > > [ 41.354838] Code: 73 01 c3 48 8b 0d 58 7d 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 79 c1 20 00 00 75 10 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ee fb ff ff 48 89 04 24
>> > > [ 41.360261] RSP: 002b:00007fffc28371d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
>> > > [ 41.362406] RAX: 0000000000000000 RBX: 0000000000000007 RCX: 00007f31c39fe250
>> > > [ 41.364543] RDX: 000000000aba9500 RSI: 0000000000000000 RDI: 0000000000000007
>> > > [ 41.366593] RBP: 00007f31c48b6708 R08: 0000000000000045 R09: 0000000000000018
>> > > [ 41.368739] R10: 00005569133cb718 R11: 0000000000000246 R12: 0000000000000000
>> > > [ 41.370901] R13: 00005569133c26c0 R14: 0000000000000003 R15: 000000000000000e
>> > > [ 41.373009] ==================================================================
>> > > [ 41.375220] Disabling lock debugging due to kernel taint
>> > > [ 41.973175] BUG: unable to handle kernel NULL pointer dereference at 000000000000024e
>> > > [ 41.975580] PGD 0 P4D 0
>> > > [ 41.976496] Oops: 0000 [#1] KASAN PTI
>> > > [ 41.977678] CPU: 0 PID: 386 Comm: systemd-udevd Tainted: G B 4.20.0-rc1-00006-gdee160d #154
>> > > [ 41.980388] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>> > > [ 41.982865] RIP: 0010:locks_remove_flock+0x147/0x180
>> > > [ 41.984361] Code: ff ff 4c 8d 64 24 68 49 8d bc 24 d8 00 00 00 e8 7c d2 f3 ff 48 8b ac 24 40 01 00 00 48 85 ed 74 17 48 8d 7d 08 e8 66 d2 f3 ff <48> 8b 45 08 48 85 c0 74 05 4c 89 e7 ff d0 48 b8 00 00 00 00 00 fc
>> > > [ 41.989211] RSP: 0018:ffff880050ae7858 EFLAGS: 00010247
>> > > [ 41.990806] RAX: 0000000000000007 RBX: 1ffff1000a15cf0c RCX: ffffffff8136ab82
>> > > [ 41.992826] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 000000000000024e
>> > > [ 41.994856] RBP: 0000000000000246 R08: 0000000000000007 R09: 0000000000000000
>> > > [ 41.996872] R10: ffff880050ae75d8 R11: ffff880050ae7b0f R12: ffff880050ae78c0
>> > > [ 41.998897] R13: dffffc0000000000 R14: ffff88004f658150 R15: ffff880057578d58
>> > > [ 42.000912] FS: 00007f31c48b68c0(0000) GS:ffffffff83ac6000(0000) knlGS:0000000000000000
>> > > [ 42.003090] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> > > [ 42.004780] CR2: 000000000000024e CR3: 0000000051e30004 CR4: 00000000000606b0
>> > > [ 42.006814] Call Trace:
>> > > [ 42.007697] ? flock_lock_inode+0x4b7/0x4b7
>> > > [ 42.008999] ? debug_lockdep_rcu_enabled+0x26/0x51
>> > > [ 42.010343] ? debug_lockdep_rcu_enabled+0x26/0x51
>> > > [ 42.011765] ? __lock_acquire+0xf7/0x16bd
>> > > [ 42.013024] ? debug_lockdep_rcu_enabled+0x26/0x51
>> > > [ 42.014492] ? lockdep_rcu_suspicious+0xc5/0xc5
>> > > [ 42.015880] ? lock_downgrade+0x30a/0x30a
>> > > [ 42.017143] ? debug_show_all_locks+0x2bd/0x2bd
>> > > [ 42.018424] ? debug_lockdep_rcu_enabled+0x26/0x51
>> > > [ 42.019701] ? fsnotify+0x1c4/0x7ab
>> > > [ 42.020841] locks_remove_file+0xda/0x280
>> > > [ 42.022120] ? locks_remove_posix+0x3ba/0x3ba
>> > > [ 42.023477] ? locks_remove_posix+0x11c/0x3ba
>> > > [ 42.024815] ? __fsnotify_parent+0x82/0x1aa
>> > > [ 42.026137] ? fsnotify_sb_delete+0x373/0x373
>> > > [ 42.027495] ? ___might_sleep+0x12b/0x290
>> > > [ 42.028760] ? in_sched_functions+0x30/0x30
>> > > [ 42.030014] ? __might_sleep+0x2f/0xbf
>> > > [ 42.031098] __fput+0x1a1/0x2fc
>> > > [ 42.032150] ? file_free_rcu+0x62/0x62
>> > > [ 42.033344] ? in_sched_functions+0x30/0x30
>> > > [ 42.034673] ? trace_irq_disable_rcuidle+0x1f4/0x1f4
>> > > [ 42.036165] ? preempt_schedule_common+0x35/0x35
>> > > [ 42.037572] ? __kasan_slab_free+0xd9/0xfa
>> > > [ 42.038865] task_work_run+0x122/0x16c
>> > > [ 42.040067] ? task_work_cancel+0x13d/0x13d
>> > > [ 42.041373] ? task_work_add+0xc7/0x116
>> > > [ 42.042610] prepare_exit_to_usermode+0x1d4/0x296
>> > > [ 42.044044] ? enter_from_user_mode+0x2e/0x2e
>> > > [ 42.045402] ? fput+0x7a/0xae
>> > > [ 42.046422] ? filp_close+0xf7/0x122
>> > > [ 42.047571] ? __ia32_sys_creat+0x31/0x31
>> > > [ 42.048831] ? ptrace_report_syscall+0xad/0xad
>> > > [ 42.050382] syscall_return_slowpath+0x23d/0x268
>> > > [ 42.051784] ? prepare_exit_to_usermode+0x296/0x296
>> > > [ 42.053250] ? fd_install+0x32/0x32
>> > > [ 42.054341] ? kmem_cache_free+0xbf/0x101
>> > > [ 42.055620] ? do_sys_open+0x13d/0x168
>> > > [ 42.056812] do_syscall_64+0xf3/0x119
>> > > [ 42.057995] ? syscall_return_slowpath+0x268/0x268
>> > > [ 42.059460] ? lockdep_hardirqs_off+0x19/0x129
>> > > [ 42.060820] ? trace_hardirqs_off_thunk+0x1a/0x1c
>> > > [ 42.062196] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> > > [ 42.063639] RIP: 0033:0x7f31c39fe250
>> > > [ 42.064798] Code: 73 01 c3 48 8b 0d 58 7d 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 79 c1 20 00 00 75 10 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ee fb ff ff 48 89 04 24
>> > > [ 42.069903] RSP: 002b:00007fffc28323a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
>> > > [ 42.072126] RAX: 0000000000000000 RBX: 000000000000000f RCX: 00007f31c39fe250
>> > > [ 42.074153] RDX: 00007f31c39e8b58 RSI: 0000000000000000 RDI: 000000000000000f
>> > > [ 42.076185] RBP: 00007f31c48b6708 R08: 36b3f544af500741 R09: 0000000000000001
>> > > [ 42.078211] R10: 0000000000000116 R11: 0000000000000246 R12: 0000000000000002
>> > > [ 42.080237] R13: 0000000000000000 R14: 00005569133c1b50 R15: 000000000000000f
>> > > [ 42.082273] CR2: 000000000000024e
>> > > [ 42.083438] ---[ end trace b25bd2587e58b9b9 ]---
>> > >
>> > >
>> > > To reproduce:
>> > >
>> > > git clone https://github.com/intel/lkp-tests.git
>> > > cd lkp-tests
>> > > bin/lkp qemu -k <bzImage> job-script # job-script is attached in this email
>> > >
>> > >
>> > >
>> > > Thanks,
>> > > lkp
>> >
>> > Thanks LKP,
>> >
>> > I think I see the problem. locks_remove_flock calls flock_make_lock and
>> > passes it a pointer to a file_lock that lives on the stack. That
>> > file_lock is not zeroed out beforehand, and fl_ops is not overwritten
>> > during the initialization in flock_make_lock.
>> >
>> > I went ahead and updated this patch to zero out the file_lock structure
>> > in locks_remove_flock.
>>
>> Should the zeroing out part perhaps be part of flock_make_lock()? That
>> way we can either pass in fl == NULL and get the lock automatically
>> allocated, or if we pass in fl != NULL and then get it zeroed out by
>> flock_make_lock(), so callers don't have to bother with it.
>>
>> That said, the API is not public and there's only one user, so this is
>> somewhat moot.
>>
>
> Yeah, I'm inclined to just do the minimum to fix this one up. We can
> revisit it later with a cleanup patch though if we feel the need.

Thanks for fixing this up Jeff, though I think we really need
to call locks_init_lock() on the fl, either in flock_make_lock() or
locks_remove_lock().

Thanks,
NeilBrown

>
>> In either case, I can confirm that the new version with zeroed out
>> file_lock structure removes this issue that I was seeing on various
>> Tegra boards, so:
>>
>> Tested-by: Thierry Reding <treding@xxxxxxxxxx>
>
> Thanks for testing it! The fix should be in the next linux-next.
> --
> Jeff Layton <jlayton@xxxxxxxxxx>

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