Re: linux 5.14.3: free_user_ns causes NULL pointer dereference

Yu Zhao
2021-10-06T06:22:54Z

On Tue, Oct 5, 2021 at 8:12 PM Hillf Danton <hdanton@sina.com> wrote:
>
> On Thu, 30 Sep 2021 16:27:34 -0600 Yu Zhao wrote:
> >On Thu, Sep 30, 2021 at 7:06 AM Alexey Gladkov <legion@kernel.org> wrote:
> >>
> >> On Wed, Sep 29, 2021 at 09:39:06PM +0000, Jordan Glover wrote:
> >> > > I'm still investigating, but I would like to rule out one option.
> >> > >
> >> > > Could you check out the patch?
> >> >
> >> >
> >> > Thx, I added it to my kernel and will report in few days.
> >> > Does this patch try to fix the issue or make it easier to track?
> >>
> >> I suspect the error is caused by a race between allow_ucounts() and
> >> put_ucounts(). I think this patch could solve the problem.
> >
> >Thanks for your help. Still can reproduce the problem with the change suggested.
> >
> >[ 7761.885966] ==================================================================
> >[ 7761.893462] BUG: KASAN: use-after-free in dec_ucount+0x50/0xd8
> >[ 7761.899491] Write of size 8 at addr ffffff80c537b140 by task
> >kworker/u16:3/10303
> >[ 7761.907110]
> >[ 7761.908668] CPU: 0 PID: 10303 Comm: kworker/u16:3 Not tainted
> >5.14.0-lockdep+ #1
> >[ 7761.916289] Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
> >[ 7761.923021] Workqueue: netns cleanup_net
> >[ 7761.927106] Call trace:
> >[ 7761.929648] dump_backtrace+0x0/0x42c
> >[ 7761.933442] show_stack+0x24/0x30
> >[ 7761.936878] dump_stack_lvl+0xd0/0x100
> >[ 7761.940763] print_address_description+0x30/0x304
> >[ 7761.945628] kasan_report+0x190/0x1d8
> >[ 7761.949418] kasan_check_range+0x1ac/0x1bc
> >[ 7761.953655] __kasan_check_write+0x44/0x54
> >[ 7761.957891] dec_ucount+0x50/0xd8
> >[ 7761.961334] cleanup_net+0x630/0x718
> >[ 7761.965036] process_one_work+0x7b4/0x10ec
> >[ 7761.969274] worker_thread+0x800/0xcf4
> >[ 7761.973152] kthread+0x2a8/0x358
> >[ 7761.976496] ret_from_fork+0x10/0x18
> >[ 7761.980201]
> >[ 7761.981761] Allocated by task 4840:
> >[ 7761.985366] kasan_save_stack+0x38/0x68
> >[ 7761.989342] __kasan_kmalloc+0x9c/0xb8
> >[ 7761.993222] kmem_cache_alloc_trace+0x2a4/0x370
> >[ 7761.997905] alloc_ucounts+0x150/0x374
> >[ 7762.001787] set_cred_ucounts+0x198/0x248
> >[ 7762.005935] __sys_setresuid+0x31c/0x4f8
> >[ 7762.009993] __arm64_sys_setresuid+0x84/0x98
> >[ 7762.014410] invoke_syscall+0xd4/0x2c8
> >[ 7762.018292] el0_svc_common+0x124/0x200
> >[ 7762.022265] do_el0_svc_compat+0x54/0x64
> >[ 7762.026325] el0_svc_compat+0x24/0x34
> >[ 7762.030124] el0t_32_sync_handler+0xc0/0xf0
> >[ 7762.034451] el0t_32_sync+0x19c/0x1a0
> >[ 7762.038241]
> >[ 7762.039799] Freed by task 0:
> >[ 7762.042778] kasan_save_stack+0x38/0x68
> >[ 7762.046747] kasan_set_track+0x28/0x3c
> >[ 7762.050625] kasan_set_free_info+0x28/0x4c
> >[ 7762.054857] ____kasan_slab_free+0x118/0x164
> >[ 7762.059277] __kasan_slab_free+0x18/0x28
> >[ 7762.063339] kfree+0x2f8/0x500
> >[ 7762.066505] put_ucounts+0x11c/0x134
> >[ 7762.070209] put_cred_rcu+0x1bc/0x35c
> >[ 7762.074006] rcu_core+0xa68/0x1b20
> >[ 7762.077538] rcu_core_si+0x1c/0x28
> >[ 7762.081061] __do_softirq+0x4bc/0xedc
> >[ 7762.084851]
> >[ 7762.086401] The buggy address belongs to the object at ffffff80c537b100
> >[ 7762.086401] which belongs to the cache kmalloc-256 of size 256
> >[ 7762.099267] The buggy address is located 64 bytes inside of
> >[ 7762.099267] 256-byte region [ffffff80c537b100, ffffff80c537b200)
> >[ 7762.111248] The buggy address belongs to the page:
> >[ 7762.116185] page:fffffffe0314de00 refcount:1 mapcount:0
> >mapping:0000000000000000 index:0xffffff80c537ad00 pfn:0x145378
> >[ 7762.127180] head:fffffffe0314de00 order:3 compound_mapcount:0
> >compound_pincount:0
> >[ 7762.134881] flags: 0x8000000000010200(slab|head|zone=2)
> >[ 7762.140286] raw: 8000000000010200 fffffffe02799408 fffffffe02020808
> >ffffff808000c980
> >[ 7762.148263] raw: ffffff80c537ad00 0000000000200004 00000001ffffffff
> >0000000000000000
> >[ 7762.156228] page dumped because: kasan: bad access detected
> >[ 7762.161974]
> >[ 7762.163532] Memory state around the buggy address:
> >[ 7762.168475] ffffff80c537b000: fc fc fc fc fc fc fc fc fc fc fc fc
> >fc fc fc fc
> >[ 7762.175915] ffffff80c537b080: fc fc fc fc fc fc fc fc fc fc fc fc
> >fc fc fc fc
> >[ 7762.183346] >ffffff80c537b100: fa fb fb fb fb fb fb fb fb fb fb fb
> >fb fb fb fb
> >[ 7762.190774] ^
> >[ 7762.196258] ffffff80c537b180: fb fb fb fb fb fb fb fb fb fb fb fb
> >fb fb fb fb
> >[ 7762.203689] ffffff80c537b200: fc fc fc fc fc fc fc fc fc fc fc fc
> >fc fc fc fc
> >[ 7762.211125] ==================================================================
>
> Could you please check if it is due to count underflow? Given nothing wrong
> on the other side based on the efforts
> "We looked through the users of put_ucounts and we don't see any obvious buggy
> users that would be freeing the data structure early."

Thanks, Hillf.

Still can reproduce the problem without triggering the warning.

[ 7965.795189] ==================================================================
[ 7965.802642] BUG: KASAN: use-after-free in dec_ucount+0x50/0xd8
[ 7965.808653] Write of size 8 at addr ffffff8090294920 by task kworker/7:0/7002
[ 7965.815990]
[ 7965.817536] CPU: 7 PID: 7002 Comm: kworker/7:0 Not tainted 5.14.0-lockdep+ #2
[ 7965.824870] Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
[ 7965.831576] Workqueue: events free_user_ns
[ 7965.835810] Call trace:
[ 7965.838338] dump_backtrace+0x0/0x42c
[ 7965.842119] show_stack+0x24/0x30
[ 7965.845540] dump_stack_lvl+0xd0/0x100
[ 7965.849401] print_address_description+0x30/0x304
[ 7965.854248] kasan_report+0x190/0x1d8
[ 7965.858016] kasan_check_range+0x1ac/0x1bc
[ 7965.862236] __kasan_check_write+0x44/0x54
[ 7965.866463] dec_ucount+0x50/0xd8
[ 7965.869876] free_user_ns+0x1b0/0x288
[ 7965.873645] process_one_work+0x7b4/0x10ec
[ 7965.877871] worker_thread+0x800/0xcf4
[ 7965.881729] kthread+0x2a8/0x358
[ 7965.885057] ret_from_fork+0x10/0x18
[ 7965.888746]
[ 7965.890288] Allocated by task 19167:
[ 7965.893976] kasan_save_stack+0x38/0x68
[ 7965.897923] __kasan_kmalloc+0x9c/0xb8
[ 7965.901782] __kmalloc+0x2c8/0x3c0
[ 7965.905287] kvmalloc_node+0x64/0x104
[ 7965.909065] v4l2_ctrl_new+0x478/0xc6c
[ 7965.912923] v4l2_ctrl_new_std+0x280/0x374
[ 7965.917136] venc_ctrl_init+0x4c4/0x7c8 [venus_enc]
[ 7965.922170] venc_open+0x218/0x668 [venus_enc]
[ 7965.926748] v4l2_open+0x158/0x234
[ 7965.930255] chrdev_open+0x17c/0x37c
[ 7965.933942] do_dentry_open+0x504/0xa44
[ 7965.937889] vfs_open+0x84/0x98
[ 7965.941124] path_openat+0x1980/0x1fac
[ 7965.944991] do_filp_open+0x19c/0x2c0
[ 7965.948767] do_sys_openat2+0xb8/0x298
[ 7965.952628] do_sys_open+0x124/0x15c
[ 7965.956309] __arm64_compat_sys_openat+0xa4/0xbc
[ 7965.961060] invoke_syscall+0xd4/0x2c8
[ 7965.964920] el0_svc_common+0x124/0x200
[ 7965.968873] do_el0_svc_compat+0x54/0x64
[ 7965.972915] el0_svc_compat+0x24/0x34
[ 7965.976688] el0t_32_sync_handler+0xc0/0xf0
[ 7965.980999] el0t_32_sync+0x19c/0x1a0
[ 7965.984781]
[ 7965.986330] Last potentially related work creation:
[ 7965.991342] kasan_save_stack+0x38/0x68
[ 7965.995294] kasan_record_aux_stack+0xdc/0x108
[ 7965.999866] insert_work+0x60/0x22c
[ 7966.003458] __queue_work+0xae8/0xe74
[ 7966.007223] queue_work_on+0x100/0x148
[ 7966.011076] drm_atomic_helper_commit+0x18c/0x1f4
[ 7966.015917] drm_atomic_nonblocking_commit+0xc4/0xdc
[ 7966.021018] drm_mode_atomic_ioctl+0x89c/0xaa0
[ 7966.025590] drm_ioctl_kernel+0x15c/0x260
[ 7966.029720] drm_ioctl+0x460/0x828
[ 7966.033229] drm_compat_ioctl+0x1bc/0x230
[ 7966.037370] __arm64_compat_sys_ioctl+0x1b0/0x1c4
[ 7966.042216] invoke_syscall+0xd4/0x2c8
[ 7966.046071] el0_svc_common+0x124/0x200
[ 7966.050015] do_el0_svc_compat+0x54/0x64
[ 7966.054053] el0_svc_compat+0x24/0x34
[ 7966.057819] el0t_32_sync_handler+0xc0/0xf0
[ 7966.062119] el0t_32_sync+0x19c/0x1a0
[ 7966.065884]
[ 7966.067424] Second to last potentially related work creation:
[ 7966.073329] kasan_save_stack+0x38/0x68
[ 7966.077271] kasan_record_aux_stack+0xdc/0x108
[ 7966.081837] insert_work+0x60/0x22c
[ 7966.085434] __queue_work+0xae8/0xe74
[ 7966.089202] queue_work_on+0x100/0x148
[ 7966.093060] drm_atomic_helper_commit+0x18c/0x1f4
[ 7966.097900] drm_atomic_nonblocking_commit+0xc4/0xdc
[ 7966.103000] drm_mode_atomic_ioctl+0x89c/0xaa0
[ 7966.107572] drm_ioctl_kernel+0x15c/0x260
[ 7966.111697] drm_ioctl+0x460/0x828
[ 7966.115200] drm_compat_ioctl+0x1bc/0x230
[ 7966.119323] __arm64_compat_sys_ioctl+0x1b0/0x1c4
[ 7966.124161] invoke_syscall+0xd4/0x2c8
[ 7966.128016] el0_svc_common+0x124/0x200
[ 7966.131962] do_el0_svc_compat+0x54/0x64
[ 7966.135993] el0_svc_compat+0x24/0x34
[ 7966.139762] el0t_32_sync_handler+0xc0/0xf0
[ 7966.144067] el0t_32_sync+0x19c/0x1a0
[ 7966.147837]
[ 7966.149374] The buggy address belongs to the object at ffffff8090294900
[ 7966.149374] which belongs to the cache kmalloc-256 of size 256
[ 7966.162218] The buggy address is located 32 bytes inside of
[ 7966.162218] 256-byte region [ffffff8090294900, ffffff8090294a00)
[ 7966.174174] The buggy address belongs to the page:
[ 7966.179101] page:fffffffe0240a400 refcount:1 mapcount:0
mapping:0000000000000000 index:0xffffff8090294900 pfn:0x110290
[ 7966.190079] head:fffffffe0240a400 order:3 compound_mapcount:0
compound_pincount:0
[ 7966.197760] flags: 0x8000000000010200(slab|head|zone=2)
[ 7966.203137] raw: 8000000000010200 fffffffe002f3c08 fffffffe023f9008
ffffff808000c980
[ 7966.211086] raw: ffffff8090294900 0000000000200005 00000001ffffffff
0000000000000000
[ 7966.219034] page dumped because: kasan: bad access detected
[ 7966.224763]
[ 7966.226300] Memory state around the buggy address:
[ 7966.231228] ffffff8090294800: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 7966.238641] ffffff8090294880: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 7966.246055] >ffffff8090294900: fb fb fb fb fb fb fb fb fb fb fb fb
fb fb fb fb
[ 7966.253466] ^
[ 7966.257849] ffffff8090294980: fb fb fb fb fb fb fb fb fb fb fb fb
fb fb fb fb
[ 7966.265267] ffffff8090294a00: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 7966.272678] ==================================================================