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[24.9.64.241]) by smtp.gmail.com with ESMTPSA id l23sm229649otk.79.2020.10.05.13.44.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 05 Oct 2020 13:44:21 -0700 (PDT) Subject: Re: KASAN: null-ptr-deref Write in event_handler To: Andrey Konovalov , Shuah Khan , Valentina Manea Cc: Greg Kroah-Hartman , LKML , USB list , syzkaller-bugs , syzbot , Nazime Hande Harputluoglu , Shuah Khan References: <000000000000810a4405b0ece316@google.com> From: Shuah Khan Message-ID: <2947473d-76cd-a663-049a-4d51a97e2a3e@linuxfoundation.org> Date: Mon, 5 Oct 2020 14:44:20 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/5/20 8:04 AM, Andrey Konovalov wrote: > On Mon, Oct 5, 2020 at 3:59 PM syzbot > wrote: >> >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: d3d45f82 Merge tag 'pinctrl-v5.9-2' of git://git.kernel.or.. >> git tree: upstream >> console output: https://syzkaller.appspot.com/x/log.txt?x=15781d8f900000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=89ab6a0c48f30b49 >> dashboard link: https://syzkaller.appspot.com/bug?extid=bf1a360e305ee719e364 >> compiler: gcc (GCC) 10.1.0-syz 20200507 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16cbaa7d900000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1364f367900000 >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+bf1a360e305ee719e364@syzkaller.appspotmail.com >> >> vhci_hcd: stop threads >> vhci_hcd: release socket >> vhci_hcd: disconnect device >> ================================================================== >> BUG: KASAN: null-ptr-deref in instrument_atomic_write include/linux/instrumented.h:71 [inline] >> BUG: KASAN: null-ptr-deref in atomic_fetch_add_relaxed include/asm-generic/atomic-instrumented.h:142 [inline] >> BUG: KASAN: null-ptr-deref in refcount_add include/linux/refcount.h:201 [inline] >> BUG: KASAN: null-ptr-deref in refcount_inc include/linux/refcount.h:241 [inline] >> BUG: KASAN: null-ptr-deref in get_task_struct include/linux/sched/task.h:104 [inline] >> BUG: KASAN: null-ptr-deref in kthread_stop+0x90/0x7e0 kernel/kthread.c:591 >> Write of size 4 at addr 000000000000001c by task kworker/u4:5/2519 >> >> CPU: 1 PID: 2519 Comm: kworker/u4:5 Not tainted 5.9.0-rc7-syzkaller #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >> Workqueue: usbip_event event_handler >> Call Trace: >> __dump_stack lib/dump_stack.c:77 [inline] >> dump_stack+0x198/0x1fd lib/dump_stack.c:118 >> __kasan_report mm/kasan/report.c:517 [inline] >> kasan_report.cold+0x5/0x37 mm/kasan/report.c:530 >> check_memory_region_inline mm/kasan/generic.c:186 [inline] >> check_memory_region+0x13d/0x180 mm/kasan/generic.c:192 >> instrument_atomic_write include/linux/instrumented.h:71 [inline] >> atomic_fetch_add_relaxed include/asm-generic/atomic-instrumented.h:142 [inline] >> refcount_add include/linux/refcount.h:201 [inline] >> refcount_inc include/linux/refcount.h:241 [inline] >> get_task_struct include/linux/sched/task.h:104 [inline] >> kthread_stop+0x90/0x7e0 kernel/kthread.c:591 >> vhci_shutdown_connection+0x170/0x2a0 drivers/usb/usbip/vhci_hcd.c:1015 >> event_handler+0x1a5/0x450 drivers/usb/usbip/usbip_event.c:78 >> process_one_work+0x94c/0x1670 kernel/workqueue.c:2269 >> worker_thread+0x64c/0x1120 kernel/workqueue.c:2415 >> kthread+0x3b5/0x4a0 kernel/kthread.c:292 >> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 >> ================================================================== >> Kernel panic - not syncing: panic_on_warn set ... >> CPU: 1 PID: 2519 Comm: kworker/u4:5 Tainted: G B 5.9.0-rc7-syzkaller #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >> Workqueue: usbip_event event_handler >> Call Trace: >> __dump_stack lib/dump_stack.c:77 [inline] >> dump_stack+0x198/0x1fd lib/dump_stack.c:118 >> panic+0x382/0x7fb kernel/panic.c:231 >> end_report+0x4d/0x53 mm/kasan/report.c:104 >> __kasan_report mm/kasan/report.c:520 [inline] >> kasan_report.cold+0xd/0x37 mm/kasan/report.c:530 >> check_memory_region_inline mm/kasan/generic.c:186 [inline] >> check_memory_region+0x13d/0x180 mm/kasan/generic.c:192 >> instrument_atomic_write include/linux/instrumented.h:71 [inline] >> atomic_fetch_add_relaxed include/asm-generic/atomic-instrumented.h:142 [inline] >> refcount_add include/linux/refcount.h:201 [inline] >> refcount_inc include/linux/refcount.h:241 [inline] >> get_task_struct include/linux/sched/task.h:104 [inline] >> kthread_stop+0x90/0x7e0 kernel/kthread.c:591 >> vhci_shutdown_connection+0x170/0x2a0 drivers/usb/usbip/vhci_hcd.c:1015 >> event_handler+0x1a5/0x450 drivers/usb/usbip/usbip_event.c:78 >> process_one_work+0x94c/0x1670 kernel/workqueue.c:2269 >> worker_thread+0x64c/0x1120 kernel/workqueue.c:2415 >> kthread+0x3b5/0x4a0 kernel/kthread.c:292 >> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 >> Kernel Offset: disabled >> Rebooting in 86400 seconds.. > > Hi Valentina and Shuah, > > There appears to be a race condition in the USB/IP vhci_hcd shutdown > procedure. It happens quite often during fuzzing with syzkaller, and > prevents us from going deeper into the USB/IP code. > > Could you advise us what would be the best fix for this? > Hi Andrey, Reading the comments for this routine, looks like there is an assumption that context begins cleanup and race conditions aren't considered. The right fix is holding vhci->lock and vdev->priv_lock to protect critical sections in this routine. I will send a patch for this. thanks, -- Shuah