Hi Dmitry, On 10/31/18 9:49 AM, Helen Koike wrote: > Hi Dmitry, > > On 10/31/18 7:46 AM, Hans Verkuil wrote: >> On 10/30/2018 03:02 PM, Dmitry Vyukov wrote: >>> Hello Helen and linux-media, >>> >>> I've attended your talk "Shifting Media App Development into High >>> Gear" on OSS Summit last week and approached you with some questions >>> if/how this can be used for kernel testing. Thanks, turn out to be a >>> very useful talk! > > Great, I am glad it was useful :) > >>> >>> I am working on syzkaller/syzbot, continuous kernel fuzzing system: >>> https://github.com/google/syzkaller >>> https://github.com/google/syzkaller/blob/master/docs/syzbot.md >>> https://syzkaller.appspot.com >>> >>> After simply enabling CONFIG_VIDEO_VIMC, CONFIG_VIDEO_VIM2M, >>> CONFIG_VIDEO_VIVID, CONFIG_VIDEO_VICODEC syzbot has found 8 bugs in >>> media subsystem in just 24 hours: >>> >>> KASAN: use-after-free Read in vb2_mmap >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/XGGH69jMWQ0/S8vfxgEmCgAJ >>> >>> KASAN: use-after-free Write in __vb2_cleanup_fileio >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/qKKhsZVPo3o/P6AB2of2CQAJ >>> >>> WARNING in __vb2_queue_cancel >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/S29GU_NtfPY/ZvAz8UDtCQAJ >>> >>> divide error in vivid_vid_cap_s_dv_timings >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/GwF5zGBCfyg/wnuWmW_sCQAJ >> >> Should be fixed by https://patchwork.linuxtv.org/patch/52641/ >> >>> >>> KASAN: use-after-free Read in wake_up_if_idle >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/aBWb_yV1kiI/sWQO63fkCQAJ >>> >>> KASAN: use-after-free Read in __vb2_perform_fileio >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/MdFCZHz0LUQ/qSK_bFbcCQAJ >>> >>> INFO: task hung in vivid_stop_generating_vid_cap >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/F_KFW6PVyTA/wTBeHLfTCQAJ >>> >>> KASAN: null-ptr-deref Write in kthread_stop >>> https://groups.google.com/forum/#!msg/syzkaller-bugs/u0AGnYvSlf4/fUiyfA_TCQAJ >> >> These last two should be fixed by https://patchwork.linuxtv.org/patch/52640/ >> >> Haven't figured out the others yet (hope to get back to that next week). >> >>> >>> Based on this I think if we put more effort into media fuzzing, it >>> will be able to find dozens more. >> >> Yeah, this is good stuff. Thank you for setting this up. > > Agreed, Dmitry thank you for doing this. > >> >>> >>> syzkaller needs descriptions of kernel interfaces to efficiently cover >>> a subsystem. For example, see: >>> https://github.com/google/syzkaller/blob/master/sys/linux/uinput.txt >>> Hopefully you can read it without much explanation, it basically >>> states that there is that node in /dev and here are ioctls and other >>> syscalls that are relevant for this device and here are types of >>> arguments and layout of involved data structures. >>> >>> Turned we actually have such descriptions for /dev/video* and /dev/v4l-subdev*: >>> https://github.com/google/syzkaller/blob/master/sys/linux/video4linux.txt >>> But we don't have anything for /dev/media*, fuzzer merely knows that >>> it can open the device: >>> https://github.com/google/syzkaller/blob/12b38f22c18c6109a5cc1c0238d015eef121b9b7/sys/linux/sys.txt#L479 >>> and then it will just blindly execute completely random workload on >>> it, e.g. most likely it won't be able to come up with a proper complex >>> structure layout for some ioctls. And I am actually not completely >>> sure about completeness and coverage of video4linux.txt descriptions >>> too as they were contributed by somebody interested in android >>> testing. >> >> A quick look suggests that it is based on the 4.9 videodev2.h, which ain't >> too bad. There are some differences between the 4.20 videodev2.h and the >> 4.9, but not too many. >> >>> >>> I wonder if somebody knowledgeable in /dev/media interface be willing >>> to contribute additional descriptions? >> >> We'll have to wait for 4.20-rc1 to be released since there are important >> additions to the media API. I can probably come up with something, I'm >> just not sure when I get around to it. Ping me in three weeks time if you >> haven't heard from me. >> >>> >>> We also have code coverage reports with the coverage fuzzer achieved >>> so far. Here in the Cover column: >>> https://syzkaller.appspot.com/#managers >>> e.g. this one (but note this is a ~80MB html file): >>> https://storage.googleapis.com/syzkaller/cover/ci-upstream-kasan-gce-root.html >>> This can be used to assess e.g. v4l coverage. But I don't know what's >>> coverable in general from syscalls and what's coverable via the stub >>> drivers in particular. So some expertise from media developers would >>> be helpful too. >> >> The four virtual drivers should give pretty decent coverage of the core >> code. Are you able to test with a 32-bit syzkaller application on a 64-bit >> kernel as well? That way the compat32 code is tested. >> >>> >>> Do I understand it correctly that when a process opens /dev/video* or >>> /dev/media* it gets a private instance of the device? In particular, >>> if several processes test this in parallel, will they collide? Or they >>> will stress separate objects? >> >> It actually depends on the driver. M2M devices will give you a private >> instance whenever you open it. Others do not, but you can call most ioctls >> in parallel. But after calling REQBUFS or CREATE_BUFS the filehandle that >> called those ioctls becomes owner of the device until the buffers are >> released. So other filehandles cannot do any streaming operations (EBUSY >> will be returned). >> >>> You also mentioned that one of the devices requires some complex setup >>> via configfs. Is this interface described somewhere? Do you think it's >>> more profitable to pre-setup some fixed configuration for each test >>> process? Or just give the setup interface to fuzzer and let it do >>> random setup? Or both? >> >> That's the vimc driver, but the configfs code isn't in yet. > > I'll try to submit it later this week (with documentation) :) I submitted the first version at: https://www.spinics.net/lists/linux-media/msg144244.html As soon as it is updated we can add it to fuzzer. I believe some pre-setup/fixed configuration would work. I don't know much about fuzzer's code, if you could give me some pointers I can help with that. Thanks Helen > >> >> Regards, >> >> Hans >> >>> >>> Thanks in advance >>> >> > > > Thanks > Helen >
