On Fri, Jun 8, 2018 at 4:31 AM, Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > Dmitry Vyukov wrote: >> On Tue, Jun 5, 2018 at 3:45 PM, Tetsuo Handa >> <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: >> > Dmitry, can you assign VM resources for a git tree for this bug? This bug wants to fight >> > against https://github.com/google/syzkaller/blob/master/docs/syzbot.md#no-custom-patches ... >> >> Hi Tetsuo, >> >> Most of the reasons for not doing it still stand. A syzkaller instance >> will produce not just this bug, it will produce hundreds of different >> bugs. Then the question is: what to do with these bugs? Report all to >> mailing lists? > > Is it possible to add linux-next.git tree as a target for fuzzing? If yes, > we can try debug patches easily, in addition to find bugs earlier than now. syzbot tested linux-next and mmotm initially, but they were removed at the request of kernel developers. See: https://groups.google.com/d/msg/syzkaller/0H0LHW_ayR8/dsK5qGB_AQAJ and: https://groups.google.com/d/msg/syzkaller-bugs/FeAgni6Atlk/U0JGoR0AAwAJ Indeed, linux-next produces around 50 assorted one-off unexplainable bug reports. >> I think the solution here is just to run syzkaller instance locally. >> It's just a program anybody can run it on any kernel with any custom >> patches. Moreover for local instance it's also possible to limit set >> of tested syscalls to increase probability of hitting this bug and at >> the same time filter out most of other bugs. > > If this bug is reproducible with VM resources individual developer can afford... > > Since my Linux development environment is VMware guests on a Windows PC, I can't > run VM instance which needs KVM acceleration. Also, due to security policy, I can't > utilize external VM resources available on the Internet, as well as I can't use ssh > and git protocols. Speak of this bug, even with a lot of VM instances, syzbot can > reproduce this bug only once or twice per a day. Thus, the question for me boils > down to, whether I can reproduce this bug using one VMware guest instance with 4GB > of memory. Effectively, I don't have access to environments for running syzkaller > instance... Well, I don't know what to say, it does require some resources. >> Do we have any idea about the guilty subsystem? You mentioned >> bdi_unregister, why? What would be the set of syscalls to concentrate >> on? >> I will do a custom run when I get around to it, if nobody else beats me to it. > > Because bdi_unregister() does "bdi->dev = NULL;" which wb_workfn() is hitting > NULL pointer dereference. Right, wb_workfn is not a generic function, it's fs-specific function. Trying to reproduce this locally now.
