On Tue, Nov 13, 2018 at 9:37 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 12 Nov 2018, syzbot wrote: > >> syzbot has found a reproducer for the following crash on: >> >> HEAD commit: e12e00e388de Merge tag 'kbuild-fixes-v4.20' of git://git.k.. >> git tree: upstream >> console output: https://syzkaller.appspot.com/x/log.txt?x=100e4ef5400000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=8f215f21f041a0d7 >> dashboard link: https://syzkaller.appspot.com/bug?extid=7634edaea4d0b341c625 >> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11ce6fbd400000 >> >> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> Reported-by: syzbot+7634edaea4d0b341c625@xxxxxxxxxxxxxxxxxxxxxxxxx > > I tried reproducing this bug on my own system, following the > instructions at > > https://github.com/google/syzkaller/blob/master/docs/executing_syzkaller_programs.md > > The reproducer failed to run properly. It produced the following > output: > > > $ ./syz-execprog -cover=0 -threaded=1 -repeat=1 -procs=4 /tmp/repro.syz > 2018/11/13 15:29:32 parsed 1 programs > 2018/11/13 15:29:32 executed programs: 0 > 2018/11/13 15:29:32 result: failed=false hanged=false err=executor 3: failed: tun: ioctl(TUNSETIFF) failed (errno 1) > loop failed (errno 0) > > > tun: ioctl(TUNSETIFF) failed (errno 1) > loop failed (errno 0) > > > The system is Fedora 28 running the 4.18.16-200.fc28.x86_64 kernel. > What should I do to investigate further? Hi Alan, Looking at "errno 1", it seems that syz-execprog doesn't have enough privileges to execute this ioctl, so you might need to run it as root. However the absence of a C reproducer points to the fact that this is some kind of a race condition. Those are quite sensitive to timing, and any difference in the used setup might affect their reproducibility. I would recommend building the exact kernel revision with the provided config. For me it took around 3 minutes to syz-execprog before I saw the WARNING. Thanks!
