On Fri, Apr 19, 2019 at 11:21 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > On Tue, Mar 26, 2019 at 2:10 PM syzbot > <syzbot+9c69c282adc4edd2b540@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > syzbot has bisected this bug to: > > > > commit 01b39dcc95680b04c7af5de7f39f577e9c4865e3 > > Author: Amir Goldstein <amir73il@xxxxxxxxx> > > Date: Fri May 11 08:15:15 2018 +0000 > > > > ovl: use inode_insert5() to hash a newly created inode > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=176da0cd200000 > > start commit: de6629eb Merge tag 'pci-v5.0-fixes-1' of git://git.kernel... > > git tree: upstream > > final crash: https://syzkaller.appspot.com/x/report.txt?x=14eda0cd200000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=10eda0cd200000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=edf1c3031097c304 > > dashboard link: https://syzkaller.appspot.com/bug?extid=9c69c282adc4edd2b540 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12c7a94f400000 > > > > Reported-by: syzbot+9c69c282adc4edd2b540@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: 01b39dcc9568 ("ovl: use inode_insert5() to hash a newly created > > inode") > > > > Dmitry, > > The root cause of this bug is that repro is mounting overlapping overlay > layers (i.e. upperdir=./file0,lowerdir=.:file0). > Miklos claimed that the fix should be to fail such mounts. > Below is a patch to test: > > #syz test: https://github.com/amir73il/linux.git ovl-check-overlap > > However, I see that this specific overlapping layers mount has already > mutated to several other repros out there, like the ones in this bug: > > https://syzkaller.appspot.com/bug?extid=a55ccfc8a853d3cff213 > > I believe that disallowing overlapping layers will silence some > bugs, whose root cause may be different. > > Besides doing the overlapping layers mount, this repro family also > does extensive access to overlay underlying layers concurrently > with overlay access and *that* is the root cause for most of these > "possible deadlock" bugs (some false positives and some real). > > Assuming that ovl-check-overlap will get merged, you may need to > hint syzkaller that overlapping layers is no longer a valid input or > maybe it will figure it out on its own?... Hi Amir, It should figure it out on its own, it's coverage-guided fuzzer. And unlearning things is easier then learning them :) But thanks for thinking about this. But maybe there is something else important in overlayfs that's not covered. Here you can see the current coverage of overlayfs: https://storage.googleapis.com/syzkaller/cover/ci-upstream-linux-next-kasan-gce-root.html#e2f448f0ca2e4397fd609ff8c42d4cd118411148
