netdev - Re: KASAN: use-after-free Read in vgem_gem_dumb

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Date:   Mon, 3 Feb 2020 12:06:19 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     syzbot <syzbot+0dc4444774d419e916c8@...kaller.appspotmail.com>,
        Dave Airlie <airlied@...ux.ie>,
        Alex Deucher <alexander.deucher@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        "Wilson, Chris" <chris@...is-wilson.co.uk>,
        Christian König <christian.koenig@....com>,
        David Miller <davem@...emloft.net>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Emil Velikov <emil.velikov@...labora.com>,
        "Anholt, Eric" <eric@...olt.net>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <seanpaul@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in vgem_gem_dumb_create

On Sun, Feb 02, 2020 at 02:19:18PM +0100, Daniel Vetter wrote:
> On Fri, Jan 31, 2020 at 11:28 PM syzbot
> <syzbot+0dc4444774d419e916c8@...kaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    39bed42d Merge tag 'for-linus-hmm' of git://git.kernel.org..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=179465bee00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2646535f8818ae25
> > dashboard link: https://syzkaller.appspot.com/bug?extid=0dc4444774d419e916c8
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16251279e00000
> >
> > The bug was bisected to:
> >
> > commit 7611750784664db46d0db95631e322aeb263dde7
> > Author: Alex Deucher <alexander.deucher@....com>
> > Date:   Wed Jun 21 16:31:41 2017 +0000
> >
> >     drm/amdgpu: use kernel is_power_of_2 rather than local version
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11628df1e00000
> > final crash:    https://syzkaller.appspot.com/x/report.txt?x=13628df1e00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15628df1e00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+0dc4444774d419e916c8@...kaller.appspotmail.com
> > Fixes: 761175078466 ("drm/amdgpu: use kernel is_power_of_2 rather than local version")
> 
> Aside: This bisect line is complete nonsense ... I'm kinda at the
> point where I'm assuming that syzbot bisect results are garbage, which
> is maybe not what we want. I guess much stricter filtering for noise
> is needed, dunno.
> -Danile

With race conditions the git bisect is often nonsense.

regards,
dan carpenter