linux-kernel - Re: KASAN: slab-out-of-bounds Read in fbcon_get

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Date:   Thu, 5 Dec 2019 12:36:56 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        syzbot <syzbot+4455ca3b3291de891abc@...kaller.appspotmail.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI <dri-devel@...ts.freedesktop.org>, ghalat@...hat.com,
        Gleb Natapov <gleb@...nel.org>, gwshan@...ux.vnet.ibm.com,
        "H. Peter Anvin" <hpa@...or.com>, James Morris <jmorris@...ei.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        KVM list <kvm@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Russell Currey <ruscur@...sell.cc>,
        Sam Ravnborg <sam@...nborg.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, stewart@...ux.vnet.ibm.com,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Kentaro Takeda <takedakn@...data.co.jp>,
        Thomas Gleixner <tglx@...utronix.de>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: KASAN: slab-out-of-bounds Read in fbcon_get_font

On Thu, Dec 5, 2019 at 11:41 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2019/12/05 19:22, Paolo Bonzini wrote:
> > Ah, and because the machine is a KVM guest, kvm_wait appears in a lot of
> > backtrace and I get to share syzkaller's joy every time. :)
> >
> > This bisect result is bogus, though Tetsuo found the bug anyway.
> > Perhaps you can exclude commits that only touch architectures other than
> > x86?
> >
>
> It would be nice if coverage functionality can extract filenames in the source
> code and supply the list of filenames as arguments for bisect operation.
>
> Also, (unrelated but) it would be nice if we can have "make yes2modconfig"
> target which converts CONFIG_FOO=y to CONFIG_FOO=m if FOO is tristate.
> syzbot is testing kernel configs close to "make allyesconfig" but I want to
> save kernel rebuild time by disabling unrelated functionality when manually
> "debug printk()ing" kernels.

I thought that maybe sed "s#=y#=m#g" && make olddefconfig will do, but
unfortunately, it turns off non-tristate configs...

$ egrep "CONFIG_MEMORY_HOTPLUG|CONFIG_TCP_CONG_DCTCP" .config
CONFIG_MEMORY_HOTPLUG=y
CONFIG_TCP_CONG_DCTCP=y
# sed -i "s/CONFIG_MEMORY_HOTPLUG=y/CONFIG_MEMORY_HOTPLUG=m/g" .config
# sed -i "s/CONFIG_TCP_CONG_DCTCP=y/CONFIG_TCP_CONG_DCTCP=m/g" .config
# egrep "CONFIG_MEMORY_HOTPLUG|CONFIG_TCP_CONG_DCTCP" .config
CONFIG_MEMORY_HOTPLUG=m
CONFIG_TCP_CONG_DCTCP=m
# make olddefconfig
# egrep "CONFIG_MEMORY_HOTPLUG|CONFIG_TCP_CONG_DCTCP" .config
# CONFIG_MEMORY_HOTPLUG is not set
CONFIG_TCP_CONG_DCTCP=m