linux-kernel - Re: general protection fault in syscall_return

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Message-ID: <20200312133442.GH11561@kadam>
Date:   Thu, 12 Mar 2020 16:34:42 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     syzbot <syzbot+cd66e43794b178bb5cd6@...kaller.appspotmail.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        syzkaller-bugs@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>
Subject: Re: general protection fault in syscall_return_slowpath

On Sun, Mar 08, 2020 at 09:29:04AM -0700, Andy Lutomirski wrote:
> On Sat, Mar 7, 2020 at 11:45 PM syzbot
> <syzbot+cd66e43794b178bb5cd6@...kaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    63623fd4 Merge tag 'for-linus' of git://git.kernel.org/pub..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=16cfeac3e00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=5d2e033af114153f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=cd66e43794b178bb5cd6
> > compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12a42329e00000
> >
> 
> I bet this is due to entirely missing input validation in
> con_font_copy() and/or fbcon_copy_font().

The only thing we use in con_font_copy() is op->height and we clamp it
to 0-MAX_NR_CONSOLES (64).

regards,
dan carpenter