Re: WARNING in drm_mode_createblob_ioctl

[Dmitry Vyukov]

On Wed, Nov 6, 2019 at 4:28 PM Daniel Vetter <daniel@xxxxxxxx> wrote:
>
> On Wed, Nov 6, 2019 at 4:23 PM Daniel Vetter <daniel@xxxxxxxx> wrote:
> >
> > On Wed, Nov 6, 2019 at 4:20 PM syzbot
> > <syzbot+fb77e97ebf0612ee6914@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > syzbot has bisected this bug to:
> > >
> > > commit 9e5a64c71b2f70ba530f8156046dd7dfb8a7a0ba
> > > Author: Kees Cook <keescook@xxxxxxxxxxxx>
> > > Date:   Mon Nov 4 22:57:23 2019 +0000
> > >
> > >      uaccess: disallow > INT_MAX copy sizes
> >
> > Ah cool, this explains it.
> >
> > fwiw I never managed to get the WARNING in the backtrace to lign up
> > with any code. No idea what's been going on.
>
> Ok I think I have an idea, the above commit isn't in the linux-next I
> have here. Where is this from?
> -Daniel

You need to fetch tags to linux-next. syzbot started bisecting from
the commit where the crash happened, and it is now probably not the
current tag.

linux$ git show 9e5a64c71b2f70ba530f8156046dd7dfb8a7a0ba
commit 9e5a64c71b2f70ba530f8156046dd7dfb8a7a0ba
Author: Kees Cook <keescook@xxxxxxxxxxxx>
Date:   Tue Nov 5 09:57:23 2019 +1100

    uaccess: disallow > INT_MAX copy sizes

    As we've done with VFS, string operations, etc, reject usercopy sizes
    larger than INT_MAX, which would be nice to have for catching bugs related
    to size calculation overflows[1].

    This adds 10 bytes to x86_64 defconfig text and 1980 bytes to the data
    section:

       text    data     bss     dec     hex filename
    19691167        5134320 1646664 26472151        193eed7 vmlinux.before
    19691177        5136300 1646664 26474141        193f69d vmlinux.after

    [1] https://marc.info/?l=linux-s390&m=156631939010493&w=2

    Link: http://lkml.kernel.org/r/201908251612.F9902D7A@keescook
    Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Suggested-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
    Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 659a4400517b2..e93e249a4e9bf 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -147,6 +147,8 @@ check_copy_size(const void *addr, size_t bytes,
bool is_source)
                        __bad_copy_to();
                return false;
        }
+       if (WARN_ON_ONCE(bytes > INT_MAX))
+               return false;
        check_object_size(addr, bytes, is_source);
        return true;
 }


> > I'll type a patch to paper over this.
> > -Daniel
> >
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=125fe6dce00000
> > > start commit:   51309b9d Add linux-next specific files for 20191105
> > > git tree:       linux-next
> > > final crash:    https://syzkaller.appspot.com/x/report.txt?x=115fe6dce00000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=165fe6dce00000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=a9b1a641c1f1fc52
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=fb77e97ebf0612ee6914
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1212dc3ae00000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=145f604ae00000
> > >
> > > Reported-by: syzbot+fb77e97ebf0612ee6914@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Fixes: 9e5a64c71b2f ("uaccess: disallow > INT_MAX copy sizes")
> > >
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
> >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch