Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Mon, 6 Feb 2023 21:03:19 +0100 | Subject | Re: [PATCH] uaccess: Add minimum bounds check on kernel buffer size |
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Hi Arnd,
On Fri, Feb 3, 2023 at 10:23 PM Arnd Bergmann <arnd@arndb.de> wrote: > On Fri, Feb 3, 2023, at 20:35, Kees Cook wrote: > > --- a/include/linux/uaccess.h > > +++ b/include/linux/uaccess.h > > @@ -329,6 +329,10 @@ copy_struct_from_user(void *dst, size_t ksize, > > const void __user *src, > > size_t size = min(ksize, usize); > > size_t rest = max(ksize, usize) - size; > > > > + /* Double check if ksize is larger than a known object size. */ > > + if (WARN_ON_ONCE(ksize > __builtin_object_size(dst, 1))) > > + return -E2BIG; > > + > > WARN_ON_ONCE() may be a little expensive since that adds two > comparisons and a static variable to each copy, but it's probably > fine.
When seeing this, I was a bit worried about the size increase. Hence I gave it a try on atari_defconfig and ran bloat-o-meter. Surprisingly, there was no size increase at all, as all checks were optimized away.
Hence perhaps this can become a compile-time check?
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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