Messages in this thread | | | Date | Wed, 8 Feb 2023 16:48:18 +1100 | From | Aleksa Sarai <> | Subject | Re: [PATCH] uaccess: Add minimum bounds check on kernel buffer size |
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On 2023-02-03, Kees Cook <keescook@chromium.org> wrote: > While there is logic about the difference between ksize and usize, > copy_struct_from_user() didn't check the size of the destination buffer > (when it was known) against ksize. Add this check so there is an upper > bounds check on the possible memset() call, otherwise lower bounds > checks made by callers will trigger bounds warnings under -Warray-bounds. > Seen under GCC 13: > > In function 'copy_struct_from_user', > inlined from 'iommufd_fops_ioctl' at > ../drivers/iommu/iommufd/main.c:333:8: > ../include/linux/fortify-string.h:59:33: warning: '__builtin_memset' offset [57, 4294967294] is out of the bounds [0, 56] of object 'buf' with type 'union ucmd_buffer' [-Warray-bounds=] > 59 | #define __underlying_memset __builtin_memset > | ^ > ../include/linux/fortify-string.h:453:9: note: in expansion of macro '__underlying_memset' > 453 | __underlying_memset(p, c, __fortify_size); \ > | ^~~~~~~~~~~~~~~~~~~ > ../include/linux/fortify-string.h:461:25: note: in expansion of macro '__fortify_memset_chk' > 461 | #define memset(p, c, s) __fortify_memset_chk(p, c, s, \ > | ^~~~~~~~~~~~~~~~~~~~ > ../include/linux/uaccess.h:334:17: note: in expansion of macro 'memset' > 334 | memset(dst + size, 0, rest); > | ^~~~~~ > ../drivers/iommu/iommufd/main.c: In function 'iommufd_fops_ioctl': > ../drivers/iommu/iommufd/main.c:311:27: note: 'buf' declared here > 311 | union ucmd_buffer buf; > | ^~~
Makes sense.
Acked-by: Aleksa Sarai <cyphar@cyphar.com>
> > Cc: Aleksa Sarai <cyphar@cyphar.com> > Cc: Christian Brauner <christian.brauner@ubuntu.com> > Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Dinh Nguyen <dinguyen@kernel.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Geert Uytterhoeven <geert@linux-m68k.org> > Cc: Alexander Potapenko <glider@google.com> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > include/linux/uaccess.h | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h > index afb18f198843..ab9728138ad6 100644 > --- 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; > + > /* Deal with trailing bytes. */ > if (usize < ksize) { > memset(dst + size, 0, rest); > -- > 2.34.1 >
-- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/> [unhandled content-type:application/pgp-signature] | |