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uaccess: Add minimum bounds check on kernel buffer size

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[ Upstream commit 04ffde1319 ]

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;
      |                           ^~~

Cc: Christian Brauner <brauner@kernel.org>
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>
Acked-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/lkml/20230203193523.never.667-kees@kernel.org/
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Kees Cook 2023-01-31 17:37:59 -08:00 • committed by Justin Hammond
parent 37c051ce5b
commit ec06172223
1 changed files with 4 additions and 0 deletions
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4
include/linux/uaccess.h
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@ -338,6 +338,10 @@ 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);