From: Kees Cook keescook@chromium.org
[ Upstream commit 04ffde1319a715bd0550ded3580d4ea3bc003776 ]
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 --- include/linux/uaccess.h | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index c7c6e8b8344d4..20668760daa02 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -348,6 +348,10 @@ 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);