From 04ffde1319a715bd0550ded3580d4ea3bc003776 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 31 Jan 2023 17:37:59 -0800 Subject: [PATCH] uaccess: Add minimum bounds check on kernel buffer size 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 Cc: Rasmus Villemoes Cc: Arnd Bergmann Cc: Dinh Nguyen Cc: Catalin Marinas Cc: Andrew Morton Cc: Geert Uytterhoeven Cc: Alexander Potapenko Acked-by: Aleksa Sarai Signed-off-by: Kees Cook Link: https://lore.kernel.org/lkml/20230203193523.never.667-kees@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 afb18f1..ab97281 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); -- 2.7.4