From 7159864c6ed301f5c3208e6c5b653f42d3b72c1e 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 [ Upstream commit bbe0ec34738dda22d93ebc66e83d0db49516218d ] 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/ Signed-off-by: Sasha Levin --- include/linux/uaccess.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index afb18f198843b..ab9728138ad67 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); -- 2.39.5