From: Mark Rutland <mark.rutland@xxxxxxx> Subject: lib: harden strncpy_from_user The strncpy_from_user() accessor is effectively a copy_from_user() specialised to copy strings, terminating early at a NUL byte if possible. In other respects it is identical, and can be used to copy an arbitrarily large buffer from userspace into the kernel. Conceptually, it exposes a similar attack surface. As with copy_from_user(), we check the destination range when the kernel is built with KASAN, but unlike copy_from_user() we do not check the destination buffer when using HARDENED_USERCOPY. As strncpy_from_user() calls get_user() in a loop, we must call check_object_size() explicitly. This patch adds this instrumentation to strncpy_from_user(), per the same rationale as with the regular copy_from_user(). In the absence of hardened usercopy this will have no impact as the instrumentation expands to an empty static inline function. Link: http://lkml.kernel.org/r/1472221903-31181-1-git-send-email-mark.rutland@xxxxxxx Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/strncpy_from_user.c | 2 ++ 1 file changed, 2 insertions(+) diff -puN lib/strncpy_from_user.c~lib-harden-strncpy_from_user lib/strncpy_from_user.c --- a/lib/strncpy_from_user.c~lib-harden-strncpy_from_user +++ a/lib/strncpy_from_user.c @@ -1,6 +1,7 @@ #include <linux/compiler.h> #include <linux/export.h> #include <linux/kasan-checks.h> +#include <linux/thread_info.h> #include <linux/uaccess.h> #include <linux/kernel.h> #include <linux/errno.h> @@ -111,6 +112,7 @@ long strncpy_from_user(char *dst, const long retval; kasan_check_write(dst, count); + check_object_size(dst, count, false); user_access_begin(); retval = do_strncpy_from_user(dst, src, count, max); user_access_end(); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
