[PATCH v2 29/63] fortify: Fix dropped strcpy() compile-time write overflow check

[Kees Cook]

The implementation for intra-object overflow in str*-family functions
accidentally dropped compile-time write overflow checking in strcpy(),
leaving it entirely to run-time. Add back the intended check.

Fixes: 6a39e62abbaf ("lib: string.h: detect intra-object overflow in fortified string functions")
Cc: Daniel Axtens <dja at axtens.net>
Cc: Francis Laniel <laniel_francis at privacyrequired.com>
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 include/linux/fortify-string.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 7e67d02764db..68bc5978d916 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -287,7 +287,10 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q)
 	if (p_size == (size_t)-1 && q_size == (size_t)-1)
 		return __underlying_strcpy(p, q);
 	size = strlen(q) + 1;
-	/* test here to use the more stringent object size */
+	/* Compile-time check for const size overflow. */
+	if (__builtin_constant_p(size) && p_size < size)
+		__write_overflow();
+	/* Run-time check for dynamic size overflow. */
 	if (p_size < size)
 		fortify_panic(__func__);
 	memcpy(p, q, size);
-- 
2.30.2