[PATCH 5.14 363/849] fortify: Fix dropped strcpy() compile-time write overflow check

[Greg Kroah-Hartman]

From: Kees Cook <keescook@xxxxxxxxxxxx>

[ Upstream commit 072af0c638dc8a5c7db2edc4dddbd6d44bee3bdb ]

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@xxxxxxxxxx>
Cc: Francis Laniel <laniel_francis@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 c1be37437e778..0c70febd03e95 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -280,7 +280,10 @@ __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);
-- 
2.33.0