1 files changed, 48 insertions, 0 deletions
diff --git a/include/linux/string.h b/include/linux/string.h
index 46e91d684c47..1cd63a8a23ab 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -6,6 +6,7 @@
 #include <linux/compiler.h>	/* for inline */
 #include <linux/types.h>	/* for size_t */
 #include <linux/stddef.h>	/* for NULL */
+#include <linux/errno.h>	/* for E2BIG */
 #include <stdarg.h>
 #include <uapi/linux/string.h>
 
@@ -357,6 +358,53 @@ __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size)
 	return ret;
 }
 
+/* defined after fortified strnlen to reuse it */
+extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy);
+__FORTIFY_INLINE ssize_t strscpy(char *p, const char *q, size_t size)
+{
+	size_t len;
+	/* Use string size rather than possible enclosing struct size. */
+	size_t p_size = __builtin_object_size(p, 1);
+	size_t q_size = __builtin_object_size(q, 1);
+
+	/* If we cannot get size of p and q default to call strscpy. */
+	if (p_size == (size_t) -1 && q_size == (size_t) -1)
+		return __real_strscpy(p, q, size);
+
+	/*
+	 * If size can be known at compile time and is greater than
+	 * p_size, generate a compile time write overflow error.
+	 */
+	if (__builtin_constant_p(size) && size > p_size)
+		__write_overflow();
+
+	/*
+	 * This call protects from read overflow, because len will default to q
+	 * length if it smaller than size.
+	 */
+	len = strnlen(q, size);
+	/*
+	 * If len equals size, we will copy only size bytes which leads to
+	 * -E2BIG being returned.
+	 * Otherwise we will copy len + 1 because of the final '\O'.
+	 */
+	len = len == size ? size : len + 1;
+
+	/*
+	 * Generate a runtime write overflow error if len is greater than
+	 * p_size.
+	 */
+	if (len > p_size)
+		fortify_panic(__func__);
+
+	/*
+	 * We can now safely call vanilla strscpy because we are protected from:
+	 * 1. Read overflow thanks to call to strnlen().
+	 * 2. Write overflow thanks to above ifs.
+	 */
+	return __real_strscpy(p, q, len);
+}
+
 /* defined after fortified strlen and strnlen to reuse them */
 __FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count)
 {