efi_loader: Add size checks to efi_create_indexed_name()

Although the function description states the caller must provide a
sufficient buffer, it's better to have in function checks that the
destination buffer can hold the intended value.

So let's add an extra argument with the buffer size and check that
before doing any copying.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

include/efi_loader.h

@@ -824,7 +824,8 @@ bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp,
 void efi_memcpy_runtime(void *dest, const void *src, size_t n);
 
 /* commonly used helper function */
-u16 *efi_create_indexed_name(u16 *buffer, const char *name, unsigned int index);
+u16 *efi_create_indexed_name(u16 *buffer, size_t buffer_size, const char *name,
+			     unsigned int index);
 
 extern const struct efi_firmware_management_protocol efi_fmp_fit;
 extern const struct efi_firmware_management_protocol efi_fmp_raw;

lib/efi_loader/efi_capsule.c

@@ -73,8 +73,8 @@ void set_capsule_result(int index, struct efi_capsule_header *capsule,
 	struct efi_time time;
 	efi_status_t ret;
 
-	efi_create_indexed_name(variable_name16, "Capsule", index);
-
+	efi_create_indexed_name(variable_name16, sizeof(variable_name16),
+				"Capsule", index);
 	result.variable_total_size = sizeof(result);
 	result.capsule_guid = capsule->capsule_guid;
 	ret = EFI_CALL((*efi_runtime_services.get_time)(&time, NULL));
@@ -896,7 +896,8 @@ efi_status_t efi_launch_capsules(void)
 	free(files);
 
 	/* CapsuleLast */
-	efi_create_indexed_name(variable_name16, "Capsule", index - 1);
+	efi_create_indexed_name(variable_name16, sizeof(variable_name16),
+				"Capsule", index - 1);
 	efi_set_variable_int(L"CapsuleLast", &efi_guid_capsule_report,
 			     EFI_VARIABLE_READ_ONLY |
 			     EFI_VARIABLE_NON_VOLATILE |

lib/efi_loader/efi_string.c

@@ -23,13 +23,19 @@
  * Return: A pointer to the next position after the created string
  *	   in @buffer, or NULL otherwise
  */
-u16 *efi_create_indexed_name(u16 *buffer, const char *name, unsigned int index)
+u16 *efi_create_indexed_name(u16 *buffer, size_t buffer_size, const char *name,
+			     unsigned int index)
 {
 	u16 *p = buffer;
 	char index_buf[5];
+	size_t size;
 
+	size = (utf8_utf16_strlen(name) * sizeof(u16) +
+		sizeof(index_buf) * sizeof(u16));
+	if (buffer_size < size)
+		return NULL;
 	utf8_utf16_strcpy(&p, name);
-	sprintf(index_buf, "%04X", index);
+	snprintf(index_buf, sizeof(index_buf), "%04X", index);
 	utf8_utf16_strcpy(&p, index_buf);
 
 	return p;

test/unicode_ut.c

@@ -603,7 +603,7 @@ static int unicode_test_efi_create_indexed_name(struct unit_test_state *uts)
 	u16 *pos;
 
 	memset(buf, 0xeb, sizeof(buf));
-	pos = efi_create_indexed_name(buf, "Capsule", 0x0af9);
+	pos = efi_create_indexed_name(buf, sizeof(buf), "Capsule", 0x0af9);
 
 	ut_asserteq_mem(expected, buf, sizeof(expected));
 	ut_asserteq(pos - buf, u16_strnlen(buf, SIZE_MAX));