smbios: if a string value is unknown, use string number 0

The SMBIOS specification describes: "If a string field references no string,
a null (0) is placed in that string field."

Accordingly we should avoid writing a string "Unknown" to the SMBIOS table.

dmidecode displays 'Not Specified' if the string number is 0.

Commit 00a871d34e2f ("smbios: empty strings in smbios_add_string()")
correctly identified that strings may not have length 0 as two
consecutive NULs indentify the end of the string list. But the suggested
solution did not match the intent of the SMBIOS specification.

Fixes: 00a871d34e2f ("smbios: empty strings in smbios_add_string()")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

1 files changed, 18 insertions, 15 deletions

diff --git a/lib/smbios.c b/lib/smbios.c
index 0ae8578..6190c16 100644
--- a/lib/smbios.c
+++ b/lib/smbios.c
@@ -135,13 +135,16 @@ static const struct map_sysinfo *convert_sysinfo_to_dt(const char *node, const c
  *
  * @ctx:	SMBIOS context
  * @str:	string to add
- * Return:	string number in the string area (1 or more)
+ * Return:	string number in the string area. 0 if str is NULL.
  */
 static int smbios_add_string(struct smbios_ctx *ctx, const char *str)
 {
 	int i = 1;
 	char *p = ctx->eos;
 
+	if (!str)
+		return 0;
+
 	for (;;) {
 		if (!*p) {
 			ctx->last_str = p;
@@ -217,7 +220,7 @@ static int smbios_add_prop_si(struct smbios_ctx *ctx, const char *prop,
 	int ret;
 
 	if (!dval || !*dval)
-		dval = "Unknown";
+		dval = NULL;
 
 	if (!prop)
 		return smbios_add_string(ctx, dval);
@@ -380,19 +383,19 @@ static int smbios_write_type1(ulong *current, int handle,
 	memset(t, 0, sizeof(struct smbios_type1));
 	fill_smbios_header(t, SMBIOS_SYSTEM_INFORMATION, len, handle);
 	smbios_set_eos(ctx, t->eos);
-	t->manufacturer = smbios_add_prop(ctx, "manufacturer", "Unknown");
-	t->product_name = smbios_add_prop(ctx, "product", "Unknown");
+	t->manufacturer = smbios_add_prop(ctx, "manufacturer", NULL);
+	t->product_name = smbios_add_prop(ctx, "product", NULL);
 	t->version = smbios_add_prop_si(ctx, "version",
 					SYSINFO_ID_SMBIOS_SYSTEM_VERSION,
-					"Unknown");
+					NULL);
 	if (serial_str) {
 		t->serial_number = smbios_add_prop(ctx, NULL, serial_str);
 		strncpy((char *)t->uuid, serial_str, sizeof(t->uuid));
 	} else {
-		t->serial_number = smbios_add_prop(ctx, "serial", "Unknown");
+		t->serial_number = smbios_add_prop(ctx, "serial", NULL);
 	}
-	t->sku_number = smbios_add_prop(ctx, "sku", "Unknown");
-	t->family = smbios_add_prop(ctx, "family", "Unknown");
+	t->sku_number = smbios_add_prop(ctx, "sku", NULL);
+	t->family = smbios_add_prop(ctx, "family", NULL);
 
 	len = t->length + smbios_string_table_len(ctx);
 	*current += len;
@@ -411,12 +414,12 @@ static int smbios_write_type2(ulong *current, int handle,
 	memset(t, 0, sizeof(struct smbios_type2));
 	fill_smbios_header(t, SMBIOS_BOARD_INFORMATION, len, handle);
 	smbios_set_eos(ctx, t->eos);
-	t->manufacturer = smbios_add_prop(ctx, "manufacturer", "Unknown");
-	t->product_name = smbios_add_prop(ctx, "product", "Unknown");
+	t->manufacturer = smbios_add_prop(ctx, "manufacturer", NULL);
+	t->product_name = smbios_add_prop(ctx, "product", NULL);
 	t->version = smbios_add_prop_si(ctx, "version",
 					SYSINFO_ID_SMBIOS_BASEBOARD_VERSION,
-					"Unknown");
-	t->asset_tag_number = smbios_add_prop(ctx, "asset-tag", "Unknown");
+					NULL);
+	t->asset_tag_number = smbios_add_prop(ctx, "asset-tag", NULL);
 	t->feature_flags = SMBIOS_BOARD_FEATURE_HOSTING;
 	t->board_type = SMBIOS_BOARD_MOTHERBOARD;
 
@@ -437,7 +440,7 @@ static int smbios_write_type3(ulong *current, int handle,
 	memset(t, 0, sizeof(struct smbios_type3));
 	fill_smbios_header(t, SMBIOS_SYSTEM_ENCLOSURE, len, handle);
 	smbios_set_eos(ctx, t->eos);
-	t->manufacturer = smbios_add_prop(ctx, "manufacturer", "Unknown");
+	t->manufacturer = smbios_add_prop(ctx, "manufacturer", NULL);
 	t->chassis_type = SMBIOS_ENCLOSURE_DESKTOP;
 	t->bootup_state = SMBIOS_STATE_SAFE;
 	t->power_supply_state = SMBIOS_STATE_SAFE;
@@ -455,8 +458,8 @@ static void smbios_write_type4_dm(struct smbios_type4 *t,
 				  struct smbios_ctx *ctx)
 {
 	u16 processor_family = SMBIOS_PROCESSOR_FAMILY_UNKNOWN;
-	const char *vendor = "Unknown";
-	const char *name = "Unknown";
+	const char *vendor = NULL;
+	const char *name = NULL;
 
 #ifdef CONFIG_CPU
 	char processor_name[49];