[PATCH] acpi: add null check on calls to get_space_id_name()

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

A null can be potentially returned from get_space_id_name() if the id is
out of range, so add a null check. Also don't call the function multiple
times but use a temporary char * pointer to stash the result of the call.

Addresses-Coverity: ("Dereference null return")
Fixes: ffea02df09d3 ("acpi: add fwts_acpi_space_id_check to check GAS adrress space ids")
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 src/lib/src/fwts_acpi_tables.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/lib/src/fwts_acpi_tables.c b/src/lib/src/fwts_acpi_tables.c
index 6ad1bf77..d832a65c 100644
--- a/src/lib/src/fwts_acpi_tables.c
+++ b/src/lib/src/fwts_acpi_tables.c
@@ -1668,17 +1668,23 @@ void fwts_acpi_space_id_check(
 
 	va_start(ap, num_type);
 	for (i = 0; i < num_type; i++) {
+		const char *id_name;
+
 		must_be = va_arg(ap, int);
 		if (actual == must_be) {
 			matched = true;
 			break;
 		}
 
-		length += strlen(get_space_id_name(must_be));
+		id_name = get_space_id_name(must_be);
+		if (!id_name)
+			continue;
+
+		length += strlen(id_name);
 		if (length > 255)
 			continue;
 
-		strncat(must_be_id, get_space_id_name(must_be), strlen(get_space_id_name(must_be)));
+		strncat(must_be_id, id_name, strlen(id_name));
 		if (i < num_type - 2)
 			strncat(must_be_id, ", ", 3);
 		else if (i == num_type - 2)
-- 
2.29.2