[PATCH userspace v4 5/8] libselinux: make is_context_customizable() thread-safe

[Ondrej Mosnacek <omosnace@xxxxxxxxxx>]

Use the __selinux_once() macro to ensure that threads don't race to
initialize the list of customizable types.

Reported-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
 libselinux/src/is_customizable_type.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/libselinux/src/is_customizable_type.c b/libselinux/src/is_customizable_type.c
index 1b17860c..f83e1e83 100644
--- a/libselinux/src/is_customizable_type.c
+++ b/libselinux/src/is_customizable_type.c
@@ -9,7 +9,10 @@
 #include "selinux_internal.h"
 #include "context_internal.h"
 
-static int get_customizable_type_list(char *** retlist)
+static char **customizable_list = NULL;
+static pthread_once_t customizable_once = PTHREAD_ONCE_INIT;
+
+static void customizable_init(void)
 {
 	FILE *fp;
 	char *buf;
@@ -18,12 +21,12 @@ static int get_customizable_type_list(char *** retlist)
 
 	fp = fopen(selinux_customizable_types_path(), "re");
 	if (!fp)
-		return -1;
+		return;
 
 	buf = malloc(selinux_page_size);
 	if (!buf) {
 		fclose(fp);
-		return -1;
+		return;
 	}
 	while (fgets_unlocked(buf, selinux_page_size, fp) && ctr < UINT_MAX) {
 		ctr++;
@@ -54,23 +57,19 @@ static int get_customizable_type_list(char *** retlist)
 	fclose(fp);
 	free(buf);
 	if (!list)
-		return -1;
-	*retlist = list;
-	return 0;
+		return;
+	customizable_list = list;
 }
 
-static char **customizable_list = NULL;
-
 int is_context_customizable(const char * scontext)
 {
 	int i;
 	const char *type;
 	context_t c;
 
-	if (!customizable_list) {
-		if (get_customizable_type_list(&customizable_list) != 0)
-			return -1;
-	}
+	__selinux_once(customizable_once, customizable_init);
+	if (!customizable_list)
+		return -1;
 
 	c = context_new(scontext);
 	if (!c)
-- 
2.31.1