[PATCH v2] libselinux: use designated initializers for label initfuncs

["Thiébaud Weksteen" <tweek@google.com>]

Previously, the initfuncs array relied on implicit positional ordering
to match backend context constants (e.g., SELABEL_CTX_FILE). If constants
were reordered or added, array indexing could become misaligned.

Use C99 designated initializers in initfuncs to explicitly bind each
initialization function to its corresponding context constant.

Additionally, define _SELABEL_CTX_NUM in include/selinux/label.h
to count total backends, and add a compile-time static_assert ensuring
initfuncs stays in sync with _SELABEL_CTX_NUM.

Signed-off-by: Thiébaud Weksteen <tweek@google.com>
---
v2: Rebase on selinux/main and format

 libselinux/include/selinux/label.h |  5 +++++
 libselinux/src/label.c             | 18 ++++++++++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/libselinux/include/selinux/label.h b/libselinux/include/selinux/label.h
index 748b0db0..bde2501f 100644
--- a/libselinux/include/selinux/label.h
+++ b/libselinux/include/selinux/label.h
@@ -37,6 +37,11 @@ struct selabel_handle;
 #define SELABEL_CTX_ANDROID_PROP 4
 /* Android service contexts */
 #define SELABEL_CTX_ANDROID_SERVICE 5
+/*
+ * Total number of context backends. When adding a new backend,
+ * please increase this value.
+ */
+#define _SELABEL_CTX_NUM 6
 
 /*
  * Available options
diff --git a/libselinux/src/label.c b/libselinux/src/label.c
index 1ccd1abe..991b9769 100644
--- a/libselinux/src/label.c
+++ b/libselinux/src/label.c
@@ -4,6 +4,7 @@
  * Author : Eamon Walsh <ewalsh@epoch.ncsc.mil>
  */
 
+#include <assert.h>
 #include <sys/types.h>
 #include <ctype.h>
 #include <errno.h>
@@ -45,14 +46,19 @@ typedef int (*selabel_initfunc)(struct selabel_handle *rec,
 				const struct selinux_opt *opts, unsigned nopts);
 
 static const selabel_initfunc initfuncs[] = {
-	&selabel_file_init,
-	CONFIG_MEDIA_BACKEND(selabel_media_init),
-	CONFIG_X_BACKEND(selabel_x_init),
-	CONFIG_DB_BACKEND(selabel_db_init),
-	CONFIG_ANDROID_BACKEND(selabel_property_init),
-	CONFIG_ANDROID_BACKEND(selabel_service_init),
+	[SELABEL_CTX_FILE] = &selabel_file_init,
+	[SELABEL_CTX_MEDIA] = CONFIG_MEDIA_BACKEND(selabel_media_init),
+	[SELABEL_CTX_X] = CONFIG_X_BACKEND(selabel_x_init),
+	[SELABEL_CTX_DB] = CONFIG_DB_BACKEND(selabel_db_init),
+	[SELABEL_CTX_ANDROID_PROP] =
+		CONFIG_ANDROID_BACKEND(selabel_property_init),
+	[SELABEL_CTX_ANDROID_SERVICE] =
+		CONFIG_ANDROID_BACKEND(selabel_service_init),
 };
 
+static_assert(ARRAY_SIZE(initfuncs) == _SELABEL_CTX_NUM,
+	      "initfuncs array size does not match _SELABEL_CTX_NUM");
+
 static inline struct selabel_digest *
 selabel_is_digest_set(const struct selinux_opt *opts, unsigned n)
 {
-- 
2.55.0.229.g6434b31f56-goog