[LTP] [PATCH v3 3/3] safe_semctl: Fix undefined behaviour in vararg handling

[Tudor Cretu]

Accessing elements in an empty va_list is undefined behaviour.
The semctl system call expects the union semun argument only for a
set of cmd values, otherwise the argument is ignored.

Modify the safe_semctl wrapper to read the variadic argument only when
it's expected to be provided.

Signed-off-by: Tudor Cretu <tudor.cretu@arm.com>
---
 include/lapi/ipc.h      | 14 ++++++++++++++
 lib/tst_safe_sysv_ipc.c | 23 ++++++++++++++++-------
 2 files changed, 30 insertions(+), 7 deletions(-)
 create mode 100644 include/lapi/ipc.h

diff --git a/include/lapi/ipc.h b/include/lapi/ipc.h
new file mode 100644
index 000000000..5645c8817
--- /dev/null
+++ b/include/lapi/ipc.h
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2022 Arm Ltd.
+ */
+#ifndef LAPI_IPC_H__
+#define LAPI_IPC_H__
+
+#include <sys/ipc.h>
+
+#ifndef IPC_INFO
+# define IPC_INFO 3
+#endif
+
+#endif /* LAPI_IPC_H__ */
diff --git a/lib/tst_safe_sysv_ipc.c b/lib/tst_safe_sysv_ipc.c
index 5eaa82539..a196fc9ce 100644
--- a/lib/tst_safe_sysv_ipc.c
+++ b/lib/tst_safe_sysv_ipc.c
@@ -4,12 +4,12 @@
  */
 
 #include <sys/types.h>
-#include <sys/ipc.h>
 #include <sys/msg.h>
 #include <sys/shm.h>
 #define TST_NO_DEFAULT_MAIN
 #include "tst_test.h"
 #include "tst_safe_sysv_ipc.h"
+#include "lapi/ipc.h"
 #include "lapi/sem.h"
 
 /*
@@ -232,13 +232,22 @@ int safe_semctl(const char *file, const int lineno, int semid, int semnum,
 {
 	int rval;
 	va_list va;
-	union semun un;
+	union semun un = {0};
 
-	va_start(va, cmd);
-
-	un = va_arg(va, union semun);
-
-	va_end(va);
+	switch (cmd) {
+	case SETVAL:
+	case GETALL:
+	case SETALL:
+	case IPC_STAT:
+	case IPC_SET:
+	case SEM_STAT:
+	case SEM_STAT_ANY:
+	case IPC_INFO:
+	case SEM_INFO:
+		va_start(va, cmd);
+		un = va_arg(va, union semun);
+		va_end(va);
+	}
 
 	rval = semctl(semid, semnum, cmd, un);
 
-- 
2.25.1