[LTP] [PATCH v2 2/3] safe_openat: Fix undefined behaviour in vararg handling

[Tudor Cretu]

Accessing elements in an empty va_list is undefined behaviour.
Therefore, remove the variadicness from safe_openat as it always calls
openat with the mode argument included.

Adapt the SAFE_OPENAT macro to handle the change by passing a default
argument of 0 to mode if it's omitted.

Signed-off-by: Tudor Cretu <tudor.cretu@arm.com>
---
 include/tst_safe_file_at.h | 10 ++++++----
 lib/tst_cgroup.c           |  2 +-
 lib/tst_safe_file_at.c     | 11 +++--------
 3 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/include/tst_safe_file_at.h b/include/tst_safe_file_at.h
index a1aa19fad..dd43d8f65 100644
--- a/include/tst_safe_file_at.h
+++ b/include/tst_safe_file_at.h
@@ -11,9 +11,11 @@
 #include <unistd.h>
 #include <stdarg.h>
 
-#define SAFE_OPENAT(dirfd, path, oflags, ...)			\
-	safe_openat(__FILE__, __LINE__,				\
-		    (dirfd), (path), (oflags), ## __VA_ARGS__)
+#define __SAFE_OPENAT(dirfd, path, oflags, mode, ...)			\
+	safe_openat(__FILE__, __LINE__, (dirfd), (path), (oflags), (mode))
+
+#define SAFE_OPENAT(dirfd, path, oflags, ...)				\
+	__SAFE_OPENAT((dirfd), (path), (oflags), ##__VA_ARGS__, 0)
 
 #define SAFE_FILE_READAT(dirfd, path, buf, nbyte)			\
 	safe_file_readat(__FILE__, __LINE__,				\
@@ -38,7 +40,7 @@ const char *tst_decode_fd(const int fd)
 			  __attribute__((warn_unused_result));
 
 int safe_openat(const char *const file, const int lineno, const int dirfd,
-                const char *const path, const int oflags, ...)
+                const char *const path, const int oflags, const mode_t mode)
 		__attribute__((nonnull, warn_unused_result));
 
 ssize_t safe_file_readat(const char *const file, const int lineno,
diff --git a/lib/tst_cgroup.c b/lib/tst_cgroup.c
index 50699bc63..9831bc336 100644
--- a/lib/tst_cgroup.c
+++ b/lib/tst_cgroup.c
@@ -1345,7 +1345,7 @@ int safe_cg_open(const char *const file, const int lineno,
 		if (!alias)
 			continue;
 
-		fds[i++] = safe_openat(file, lineno, (*dir)->dir_fd, alias, flags);
+		fds[i++] = safe_openat(file, lineno, (*dir)->dir_fd, alias, flags, 0);
 	}
 
 	return i;
diff --git a/lib/tst_safe_file_at.c b/lib/tst_safe_file_at.c
index f530dc349..9b8944f01 100644
--- a/lib/tst_safe_file_at.c
+++ b/lib/tst_safe_file_at.c
@@ -33,15 +33,10 @@ const char *tst_decode_fd(const int fd)
 }
 
 int safe_openat(const char *const file, const int lineno,
-		const int dirfd, const char *const path, const int oflags, ...)
+		const int dirfd, const char *const path, const int oflags,
+		const mode_t mode)
 {
-	va_list ap;
 	int fd;
-	mode_t mode;
-
-	va_start(ap, oflags);
-	mode = va_arg(ap, int);
-	va_end(ap);
 
 	fd = openat(dirfd, path, oflags, mode);
 	if (fd > -1)
@@ -58,7 +53,7 @@ ssize_t safe_file_readat(const char *const file, const int lineno,
 			 const int dirfd, const char *const path,
 			 char *const buf, const size_t nbyte)
 {
-	int fd = safe_openat(file, lineno, dirfd, path, O_RDONLY);
+	int fd = safe_openat(file, lineno, dirfd, path, O_RDONLY, 0);
 	ssize_t rval;
 
 	if (fd < 0)
-- 
2.25.1