avoid invalid use of va_arg in open

reading the variadic mode argument is only valid when the O_CREAT flag
is present. this probably does not matter, but is needed for formal
correctness, and could affect LTO or other full-program analysis.

diff --git a/src/fcntl/open.c b/src/fcntl/open.c
index 088a28f74b6212cd9bd9ec2083d1245abf7e989d..5e5be1d7b483aecf325123c954afb28cca15ea19 100644 (file)
--- a/src/fcntl/open.c
+++ b/src/fcntl/open.c
@@ -5,11 +5,14 @@
 
 int open(const char *filename, int flags, ...)
 {
-       mode_t mode;
-       va_list ap;
-       va_start(ap, flags);
-       mode = va_arg(ap, mode_t);
-       va_end(ap);
+       mode_t mode = 0;
+
+       if (flags & O_CREAT) {
+               va_list ap;
+               va_start(ap, flags);
+               mode = va_arg(ap, mode_t);
+               va_end(ap);
+       }
 
        int fd = __sys_open_cp(filename, flags, mode);
        if (fd>=0 && (flags & O_CLOEXEC))