android/sync: use get_unused_fd_flags(O_CLOEXEC) instead of get_unused_fd()

Macro get_unused_fd() is used to allocate a file descriptor with
default flags. Those default flags (0) can be "unsafe":
O_CLOEXEC must be used by default to not leak file descriptor
across exec().

Instead of macro get_unused_fd(), functions anon_inode_getfd()
or get_unused_fd_flags() should be used with flags given by userspace.
If not possible, flags should be set to O_CLOEXEC to provide userspace
with a default safe behavor.

In a further patch, get_unused_fd() will be removed so that
new code start using anon_inode_getfd() or get_unused_fd_flags()
with correct flags.

This patch replaces calls to get_unused_fd() with call to
get_unused_fd_flags(O_CLOEXEC) following advice from Erik Gilling.
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Cc: Erik Gilling <konkers@android.com>
Cc: Colin Cross <ccross@google.com>
Link: http://lkml.kernel.org/r/CACSP8SjXGMk2_kX_+RgzqqQwqKernvF1Wt3K5tw991W5dfAnCA@mail.gmail.com
Link: http://lkml.kernel.org/r/cover.1376327678.git.ydroneaud@opteya.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/sync.c

@@ -697,7 +697,7 @@ static long sync_fence_ioctl_wait(struct sync_fence *fence, unsigned long arg)
 
 static long sync_fence_ioctl_merge(struct sync_fence *fence, unsigned long arg)
 {
-	int fd = get_unused_fd();
+	int fd = get_unused_fd_flags(O_CLOEXEC);
 	int err;
 	struct sync_fence *fence2, *fence3;
 	struct sync_merge_data data;