Test rename[at] syscalls with absolute path (#22)

Check rename[at] doesn't unexpectedly require any rights for the
directory file descriptor if the path is an absolute path.

makefile

@@ -1,5 +1,5 @@
 all: capsicum-test smoketest mini-me mini-me.noexec mini-me.setuid $(EXTRA_PROGS)
-OBJECTS=capsicum-test-main.o capsicum-test.o capability-fd.o fexecve.o procdesc.o capmode.o fcntl.o ioctl.o openat.o sysctl.o select.o mqueue.o socket.o sctp.o capability-fd-pair.o linux.o overhead.o
+OBJECTS=capsicum-test-main.o capsicum-test.o capability-fd.o fexecve.o procdesc.o capmode.o fcntl.o ioctl.o openat.o sysctl.o select.o mqueue.o socket.o sctp.o capability-fd-pair.o linux.o overhead.o rename.o
 
 GTEST_DIR=gtest-1.6.0
 GTEST_INCS=-I$(GTEST_DIR)/include -I$(GTEST_DIR)

rename.cc

@@ -0,0 +1,49 @@
+#include <fcntl.h>
+#include <sys/stat.h>
+
+#include "./capsicum-test.h"
+
+// There was a Capsicum-related regression in FreeBSD renameat,
+// which affects certain cases independent of Capsicum or capability mode
+//
+// added to test the renameat syscall for the case that
+//    - the "to" file already exists
+//    - the "to" file is specified by an absolute path
+//    - the "to" file descriptor is used
+//          (this descriptor should be ignored if absolute path is provided)
+//
+// details at: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=222258
+
+
+const char * create_tmp_src(const char* filename) {
+    const char *src_path = TmpFile(filename);
+    int src_fd = open(src_path, O_CREAT|O_RDWR, 0644);
+    close(src_fd);
+    return src_path;
+}
+
+TEST(Rename, AbsDesignationSame) {
+    const char *src_path = create_tmp_src("rename_test");
+    EXPECT_OK(rename(src_path, src_path));
+    unlink(src_path);
+}
+
+TEST(RenameAt, AbsDesignationSame) {
+    const char *src_path = create_tmp_src("renameat_test");
+    const char *dir_path = TmpFile("renameat_test_dir");
+
+    EXPECT_OK(mkdir(dir_path, 0755));
+    // random temporary directory descriptor
+    int dfd = open(dir_path, O_DIRECTORY);
+
+    // Various rename from/to the same absolute path; in each case the source
+    // and dest directory FDs should be irrelevant.
+    EXPECT_OK(renameat(AT_FDCWD, src_path, AT_FDCWD, src_path));
+    EXPECT_OK(renameat(AT_FDCWD, src_path, dfd, src_path));
+    EXPECT_OK(renameat(dfd, src_path, AT_FDCWD, src_path));
+    EXPECT_OK(renameat(dfd, src_path, dfd, src_path));
+
+    close(dfd);
+    rmdir(dir_path);
+    unlink(src_path);
+}