libc: Add O_PATH support for fgetxattr / fsetxattr

Support O_PATH file descriptors when handling fgetxattr and fsetxattr.
This avoids requiring file read access to pull extended attributes.

This is needed to support O_PATH file descriptors when calling
SELinux's fgetfilecon() call. In particular, this allows the querying
and setting of SELinux file context by using something like the following
code:

  int dirfd = open("/path/to/dir", O_DIRECTORY);
  int fd = openat(dirfd, "file", O_PATH | O_NOFOLLOW);
  char *context;
  fgetfilecon(fd, &context);

This change was motivated by a comment in
https://android-review.googlesource.com/#/c/152680/1/toys/posix/ls.c

(cherrypicked from commit 2825f10b7f61558c264231a536cf3affc0d84204)

Change-Id: Ic0cdf9f9dd0e35a63b44a4c4a08400020041eddf

2 files changed, 101 insertions, 0 deletions

diff --git a/tests/Android.mk b/tests/Android.mk
index 0f3454c..37f7b4f 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -107,6 +107,7 @@ libBionicStandardTests_src_files := \
     sys_time_test.cpp \
     sys_types_test.cpp \
     sys_vfs_test.cpp \
+    sys_xattr_test.cpp \
     system_properties_test.cpp \
     time_test.cpp \
     uchar_test.cpp \
diff --git a/tests/sys_xattr_test.cpp b/tests/sys_xattr_test.cpp
new file mode 100644
index 0000000..1842682
--- /dev/null
+++ b/tests/sys_xattr_test.cpp
@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include <sys/types.h>
+#include <sys/xattr.h>
+
+#include "TemporaryFile.h"
+
+TEST(sys_xattr, setxattr) {
+  TemporaryFile tf;
+  char buf[10];
+  ASSERT_EQ(0, setxattr(tf.filename, "user.foo", "bar", 4, 0));
+  ASSERT_EQ(4, getxattr(tf.filename, "user.foo", buf, sizeof(buf)));
+  ASSERT_STREQ("bar", buf);
+  buf[0] = '\0';
+  ASSERT_EQ(4, lgetxattr(tf.filename, "user.foo", buf, sizeof(buf)));
+  ASSERT_STREQ("bar", buf);
+}
+
+TEST(sys_xattr, fsetxattr) {
+  TemporaryFile tf;
+  char buf[10];
+  ASSERT_EQ(0, fsetxattr(tf.fd, "user.foo", "bar", 4, 0));
+  ASSERT_EQ(4, fgetxattr(tf.fd, "user.foo", buf, sizeof(buf)));
+  ASSERT_STREQ("bar", buf);
+}
+
+TEST(sys_xattr, fsetxattr_zerobuf) {
+  TemporaryFile tf;
+  char buf[10];
+  ASSERT_EQ(0, fsetxattr(tf.fd, "user.foo", "", 0, 0));
+  ASSERT_EQ(0, fgetxattr(tf.fd, "user.foo", buf, sizeof(buf)));
+}
+
+TEST(sys_xattr, fsetxattr_toosmallbuf) {
+  TemporaryFile tf;
+  char buf[10];
+  ASSERT_EQ(0, fsetxattr(tf.fd, "user.foo", "01234567890123456789", 21, 0));
+  ASSERT_EQ(-1, fgetxattr(tf.fd, "user.foo", buf, sizeof(buf)));
+  ASSERT_EQ(ERANGE, errno);
+}
+
+TEST(sys_xattr, fsetxattr_invalidfd) {
+  char buf[10];
+  errno = 0;
+  ASSERT_EQ(-1, fsetxattr(65535, "user.foo", "0123", 5, 0));
+  ASSERT_EQ(EBADF, errno);
+  errno = 0;
+  ASSERT_EQ(-1, fgetxattr(65535, "user.foo", buf, sizeof(buf)));
+  ASSERT_EQ(EBADF, errno);
+}
+
+TEST(sys_xattr, fsetxattr_with_opath) {
+  TemporaryFile tf;
+  int fd = open(tf.filename, O_PATH);
+  ASSERT_NE(-1, fd);
+
+  int res = fsetxattr(fd, "user.foo", "bar", 4, 0);
+#if defined(__BIONIC__)
+  char buf[10];
+  ASSERT_EQ(0, res);
+  ASSERT_EQ(4, fgetxattr(fd, "user.foo", buf, sizeof(buf)));
+  ASSERT_STREQ("bar", buf);
+#else
+  ASSERT_EQ(-1, res);
+  ASSERT_EQ(EBADF, errno);
+#endif
+}
+
+TEST(sys_xattr, fsetxattr_with_opath_toosmall) {
+  TemporaryFile tf;
+  int fd = open(tf.filename, O_PATH);
+  ASSERT_NE(-1, fd);
+
+  int res = fsetxattr(fd, "user.foo", "01234567890123456789", 21, 0);
+#if defined(__BIONIC__)
+  char buf[10];
+  ASSERT_EQ(0, res);
+  ASSERT_EQ(-1, fgetxattr(fd, "user.foo", buf, sizeof(buf)));
+  ASSERT_EQ(ERANGE, errno);
+#else
+  ASSERT_EQ(-1, res);
+  ASSERT_EQ(EBADF, errno);
+#endif
+}