1 files changed, 67 insertions, 0 deletions
diff --git a/libc/bionic/fchmodat.cpp b/libc/bionic/fchmodat.cpp
new file mode 100644
index 000000000..c28e15ac7
--- /dev/null
+++ b/libc/bionic/fchmodat.cpp
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <unistd.h>
+
+#include "private/ErrnoRestorer.h"
+
+extern "C" int __fchmodat(int, const char*, mode_t);
+
+int fchmodat(int dirfd, const char* pathname, mode_t mode, int flags) {
+  if ((flags & ~AT_SYMLINK_NOFOLLOW) != 0) {
+    errno = EINVAL;
+    return -1;
+  }
+
+  if (flags & AT_SYMLINK_NOFOLLOW) {
+    // Emulate AT_SYMLINK_NOFOLLOW using the mechanism described
+    // at https://sourceware.org/bugzilla/show_bug.cgi?id=14578
+    // comment #10
+
+    int fd = openat(dirfd, pathname, O_PATH | O_NOFOLLOW | O_CLOEXEC);
+    if (fd == -1) {
+      return -1; // returns errno from openat
+    }
+
+    // POSIX requires that ENOTSUP be returned when the system
+    // doesn't support setting the mode of a symbolic link.
+    // This is true for all Linux kernels.
+    // We rely on the O_PATH compatibility layer added in the
+    // fchmod() function to get errno correct.
+    int result = fchmod(fd, mode);
+    ErrnoRestorer errno_restorer; // don't let close() clobber errno
+    close(fd);
+    return result;
+  }
+
+  return __fchmodat(dirfd, pathname, mode);
+}