1 files changed, 72 insertions, 0 deletions
diff --git a/libc/bionic/fchmod.cpp b/libc/bionic/fchmod.cpp
new file mode 100644
index 000000000..ace8c6b47
--- /dev/null
+++ b/libc/bionic/fchmod.cpp
@@ -0,0 +1,72 @@
+/*
+ * 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 <stdio.h>
+
+extern "C" int ___fchmod(int, mode_t);
+
+int fchmod(int fd, mode_t mode) {
+  int saved_errno = errno;
+  int result = ___fchmod(fd, mode);
+
+  if ((result == 0) || (errno != EBADF)) {
+    return result;
+  }
+
+  // fd could be an O_PATH file descriptor, and the kernel
+  // may not directly support fchmod() on such a file descriptor.
+  // Use /proc/self/fd instead to emulate this support.
+  // https://sourceware.org/bugzilla/show_bug.cgi?id=14578
+  //
+  // As of February 2015, there are no kernels which support fchmod
+  // on an O_PATH file descriptor, and "man open" documents fchmod
+  // on O_PATH file descriptors as returning EBADF.
+  int fd_flag = fcntl(fd, F_GETFL);
+  if ((fd_flag == -1) || ((fd_flag & O_PATH) == 0)) {
+    errno = EBADF;
+    return -1;
+  }
+
+  char buf[40];
+  snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fd);
+  errno = saved_errno;
+  result = chmod(buf, mode);
+  if ((result == -1) && (errno == ELOOP)) {
+    // Linux does not support changing the mode of a symlink.
+    // For fchmodat(AT_SYMLINK_NOFOLLOW), POSIX requires a return
+    // value of ENOTSUP. Assume that's true here too.
+    errno = ENOTSUP;
+  }
+
+  return result;
+}