1 files changed, 73 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/getentropy.c b/sysdeps/unix/sysv/linux/getentropy.c
new file mode 100644
index 0000000000..561f8f4c7c
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/getentropy.c
@@ -0,0 +1,73 @@
+/* Implementation of getentropy based on the getrandom system call.
+   Copyright (C) 2016-2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sys/random.h>
+#include <assert.h>
+#include <errno.h>
+#include <unistd.h>
+
+#ifdef __NR_getrandom
+/* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
+   success and -1 on failure.  */
+int
+getentropy (void *buffer, size_t length)
+{
+  /* The interface is documented to return EIO for buffer lengths
+     longer than 256 bytes.  */
+  if (length > 256)
+    {
+      __set_errno (EIO);
+      return -1;
+    }
+
+  /* Try to fill the buffer completely.  Even with the 256 byte limit
+     above, we might still receive an EINTR error (when blocking
+     during boot).  */
+  void *end = buffer + length;
+  while (buffer < end)
+    {
+      /* NB: No cancellation point.  */
+      ssize_t bytes = INLINE_SYSCALL_CALL (getrandom, buffer, end - buffer, 0);
+      if (bytes < 0)
+        {
+          if (errno == EINTR)
+            /* Try again if interrupted by a signal.  */
+            continue;
+          else
+            return -1;
+        }
+      if (bytes == 0)
+        {
+          /* No more bytes available.  This should not happen under
+             normal circumstances.  */
+          __set_errno (EIO);
+          return -1;
+        }
+      /* Try again in case of a short read.  */
+      buffer += bytes;
+    }
+  return 0;
+}
+#else
+int
+getentropy (void *buffer, size_t length)
+{
+  __set_errno (ENOSYS);
+  return -1;
+}
+#endif