Switch Linux getrandom() usage to non-blocking mode, continuing to

use fallback mechanims if unsuccessful.

The design of Linux getrandom is broken.  It has an
uninitialized phase coupled with blocking behaviour, which
is unacceptable from within a library at boot time without
possible recovery.
ok deraadt@ jsing@

1 files changed, 9 insertions, 6 deletions

diff --git a/src/lib/libcrypto/arc4random/getentropy_linux.c b/src/lib/libcrypto/arc4random/getentropy_linux.c
index ac97658efe..a845239eb3 100644
--- a/src/lib/libcrypto/arc4random/getentropy_linux.c
+++ b/src/lib/libcrypto/arc4random/getentropy_linux.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: getentropy_linux.c,v 1.43 2016/08/07 03:27:21 tb Exp $        */
+/*      $OpenBSD: getentropy_linux.c,v 1.44 2017/04/29 18:43:31 beck Exp $      */
 
 /*
  * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
@@ -96,13 +96,16 @@ getentropy(void *buf, size_t len)
 
 #ifdef SYS_getrandom
         /*
-         * Try descriptor-less getrandom()
+         * Try descriptor-less getrandom(), in non-blocking mode.
+         *
+         * The design of Linux getrandom is broken.  It has an
+         * uninitialized phase coupled with blocking behaviour, which
+         * is unacceptable from within a library at boot time without
+         * possible recovery. See http://bugs.python.org/issue26839#msg267745
          */
         ret = getentropy_getrandom(buf, len);
         if (ret != -1)
                 return (ret);
-        if (errno != ENOSYS)
-                return (-1);
 #endif
 
         /*
@@ -156,7 +159,7 @@ getentropy(void *buf, size_t len)
          *     - Do the best under the circumstances....
          *
          * This code path exists to bring light to the issue that Linux
-         * does not provide a failsafe API for entropy collection.
+         * still does not provide a failsafe API for entropy collection.
          *
          * We hope this demonstrates that Linux should either retain their
          * sysctl ABI, or consider providing a new failsafe API which
@@ -199,7 +202,7 @@ getentropy_getrandom(void *buf, size_t len)
         if (len > 256)
                 return (-1);
         do {
-                ret = syscall(SYS_getrandom, buf, len, 0);
+                ret = syscall(SYS_getrandom, buf, len, GRND_NONBLOCK);
         } while (ret == -1 && errno == EINTR);
 
         if (ret != len)