Fix seeding from random device w/o getrandom syscall

Use select to wait for /dev/random in readable state,
but do not actually read anything from /dev/random,
use /dev/urandom first.

Use linux define __NR_getrandom instead of the
glibc define SYS_getrandom, in case the kernel headers
are more current than the glibc headers.

Fixes openssl#8215

crypto/rand/rand_unix.c

@@ -19,7 +19,7 @@
 #include <stdio.h>
 #include "internal/dso.h"
 #if defined(__linux)
-# include <sys/syscall.h>
+# include <asm/unistd.h>
 #endif
 #if defined(__FreeBSD__)
 # include <sys/types.h>
@@ -324,8 +324,8 @@ static ssize_t syscall_random(void *buf, size_t buflen)
 #  endif
 
     /* Linux supports this since version 3.17 */
-#  if defined(__linux) && defined(SYS_getrandom)
-    return syscall(SYS_getrandom, buf, buflen, 0);
+#  if defined(__linux) && defined(__NR_getrandom)
+    return syscall(__NR_getrandom, buf, buflen, 0);
 #  elif (defined(__FreeBSD__) || defined(__NetBSD__)) && defined(KERN_ARND)
     return sysctl_random(buf, buflen);
 #  else
@@ -510,6 +510,24 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
     bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
     {
         size_t i;
+#ifdef DEVRANDOM_WAIT
+        static int wait_done = 0;
+
+        if (!wait_done && bytes_needed > 0) {
+             int f = open(DEVRANDOM_WAIT, O_RDONLY);
+
+             if (f >= 0) {
+                 fd_set fds;
+
+                 FD_ZERO(&fds);
+                 FD_SET(f, &fds);
+                 while (select(f+1, &fds, NULL, NULL, NULL) < 0
+                        && errno == EINTR);
+                 close(f);
+                 wait_done = 1;
+             }
+        }
+#endif
 
         for (i = 0; bytes_needed > 0 && i < OSSL_NELEM(random_device_paths); i++) {
             ssize_t bytes = 0;

e_os.h

@@ -27,11 +27,8 @@
  * set this to a comma-separated list of 'random' device files to try out. By
  * default, we will try to read at least one of these files
  */
-#  if defined(__s390__)
-#   define DEVRANDOM "/dev/prandom","/dev/urandom","/dev/hwrng","/dev/random"
-#  else
-#   define DEVRANDOM "/dev/urandom","/dev/random","/dev/srandom"
-#  endif
+#  define DEVRANDOM "/dev/urandom", "/dev/random","/dev/hwrng", "/dev/srandom"
+#  define DEVRANDOM_WAIT "/dev/random"
 # endif
 # if !defined(OPENSSL_NO_EGD) && !defined(DEVRANDOM_EGD)
 /*