From 144c9852279ef0219c72fe549f72a40f3a255edc Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Wed, 29 May 2019 16:00:35 +0200
Subject: [PATCH] Handle short reads from our random device

Reported by Coverity (CID 1401626).
---
 pdns/dns_random.cc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/pdns/dns_random.cc b/pdns/dns_random.cc
index bb6e8e615..e2b8e4575 100644
--- a/pdns/dns_random.cc
+++ b/pdns/dns_random.cc
@@ -281,11 +281,21 @@ uint32_t dns_random(uint32_t upper_bound) {
 #endif
   case RNG_URANDOM: {
       uint32_t num = 0;
+      size_t attempts = 5;
       do {
-        if (read(urandom_fd, &num, sizeof(num)) < 0) {
+        ssize_t got = read(urandom_fd, &num, sizeof(num));
+        if (got < 0) {
           (void)close(urandom_fd);
           throw std::runtime_error("Cannot read random device");
         }
+        else if (static_cast<size_t>(got) != sizeof(num)) {
+          /* short read, let's retry */
+          if (attempts == 0) {
+            throw std::runtime_error("Too many short reads on random device");
+          }
+          attempts--;
+          continue;
+        }
       }
       while(num < min);
 
-- 
2.40.0