From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Mon, 27 Apr 2020 14:48:16 +0000 (+0200)
Subject: Don't read potentially uninitalized memory if gethostname() failed
X-Git-Tag: rec-4.3.1^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F9115%2Fhead;p=thirdparty%2Fpdns.git

Don't read potentially uninitalized memory if gethostname() failed

If the buffer is smaller than `HOST_NAME_MAX` (64 on Linux but up to
255 bytes in POSIX, which FreeBSD, MacOS etc honor) gethostname()
might return -1 without null-terminating the buffer, causing an
out-of-bounds read.
As we look for the first '.' using `strchr()`, replacing it with a
null byte, we also have a one-byte out-of-bounds write which might
result in a crash or, albeit very unlikely, arbitrary code execution.

(cherry picked from commit aac6348d56f6f3fdba9dd2455ef06081da507c14)
---

diff --git a/pdns/rec-carbon.cc b/pdns/rec-carbon.cc
index 218ee83716..4e0cedb00f 100644
--- a/pdns/rec-carbon.cc
+++ b/pdns/rec-carbon.cc
@@ -33,9 +33,11 @@ try
     namespace_name="pdns";
   }
   if(hostname.empty()) {
-    char tmp[80];
+    char tmp[HOST_NAME_MAX+1];
     memset(tmp, 0, sizeof(tmp));
-    gethostname(tmp, sizeof(tmp));
+    if (gethostname(tmp, sizeof(tmp)) != 0) {
+      throw std::runtime_error("The 'carbon-ourname' setting has not been set and we are unable to determine the system's hostname: " + stringerror());
+    }
     char *p = strchr(tmp, '.');
     if(p) *p=0;