From: Tom Gundersen <teg@jklm.no>
Date: Wed, 24 Jun 2015 19:22:46 +0000 (+0200)
Subject: resolved: packet - ensure there is space for IP+UDP headers
X-Git-Tag: v223~105^2~4
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a0166609f782da91710dea9183d1bf138538db37;p=thirdparty%2Fsystemd.git

resolved: packet - ensure there is space for IP+UDP headers

Currently we only make sure our links can handle the size of the payload witohut
taking the headers into account.
---

diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
index fa0516f8a0c..a9cc5ca6aa5 100644
--- a/src/resolve/resolved-dns-packet.c
+++ b/src/resolve/resolved-dns-packet.c
@@ -32,10 +32,10 @@ int dns_packet_new(DnsPacket **ret, DnsProtocol protocol, size_t mtu) {
 
         assert(ret);
 
-        if (mtu <= 0)
+        if (mtu <= UDP_PACKET_HEADER_SIZE)
                 a = DNS_PACKET_SIZE_START;
         else
-                a = mtu;
+                a = mtu - UDP_PACKET_HEADER_SIZE;
 
         if (a < DNS_PACKET_HEADER_SIZE)
                 a = DNS_PACKET_HEADER_SIZE;
diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h
index bf998aa84ea..6588ed9df52 100644
--- a/src/resolve/resolved-dns-packet.h
+++ b/src/resolve/resolved-dns-packet.h
@@ -21,6 +21,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  ***/
 
+#include <netinet/udp.h>
+#include <netinet/ip.h>
 
 #include "macro.h"
 #include "sparse-endian.h"
@@ -53,6 +55,7 @@ struct DnsPacketHeader {
 };
 
 #define DNS_PACKET_HEADER_SIZE sizeof(DnsPacketHeader)
+#define UDP_PACKET_HEADER_SIZE (sizeof(struct iphdr) + sizeof(struct udphdr))
 
 /* The various DNS protocols deviate in how large a packet can grow,
    but the TCP transport has a 16bit size field, hence that appears to
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index 25392d21d71..e01e97be354 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -160,7 +160,7 @@ int dns_scope_emit(DnsScope *s, DnsPacket *p) {
                 if (p->size > DNS_PACKET_UNICAST_SIZE_MAX)
                         return -EMSGSIZE;
 
-                if (p->size > mtu)
+                if (p->size + UDP_PACKET_HEADER_SIZE > mtu)
                         return -EMSGSIZE;
 
                 if (family == AF_INET)