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-rw-r--r--src/resolve/resolved-dns-packet.c4
-rw-r--r--src/resolve/resolved-dns-packet.h3
-rw-r--r--src/resolve/resolved-dns-scope.c2
3 files changed, 6 insertions, 3 deletions
diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
index fa0516f8a0..a9cc5ca6aa 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 bf998aa84e..6588ed9df5 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 25392d21d7..e01e97be35 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)