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

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Currently we only make sure our links can handle the size of the payload witohut
taking the headers into account.
This commit is contained in:
Tom Gundersen 2015-06-24 21:22:46 +02:00
parent ff89f8b917
commit a0166609f7
3 changed files with 6 additions and 3 deletions
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4
src/resolve/resolved-dns-packet.c
View file

@ -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;

3
src/resolve/resolved-dns-packet.h
View file

@ -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

2
src/resolve/resolved-dns-scope.c
View file

@ -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)