From 88795538726a5bbfd9efc13d441cb05e1d7fc139 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Tue, 27 Jun 2017 14:20:00 -0400 Subject: [PATCH] resolved: do not allocate packets with minimum size dns_packet_new() is sometimes called with mtu == 0, and in that case we should allocate more than the absolute minimum (which is the dns packet header size), otherwise we have to resize immediately again after appending the first data to the packet. This partially reverts the previous commit. --- src/resolve/resolved-dns-packet.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c index 821b66e..d1f0f76 100644 --- a/src/resolve/resolved-dns-packet.c +++ b/src/resolve/resolved-dns-packet.c @@ -28,6 +28,9 @@ #define EDNS0_OPT_DO (1<<15) +#define DNS_PACKET_SIZE_START 512 +assert_cc(DNS_PACKET_SIZE_START > UDP_PACKET_HEADER_SIZE) + typedef struct DnsPacketRewinder { DnsPacket *packet; size_t saved_rindex; @@ -47,7 +50,14 @@ int dns_packet_new(DnsPacket **ret, DnsProtocol protocol, size_t mtu) { assert(ret); - a = MAX(mtu, DNS_PACKET_HEADER_SIZE); + /* When dns_packet_new() is called with mtu == 0, allocate more than the + * absolute minimum (which is the dns packet header size), to avoid + * resizing immediately again after appending the first data to the packet. + */ + if (mtu < UDP_PACKET_HEADER_SIZE) + a = DNS_PACKET_SIZE_START; + else + a = MAX(mtu, DNS_PACKET_HEADER_SIZE); /* round up to next page size */ a = PAGE_ALIGN(ALIGN(sizeof(DnsPacket)) + a) - ALIGN(sizeof(DnsPacket)); -- 2.7.4