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From b38575cb49041e586b0732d759a06801e587bb90 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Tue, 27 Jun 2017 14:20:00 -0400
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Subject: [PATCH] resolved: do not allocate packets with minimum size
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dns_packet_new() is sometimes called with mtu == 0, and in that case we should
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allocate more than the absolute minimum (which is the dns packet header size),
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otherwise we have to resize immediately again after appending the first data to
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the packet.
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This partially reverts the previous commit.
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(cherry picked from commit 88795538726a5bbfd9efc13d441cb05e1d7fc139)
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---
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src/resolve/resolved-dns-packet.c | 12 +++++++++++-
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1 file changed, 11 insertions(+), 1 deletion(-)
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diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
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index 821b66e266..d1f0f760a4 100644
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--- a/src/resolve/resolved-dns-packet.c
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+++ b/src/resolve/resolved-dns-packet.c
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@@ -28,6 +28,9 @@
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#define EDNS0_OPT_DO (1<<15)
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+#define DNS_PACKET_SIZE_START 512
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+assert_cc(DNS_PACKET_SIZE_START > UDP_PACKET_HEADER_SIZE)
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+
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typedef struct DnsPacketRewinder {
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DnsPacket *packet;
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size_t saved_rindex;
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@@ -47,7 +50,14 @@ int dns_packet_new(DnsPacket **ret, DnsProtocol protocol, size_t mtu) {
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assert(ret);
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- a = MAX(mtu, DNS_PACKET_HEADER_SIZE);
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+ /* When dns_packet_new() is called with mtu == 0, allocate more than the
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+ * absolute minimum (which is the dns packet header size), to avoid
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+ * resizing immediately again after appending the first data to the packet.
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+ */
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+ if (mtu < UDP_PACKET_HEADER_SIZE)
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+ a = DNS_PACKET_SIZE_START;
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+ else
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+ a = MAX(mtu, DNS_PACKET_HEADER_SIZE);
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/* round up to next page size */
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a = PAGE_ALIGN(ALIGN(sizeof(DnsPacket)) + a) - ALIGN(sizeof(DnsPacket));
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--
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2.13.0
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