From 13e15dae9f0b4566d3ea2ed058a5dd44751216da Mon Sep 17 00:00:00 2001 From: Ronan Pigott Date: Mon, 26 Aug 2024 01:39:20 -0700 Subject: [PATCH] resolved: clear the AD bit for bypass packets When the bypass logic is invoked, such as for queries to the stub with the DO bit set, be certain to clear the AD bit in the reply before forwarding it if the answer is not known to be authentic. --- src/resolve/resolved-dns-packet.h | 1 + src/resolve/resolved-dns-stub.c | 10 ++++++++-- 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h index a2e25231df8..13d65a02c32 100644 --- a/src/resolve/resolved-dns-packet.h +++ b/src/resolve/resolved-dns-packet.h @@ -111,6 +111,7 @@ static inline uint8_t* DNS_PACKET_DATA(const DnsPacket *p) { #define DNS_PACKET_AD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 5) & 1) #define DNS_PACKET_CD(p) ((be16toh(DNS_PACKET_HEADER(p)->flags) >> 4) & 1) +#define DNS_PACKET_FLAG_AD (UINT16_C(1) << 5) #define DNS_PACKET_FLAG_TC (UINT16_C(1) << 9) static inline uint16_t DNS_PACKET_RCODE(DnsPacket *p) { diff --git a/src/resolve/resolved-dns-stub.c b/src/resolve/resolved-dns-stub.c index 23d4db9cd54..c604a51c4bb 100644 --- a/src/resolve/resolved-dns-stub.c +++ b/src/resolve/resolved-dns-stub.c @@ -685,7 +685,8 @@ static int dns_stub_send_failure( static int dns_stub_patch_bypass_reply_packet( DnsPacket **ret, /* Where to place the patched packet */ DnsPacket *original, /* The packet to patch */ - DnsPacket *request) { /* The packet the patched packet shall look like a reply to */ + DnsPacket *request, /* The packet the patched packet shall look like a reply to */ + bool authenticated) { _cleanup_(dns_packet_unrefp) DnsPacket *c = NULL; int r; @@ -725,6 +726,10 @@ static int dns_stub_patch_bypass_reply_packet( DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) | DNS_PACKET_FLAG_TC); } + /* Ensure we don't pass along an untrusted ad flag for bypass packets */ + if (!authenticated) + DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) & ~DNS_PACKET_FLAG_AD); + *ret = TAKE_PTR(c); return 0; } @@ -745,7 +750,8 @@ static void dns_stub_query_complete(DnsQuery *query) { q->answer_full_packet->protocol == DNS_PROTOCOL_DNS) { _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; - r = dns_stub_patch_bypass_reply_packet(&reply, q->answer_full_packet, q->request_packet); + r = dns_stub_patch_bypass_reply_packet(&reply, q->answer_full_packet, q->request_packet, + FLAGS_SET(q->answer_query_flags, SD_RESOLVED_AUTHENTICATED)); if (r < 0) log_debug_errno(r, "Failed to patch bypass reply packet: %m"); else