From ebca9ed2b2e62ee579100142ee61f5ba77a3c712 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Tue, 21 Jul 2026 13:28:23 +0100 Subject: [PATCH] [dns] Pass a non-null peer socket address to xfer_open_socket() Commit 3662065 ("[dns] Use all configured DNS servers") changed the logic from opening a single defined nameserver address to opening an unspecified peer socket address and then specifying the full peer address for each transmitted packet. The peer socket address was left unspecified by passing a null pointer to xfer_open_socket(). This is supported by the UDP socket opener, but technically violates the internal API (which allows the local socket address to be a null pointer, but not the peer socket address). In particular, in a debug build using DEBUG=open, the debug code will itself dereference the peer address pointer. Fix by embedding the name server socket address within the DNS request structure, and passing this to xfer_open_socket(). Signed-off-by: Michael Brown --- src/net/udp/dns.c | 33 +++++++++++++++++---------------- 1 file changed, 17 insertions(+), 16 deletions(-) diff --git a/src/net/udp/dns.c b/src/net/udp/dns.c index 3f534b99f..3f53675f9 100644 --- a/src/net/udp/dns.c +++ b/src/net/udp/dns.c @@ -466,6 +466,13 @@ struct dns_request { struct sockaddr_in sin; struct sockaddr_in6 sin6; } address; + /** Current name server address */ + union { + struct sockaddr sa; + struct sockaddr_tcpip st; + struct sockaddr_in sin; + struct sockaddr_in6 sin6; + } nameserver; /** Initial query type */ uint16_t qtype; /** Buffer for current query */ @@ -587,12 +594,6 @@ static int dns_question ( struct dns_request *dns ) { */ static int dns_send_packet ( struct dns_request *dns ) { struct dns_header *query = &dns->buf.query; - union { - struct sockaddr sa; - struct sockaddr_tcpip st; - struct sockaddr_in sin; - struct sockaddr_in6 sin6; - } nameserver; struct xfer_metadata meta; unsigned int index; @@ -600,25 +601,25 @@ static int dns_send_packet ( struct dns_request *dns ) { start_timer ( &dns->timer ); /* Construct DNS server address */ - memset ( &nameserver, 0, sizeof ( nameserver ) ); - nameserver.st.st_port = htons ( DNS_PORT ); + memset ( &dns->nameserver, 0, sizeof ( dns->nameserver ) ); + dns->nameserver.st.st_port = htons ( DNS_PORT ); if ( ! dns_count ) { DBGC ( dns, "DNS %p lost DNS servers mid query\n", dns ); return -EINVAL; } index = ( dns->index % dns_count ); if ( index < dns6.count ) { - nameserver.sin6.sin6_family = AF_INET6; - memcpy ( &nameserver.sin6.sin6_addr, &dns6.in6[index], - sizeof ( nameserver.sin6.sin6_addr ) ); + dns->nameserver.sin6.sin6_family = AF_INET6; + memcpy ( &dns->nameserver.sin6.sin6_addr, &dns6.in6[index], + sizeof ( dns->nameserver.sin6.sin6_addr ) ); } else { - nameserver.sin.sin_family = AF_INET; - nameserver.sin.sin_addr = dns4.in[index - dns6.count]; + dns->nameserver.sin.sin_family = AF_INET; + dns->nameserver.sin.sin_addr = dns4.in[index - dns6.count]; } /* Construct metadata */ memset ( &meta, 0, sizeof ( meta ) ); - meta.dest = &nameserver.sa; + meta.dest = &dns->nameserver.sa; /* Generate query identifier if applicable */ if ( ! query->id ) @@ -626,7 +627,7 @@ static int dns_send_packet ( struct dns_request *dns ) { /* Send query */ DBGC ( dns, "DNS %p sending %s query ID %#04x for %s type %s\n", dns, - sock_ntoa ( &nameserver.sa ), ntohs ( query->id ), + sock_ntoa ( &dns->nameserver.sa ), ntohs ( query->id ), dns_name ( &dns->name ), dns_type ( dns->question->qtype ) ); /* Send the data */ @@ -1030,7 +1031,7 @@ static int dns_resolv ( struct interface *resolv, /* Open UDP connection */ if ( ( rc = xfer_open_socket ( &dns->socket, SOCK_DGRAM, - NULL, NULL ) ) != 0 ) { + &dns->nameserver.sa, NULL ) ) != 0 ) { DBGC ( dns, "DNS %p could not open socket: %s\n", dns, strerror ( rc ) ); goto err_open_socket; -- 2.47.3