458 lines
15 KiB
Diff
458 lines
15 KiB
Diff
From f568270c4ec5b0472e0a49af510fd58f1f65155b Mon Sep 17 00:00:00 2001
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From: Mara Sophie Grosch <littlefox@lf-net.org>
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Date: Sat, 13 Feb 2021 23:01:02 +0100
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Subject: [PATCH 1/3] Resolve SRV record for hostname
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Very crude first implementation, needs more polishing.
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Only tries to resolve via SRV if a port is not given manually, via
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config or command line.
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Only the highest-prio lowest-weight host is used currently, it does
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not do load balancing! Still useful for non-standard ports.
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Working towards fixing https://bugzilla.mindrot.org/show_bug.cgi?id=2217
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---
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dns.c | 2 +-
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dns.h | 3 ++
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ssh.c | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
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3 files changed, 135 insertions(+), 14 deletions(-)
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diff --git a/dns.c b/dns.c
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index 939241440..e4423655e 100644
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--- a/dns.c
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+++ b/dns.c
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@@ -52,7 +52,7 @@ static const char * const errset_text[] = {
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"data does not exist", /* 5 ERRSET_NODATA */
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};
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-static const char *
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+const char *
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dns_result_totext(unsigned int res)
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{
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switch (res) {
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diff --git a/dns.h b/dns.h
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index 864ab7d00..bba0095db 100644
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--- a/dns.h
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+++ b/dns.h
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@@ -46,6 +46,7 @@ enum sshfp_hashes {
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#define DNS_RDATACLASS_IN 1
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#define DNS_RDATATYPE_SSHFP 44
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+#define DNS_RDATATYPE_SRV 33
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#define DNS_VERIFY_FOUND 0x00000001
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#define DNS_VERIFY_MATCH 0x00000002
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@@ -56,4 +57,6 @@ int verify_host_key_dns(const char *, struct sockaddr *,
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struct sshkey *, int *);
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int export_dns_rr(const char *, struct sshkey *, FILE *, int, int);
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+const char* dns_result_totext(unsigned int res);
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+
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#endif /* DNS_H */
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diff --git a/ssh.c b/ssh.c
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index 0019281f4..95871013f 100644
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--- a/ssh.c
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+++ b/ssh.c
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@@ -108,6 +108,7 @@
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#include "ssherr.h"
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#include "myproposal.h"
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#include "utf8.h"
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+#include "dns.h"
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#ifdef ENABLE_PKCS11
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#include "ssh-pkcs11.h"
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@@ -243,6 +244,105 @@ default_client_percent_dollar_expand(const char *str,
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return ret;
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}
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+/*
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+ * Attempt to resolve _ssh._tcp.$orig_name SRV record to the highest-priority
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+ * host and port.
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+ * Returns the port of the target service via out-argument
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+ * Returns NULL on failure and when no SRV record is found.
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+ */
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+static char *
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+resolve_srv(const char* orig_name, int *port) {
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+ const size_t prefix_len = 10;
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+ const size_t orig_len = strlen(orig_name);
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+ char* name = malloc(prefix_len + orig_len + 1);
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+ snprintf(name, prefix_len + orig_len + 1, "_ssh._tcp.%s", orig_name);
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+
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+ debug3_f("Trying to lookup SRV for: %s (%s)", orig_name, name);
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+
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+ struct rrsetinfo *srvs = NULL;
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+ int result = getrrsetbyname(name, DNS_RDATACLASS_IN, DNS_RDATATYPE_SRV, 0, &srvs);
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+
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+ if(result) {
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+ debug2_f("SRV lookup error: %s", dns_result_totext(result));
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+ goto fail;
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+ }
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+
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+ if(!srvs->rri_nrdatas) {
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+ debug2_f("No SRV records found for %s", name);
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+ goto fail;
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+ }
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+
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+ uint16_t cur_prio = UINT16_MAX;
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+ uint16_t cur_weight = 0;
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+ uint16_t cur_port = 0;
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+ char* cur_target = NULL;
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+
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+ for(unsigned i = 0; i < srvs->rri_nrdatas; ++i) {
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+ struct rdatainfo srv = srvs->rri_rdatas[i];
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+
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+ if(srv.rdi_length >= 9) {
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+ uint16_t prio = ntohs(*(uint16_t*)srv.rdi_data);
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+ uint16_t weight = ntohs(*(uint16_t*)(srv.rdi_data + 2));
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+ uint16_t port = ntohs(*(uint16_t*)(srv.rdi_data + 4));
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+
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+ if(prio < cur_prio || (prio == cur_prio && weight > cur_weight)) {
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+ const char* target_labels = srv.rdi_data + 6;
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+ size_t target_index = 0;
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+
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+ char* target = NULL;
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+ size_t target_size = 0;
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+
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+ uint8_t next_label_len;
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+ do {
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+ next_label_len = target_labels[target_index];
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+
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+ char* old_target = target;
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+
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+ if(old_target) {
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+ target = malloc(target_size + next_label_len + 2);
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+ memcpy(target, old_target, target_size);
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+ target[target_size] = '.';
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+ memcpy(target + target_size + 1, target_labels + target_index + 1, next_label_len);
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+ target[target_size + next_label_len + 1] = 0;
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+
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+ target_size += 1;
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+
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+ free(old_target);
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+ }
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+ else {
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+ target = malloc(next_label_len + 1);
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+ memcpy(target, target_labels + target_index + 1, next_label_len);
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+ target[next_label_len] = 0;
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+ }
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+
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+ target_size += next_label_len;
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+ target_index += next_label_len + 1;
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+ } while(next_label_len > 0 && target_index + next_label_len <= srv.rdi_length - 6);
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+
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+ debug2_f("Found SRV record pointing at %s:%u (weight %u, prio %u)", target, port, weight, prio);
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+
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+ cur_port = port;
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+ cur_target = target;
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+ cur_weight = weight;
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+ cur_prio = prio;
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+ }
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+ }
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+ }
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+
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+fail:
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+ freerrset(srvs);
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+ free(name);
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+
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+ if(cur_target) {
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+ debug_f("Connecting via SRV record to %s:%u", cur_target, cur_port);
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+
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+ *port = cur_port;
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+ return cur_target;
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+ }
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+
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+ return NULL;
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+}
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+
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/*
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* Attempt to resolve a host name / port to a set of addresses and
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* optionally return any CNAMEs encountered along the way.
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@@ -250,21 +350,34 @@ default_client_percent_dollar_expand(const char *str,
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* NB. this function must operate with a options having undefined members.
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*/
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static struct addrinfo *
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-resolve_host(const char *name, int port, int logerr, char *cname, size_t clen)
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+resolve_host(const char *orig_name, int *port, int logerr, char *cname, size_t clen)
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{
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+ char* name = NULL;
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+
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+ if(*port <= 0) {
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+ name = resolve_srv(orig_name, port);
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+ }
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+
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+ if(!name) {
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+ name = malloc(strlen(orig_name) + 1);
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+ strcpy(name, orig_name);
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+ }
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+
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char strport[NI_MAXSERV];
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const char *errstr = NULL;
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struct addrinfo hints, *res;
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int gaierr;
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LogLevel loglevel = SYSLOG_LEVEL_DEBUG1;
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- if (port <= 0)
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- port = default_ssh_port();
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- if (cname != NULL)
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+ if (*port <= 0) {
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+ *port = default_ssh_port();
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+ }
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+ if (cname != NULL) {
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*cname = '\0';
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- debug3_f("lookup %s:%d", name, port);
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+ }
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+ debug3_f("lookup %s:%d", name, *port);
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- snprintf(strport, sizeof strport, "%d", port);
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+ snprintf(strport, sizeof strport, "%d", *port);
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memset(&hints, 0, sizeof(hints));
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hints.ai_family = options.address_family == -1 ?
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AF_UNSPEC : options.address_family;
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@@ -276,6 +389,7 @@ resolve_host(const char *name, int port, int logerr, char *cname, size_t clen)
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loglevel = SYSLOG_LEVEL_ERROR;
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do_log2(loglevel, "%s: Could not resolve hostname %.100s: %s",
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__progname, name, ssh_gai_strerror(gaierr));
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+ free(name);
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return NULL;
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}
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if (cname != NULL && res->ai_canonname != NULL) {
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@@ -289,6 +403,8 @@ resolve_host(const char *name, int port, int logerr, char *cname, size_t clen)
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*cname = '\0';
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}
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}
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+
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+ free(name);
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return res;
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}
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@@ -423,7 +539,7 @@ check_follow_cname(int direct, char **namep, const char *cname)
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* NB. this function must operate with a options having undefined members.
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*/
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static struct addrinfo *
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-resolve_canonicalize(char **hostp, int port)
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+resolve_canonicalize(char **hostp, int *port)
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{
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int i, direct, ndots;
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char *cp, *fullhost, newname[NI_MAXHOST];
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@@ -433,7 +549,7 @@ resolve_canonicalize(char **hostp, int port)
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* Attempt to canonicalise addresses, regardless of
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* whether hostname canonicalisation was requested
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*/
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- if ((addrs = resolve_addr(*hostp, port,
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+ if ((addrs = resolve_addr(*hostp, *port,
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newname, sizeof(newname))) != NULL) {
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debug2_f("hostname %.100s is address", *hostp);
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if (strcasecmp(*hostp, newname) != 0) {
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@@ -1227,12 +1343,14 @@ main(int ac, char **av)
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if ((was_addr = is_addr(host)) == 0)
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lowercase(host);
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+ int port = options.port;
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+
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/*
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* Try to canonicalize if requested by configuration or the
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* hostname is an address.
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*/
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if (options.canonicalize_hostname != SSH_CANONICALISE_NO || was_addr)
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- addrs = resolve_canonicalize(&host, options.port);
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+ addrs = resolve_canonicalize(&host, &port);
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/*
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* If CanonicalizePermittedCNAMEs have been specified but
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@@ -1251,7 +1369,7 @@ main(int ac, char **av)
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option_clear_or_none(options.jump_host);
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if (addrs == NULL && config_has_permitted_cnames(&options) && (direct ||
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options.canonicalize_hostname == SSH_CANONICALISE_ALWAYS)) {
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- if ((addrs = resolve_host(host, options.port,
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+ if ((addrs = resolve_host(host, &port,
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direct, cname, sizeof(cname))) == NULL) {
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/* Don't fatal proxied host names not in the DNS */
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if (direct)
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@@ -1280,8 +1398,8 @@ main(int ac, char **av)
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* enabled and the port number may have changed since, so
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* reset it in address list
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*/
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- if (addrs != NULL && options.port > 0)
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- set_addrinfo_port(addrs, options.port);
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+ if (addrs != NULL && port > 0)
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+ set_addrinfo_port(addrs, port);
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}
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/* Fill configuration defaults. */
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@@ -1606,7 +1724,7 @@ main(int ac, char **av)
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*/
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if (addrs == NULL && options.proxy_command == NULL) {
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debug2("resolving \"%s\" port %d", host, options.port);
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- if ((addrs = resolve_host(host, options.port, 1,
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+ if ((addrs = resolve_host(host, &port, 1,
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cname, sizeof(cname))) == NULL)
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cleanup_exit(255); /* resolve_host logs the error */
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}
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--
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2.44.1
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From 885aca548189e24d50431f59b1c7c14b378c4d91 Mon Sep 17 00:00:00 2001
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From: Mara Sophie Grosch <littlefox@lf-net.org>
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Date: Sat, 13 Feb 2021 23:12:31 +0100
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Subject: [PATCH 2/3] Move DNS name decoding to dns.{c/h}
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---
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dns.c | 43 +++++++++++++++++++++++++++++++++++++++++++
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dns.h | 2 ++
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ssh.c | 38 +++-----------------------------------
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3 files changed, 48 insertions(+), 35 deletions(-)
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diff --git a/dns.c b/dns.c
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index e4423655e..ab156f5c3 100644
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--- a/dns.c
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+++ b/dns.c
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@@ -342,3 +342,46 @@ export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic,
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return success;
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}
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+
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+/*
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+ * Decoded a DNS wire-format name to the commonly
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+ * used, dot-separated format of labels.
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+ * Returns a dynamically allocated string on success
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+ * and NULL on error.
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+ */
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+char*
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+dns_decode_name(const char* data, size_t len) {
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+ size_t index = 0;
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+
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+ char* decoded = NULL;
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+ size_t size = 0;
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+
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+ uint8_t next_label_len;
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+ do {
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+ next_label_len = data[index];
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+
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+ char* old_decoded = decoded;
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+
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+ if(old_decoded) {
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+ decoded = malloc(size + next_label_len + 2);
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+ memcpy(decoded, old_decoded, size);
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+ decoded[size] = '.';
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+ memcpy(decoded + size + 1, data + index + 1, next_label_len);
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+ decoded[size + next_label_len + 1] = 0;
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+
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+ size += 1;
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+
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+ free(old_decoded);
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+ }
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+ else {
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+ decoded = malloc(next_label_len + 1);
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+ memcpy(decoded, data + index + 1, next_label_len);
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+ decoded[next_label_len] = 0;
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+ }
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+
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+ size += next_label_len;
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+ index += next_label_len + 1;
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+ } while(next_label_len > 0 && index + next_label_len <= len);
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+
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+ return decoded;
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+}
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diff --git a/dns.h b/dns.h
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index bba0095db..e0a737f12 100644
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--- a/dns.h
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+++ b/dns.h
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@@ -59,4 +59,6 @@ int export_dns_rr(const char *, struct sshkey *, FILE *, int, int);
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const char* dns_result_totext(unsigned int res);
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+char* dns_decode_name(const char* data, size_t len);
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+
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#endif /* DNS_H */
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diff --git a/ssh.c b/ssh.c
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index 95871013f..c295653e4 100644
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--- a/ssh.c
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+++ b/ssh.c
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@@ -284,43 +284,11 @@ resolve_srv(const char* orig_name, int *port) {
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uint16_t prio = ntohs(*(uint16_t*)srv.rdi_data);
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uint16_t weight = ntohs(*(uint16_t*)(srv.rdi_data + 2));
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uint16_t port = ntohs(*(uint16_t*)(srv.rdi_data + 4));
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+ char* target = dns_decode_name(srv.rdi_data + 6, srv.rdi_length - 6);
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- if(prio < cur_prio || (prio == cur_prio && weight > cur_weight)) {
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- const char* target_labels = srv.rdi_data + 6;
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- size_t target_index = 0;
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-
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- char* target = NULL;
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- size_t target_size = 0;
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-
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- uint8_t next_label_len;
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- do {
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- next_label_len = target_labels[target_index];
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-
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- char* old_target = target;
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-
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- if(old_target) {
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- target = malloc(target_size + next_label_len + 2);
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- memcpy(target, old_target, target_size);
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- target[target_size] = '.';
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- memcpy(target + target_size + 1, target_labels + target_index + 1, next_label_len);
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- target[target_size + next_label_len + 1] = 0;
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-
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- target_size += 1;
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-
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- free(old_target);
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- }
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- else {
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- target = malloc(next_label_len + 1);
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- memcpy(target, target_labels + target_index + 1, next_label_len);
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- target[next_label_len] = 0;
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- }
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-
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- target_size += next_label_len;
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- target_index += next_label_len + 1;
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- } while(next_label_len > 0 && target_index + next_label_len <= srv.rdi_length - 6);
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-
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- debug2_f("Found SRV record pointing at %s:%u (weight %u, prio %u)", target, port, weight, prio);
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+ debug2_f("Found SRV record pointing at %s:%u (weight %u, prio %u)", target, port, weight, prio);
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+ if(prio < cur_prio || (prio == cur_prio && weight > cur_weight)) {
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cur_port = port;
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cur_target = target;
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cur_weight = weight;
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--
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2.44.1
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From afa1e00156dc0fb899e3ed48d08480cece390d03 Mon Sep 17 00:00:00 2001
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From: Mara Sophie Grosch <littlefox@lf-net.org>
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Date: Sun, 14 Feb 2021 00:35:53 +0100
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Subject: [PATCH 3/3] Code reordering: fix uninitialized use
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---
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ssh.c | 5 +++--
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1 file changed, 3 insertions(+), 2 deletions(-)
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diff --git a/ssh.c b/ssh.c
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index c295653e4..144825214 100644
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--- a/ssh.c
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+++ b/ssh.c
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@@ -252,6 +252,9 @@ default_client_percent_dollar_expand(const char *str,
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*/
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static char *
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resolve_srv(const char* orig_name, int *port) {
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+ uint16_t cur_port = 0;
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+ char* cur_target = NULL;
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+
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const size_t prefix_len = 10;
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const size_t orig_len = strlen(orig_name);
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char* name = malloc(prefix_len + orig_len + 1);
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@@ -274,8 +277,6 @@ resolve_srv(const char* orig_name, int *port) {
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uint16_t cur_prio = UINT16_MAX;
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uint16_t cur_weight = 0;
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- uint16_t cur_port = 0;
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- char* cur_target = NULL;
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for(unsigned i = 0; i < srvs->rri_nrdatas; ++i) {
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struct rdatainfo srv = srvs->rri_rdatas[i];
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--
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2.44.1
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