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universe/overlays/patches/srv-records.patch

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