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socks: use dns filter for resolving

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Use a dns connection filter to resolve hostnames where their addresses
are locally resolved and forwarded to the SOCKS proxy.

This makes all improvements, like in #21295 for example, also apply
to socks connections. Curl_resolv() is now only called from a DNS
filter.

(ftp still calls Curl_resolv_blocking() in two places, one of which
 may be replaceable with a DNS filter as well to remove the block, tbd)

Closes #21297
This commit is contained in:
Stefan Eissing 2026-04-13 12:57:11 +02:00 • committed by Daniel Stenberg
parent 0567e72168
commit bcd94e2750
No known key found for this signature in database
GPG key ID: 5CC908FDB71E12C2
3 changed files with 74 additions and 92 deletions
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122
lib/socks.c
View file

@ -38,6 +38,7 @@
#include "curl_trc.h"
#include "select.h"
#include "cfilters.h"
#include "cf-dns.h"
#include "connect.h"
#include "socks.h"
#include "curlx/inet_pton.h"
@ -313,71 +314,54 @@ static CURLproxycode socks4_resolving(struct socks_state *sx,
struct Curl_easy *data,
bool *done)
{
struct Curl_dns_entry *dns = NULL;
struct Curl_addrinfo *hp = NULL;
const struct Curl_addrinfo *ai = NULL;
CURLcode result;
size_t nwritten;
bool dns_done;
*done = FALSE;
if(sx->start_resolving) {
/* need to resolve hostname to add destination address */
sx->start_resolving = FALSE;
DEBUGASSERT(sx->hostname && *sx->hostname);
result = Curl_resolv(data,
Curl_resolv_dns_queries(data, cf->conn->ip_version),
sx->hostname, sx->remote_port,
Curl_conn_cf_get_transport(cf, data),
0, &sx->resolv_id, &dns);
if(result == CURLE_AGAIN) {
CURL_TRC_CF(data, cf, "SOCKS4 non-blocking resolve of %s", sx->hostname);
return CURLPX_OK;
result = Curl_cf_dns_insert_after(
cf, data, Curl_resolv_dns_queries(data, cf->conn->ip_version),
sx->hostname, sx->remote_port, TRNSPRT_TCP, TRUE);
if(result) {
failf(data, "unable to create DNS filter for socks");
return CURLPX_UNKNOWN_FAIL;
}
else if(result)
return CURLPX_RESOLVE_HOST;
}
else {
/* check if we have the name resolved by now */
result = Curl_resolv_take_result(data, sx->resolv_id, &dns);
if(!result && !dns)
return CURLPX_OK;
}
if(result || !dns) {
failf(data, "Failed to resolve \"%s\" for SOCKS4 connect.", sx->hostname);
if(dns)
Curl_dns_entry_unlink(data, &dns);
/* resolve the hostname by connecting the DNS filter */
result = Curl_conn_cf_connect(cf->next, data, &dns_done);
if(result) {
failf(data, "Failed to resolve \"%s\" for SOCKS4 connect.",
sx->hostname);
return CURLPX_RESOLVE_HOST;
}
else if(!dns_done)
return CURLPX_OK;
/*
* We cannot use 'hostent' as a struct that Curl_resolv() returns. It
* returns a Curl_addrinfo pointer that may not always look the same.
*/
/* scan for the first IPv4 address */
hp = dns->addr;
while(hp && (hp->ai_family != AF_INET))
hp = hp->ai_next;
if(hp) {
ai = Curl_cf_dns_get_ai(cf->next, data, AF_INET, 0);
if(ai) {
struct sockaddr_in *saddr_in;
char ipbuf[64];
Curl_printable_address(hp, ipbuf, sizeof(ipbuf));
Curl_printable_address(ai, ipbuf, sizeof(ipbuf));
CURL_TRC_CF(data, cf, "SOCKS4 connect to IPv4 %s (locally resolved)",
ipbuf);
saddr_in = (struct sockaddr_in *)(void *)hp->ai_addr;
saddr_in = (struct sockaddr_in *)(void *)ai->ai_addr;
result = Curl_bufq_write(&sx->iobuf,
(unsigned char *)&saddr_in->sin_addr.s_addr, 4,
&nwritten);
Curl_dns_entry_unlink(data, &dns); /* not used anymore from now on */
if(result || (nwritten != 4))
return CURLPX_SEND_REQUEST;
}
else {
Curl_dns_entry_unlink(data, &dns);
/* No ipv4 address resolved */
failf(data, "SOCKS4 connection to %s not supported", sx->hostname);
return CURLPX_RESOLVE_HOST;
}
@ -844,8 +828,7 @@ static CURLproxycode socks5_resolving(struct socks_state *sx,
struct Curl_easy *data,
bool *done)
{
struct Curl_dns_entry *dns = NULL;
struct Curl_addrinfo *hp = NULL;
const struct Curl_addrinfo *ai = NULL;
char dest[MAX_IPADR_LEN]; /* printable address */
const unsigned char *destination = NULL;
unsigned char desttype = 1, destlen = 4;
@ -853,72 +836,61 @@ static CURLproxycode socks5_resolving(struct socks_state *sx,
CURLcode result;
CURLproxycode presult = CURLPX_OK;
size_t nwritten;
bool dns_done;
*done = FALSE;
if(sx->start_resolving) {
/* need to resolve hostname to add destination address */
sx->start_resolving = FALSE;
DEBUGASSERT(sx->hostname && *sx->hostname);
result = Curl_resolv(data,
Curl_resolv_dns_queries(data, cf->conn->ip_version),
sx->hostname, sx->remote_port,
Curl_conn_cf_get_transport(cf, data),
0, &sx->resolv_id, &dns);
if(result == CURLE_AGAIN) {
CURL_TRC_CF(data, cf, "SOCKS5 non-blocking resolve of %s", sx->hostname);
return CURLPX_OK;
result = Curl_cf_dns_insert_after(
cf, data, Curl_resolv_dns_queries(data, cf->conn->ip_version),
sx->hostname, sx->remote_port, TRNSPRT_TCP, TRUE);
if(result) {
failf(data, "unable to create DNS filter for socks");
return CURLPX_UNKNOWN_FAIL;
}
else if(result)
return CURLPX_RESOLVE_HOST;
}
else {
/* check if we have the name resolved by now */
result = Curl_resolv_take_result(data, sx->resolv_id, &dns);
if(!result && !dns)
return CURLPX_OK;
}
if(result || !dns) {
/* resolve the hostname by connecting the DNS filter */
result = Curl_conn_cf_connect(cf->next, data, &dns_done);
if(result) {
failf(data, "Failed to resolve \"%s\" for SOCKS5 connect.", sx->hostname);
presult = CURLPX_RESOLVE_HOST;
goto out;
return CURLPX_RESOLVE_HOST;
}
else if(!dns_done)
return CURLPX_OK;
if(dns)
hp = dns->addr;
#ifdef USE_IPV6
if(data->set.ipver != CURL_IPRESOLVE_WHATEVER) {
int wanted_family = data->set.ipver == CURL_IPRESOLVE_V4 ?
AF_INET : AF_INET6;
/* scan for the first proper address */
while(hp && (hp->ai_family != wanted_family))
hp = hp->ai_next;
}
if(data->set.ipver != CURL_IPRESOLVE_V4)
ai = Curl_cf_dns_get_ai(cf->next, data, AF_INET6, 0);
#endif
if(!hp) {
if(!ai)
ai = Curl_cf_dns_get_ai(cf->next, data, AF_INET, 0);
if(!ai) {
failf(data, "Failed to resolve \"%s\" for SOCKS5 connect.", sx->hostname);
presult = CURLPX_RESOLVE_HOST;
goto out;
}
Curl_printable_address(hp, dest, sizeof(dest));
Curl_printable_address(ai, dest, sizeof(dest));
if(hp->ai_family == AF_INET) {
if(ai->ai_family == AF_INET) {
struct sockaddr_in *saddr_in;
desttype = 1; /* ATYP: IPv4 = 1 */
destlen = 4;
saddr_in = (struct sockaddr_in *)(void *)hp->ai_addr;
saddr_in = (struct sockaddr_in *)(void *)ai->ai_addr;
destination = (const unsigned char *)&saddr_in->sin_addr.s_addr;
CURL_TRC_CF(data, cf, "SOCKS5 connect to %s:%u (locally resolved)",
dest, sx->remote_port);
}
#ifdef USE_IPV6
else if(hp->ai_family == AF_INET6) {
else if(ai->ai_family == AF_INET6) {
struct sockaddr_in6 *saddr_in6;
desttype = 4; /* ATYP: IPv6 = 4 */
destlen = 16;
saddr_in6 = (struct sockaddr_in6 *)(void *)hp->ai_addr;
saddr_in6 = (struct sockaddr_in6 *)(void *)ai->ai_addr;
destination = (const unsigned char *)&saddr_in6->sin6_addr.s6_addr;
CURL_TRC_CF(data, cf, "SOCKS5 connect to [%s]:%u (locally resolved)",
dest, sx->remote_port);
@ -952,8 +924,6 @@ static CURLproxycode socks5_resolving(struct socks_state *sx,
}
out:
if(dns)
Curl_dns_entry_unlink(data, &dns);
*done = (presult == CURLPX_OK);
return presult;
}