[PATCH 1 of 2] The "ipv4=" parameter of the "resolver" directive
Sergey Kandaurov
pluknet at nginx.com
Wed Jul 13 15:03:31 UTC 2022
> On 28 Jun 2022, at 20:25, Sergey Kandaurov <pluknet at nginx.com> wrote:
>
> # HG changeset patch
> # User Ruslan Ermilov <ru at nginx.com>
> # Date 1645589317 -10800
> # Wed Feb 23 07:08:37 2022 +0300
> # Node ID 04e314eb6b4d20a48c5d7bab0609e1b03b51b406
> # Parent fecd73db563fb64108f7669eca419badb2aba633
> The "ipv4=" parameter of the "resolver" directive.
>
> When set to "off", only IPv6 addresses will be resolved, and no
> A queries are ever sent (ticket #2196).
>
> diff -r fecd73db563f -r 04e314eb6b4d src/core/ngx_resolver.c
> --- a/src/core/ngx_resolver.c Tue Jun 21 17:25:37 2022 +0300
> +++ b/src/core/ngx_resolver.c Wed Feb 23 07:08:37 2022 +0300
> @@ -157,6 +157,8 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
> cln->handler = ngx_resolver_cleanup;
> cln->data = r;
>
> + r->ipv4 = 1;
> +
> ngx_rbtree_init(&r->name_rbtree, &r->name_sentinel,
> ngx_resolver_rbtree_insert_value);
>
> @@ -225,6 +227,23 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
> }
>
> #if (NGX_HAVE_INET6)
> + if (ngx_strncmp(names[i].data, "ipv4=", 5) == 0) {
> +
> + if (ngx_strcmp(&names[i].data[5], "on") == 0) {
> + r->ipv4 = 1;
> +
> + } else if (ngx_strcmp(&names[i].data[5], "off") == 0) {
> + r->ipv4 = 0;
> +
> + } else {
> + ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
> + "invalid parameter: %V", &names[i]);
> + return NULL;
> + }
> +
> + continue;
> + }
> +
> if (ngx_strncmp(names[i].data, "ipv6=", 5) == 0) {
>
> if (ngx_strcmp(&names[i].data[5], "on") == 0) {
> @@ -273,6 +292,14 @@ ngx_resolver_create(ngx_conf_t *cf, ngx_
> }
> }
>
> +#if (NGX_HAVE_INET6)
> + if (r->ipv4 + r->ipv6 == 0) {
> + ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
> + "\"ipv4\" and \"ipv6\" cannot both be \"off\"");
> + return NULL;
> + }
> +#endif
> +
> if (n && r->connections.nelts == 0) {
> ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "no name servers defined");
> return NULL;
> @@ -836,7 +863,7 @@ ngx_resolve_name_locked(ngx_resolver_t *
> r->last_connection = 0;
> }
>
> - rn->naddrs = (u_short) -1;
> + rn->naddrs = r->ipv4 ? (u_short) -1 : 0;
> rn->tcp = 0;
> #if (NGX_HAVE_INET6)
> rn->naddrs6 = r->ipv6 ? (u_short) -1 : 0;
> @@ -1263,7 +1290,7 @@ ngx_resolver_send_query(ngx_resolver_t *
> rec->log.action = "resolving";
> }
>
> - if (rn->naddrs == (u_short) -1) {
> + if (rn->query && rn->naddrs == (u_short) -1) {
It should be safe to revert this condition:
for PTR and SRV queries, rn->query is always set;
for A queries, it is additionally protected with rn->naddrs,
which by itself is set to (u_short) -1 only for r->ipv4 == 1.
See below for rationale.
> rc = rn->tcp ? ngx_resolver_send_tcp_query(r, rec, rn->query, rn->qlen)
> : ngx_resolver_send_udp_query(r, rec, rn->query, rn->qlen);
>
> @@ -1765,10 +1792,13 @@ ngx_resolver_process_response(ngx_resolv
> q = ngx_queue_next(q))
> {
> rn = ngx_queue_data(q, ngx_resolver_node_t, queue);
> - qident = (rn->query[0] << 8) + rn->query[1];
> -
> - if (qident == ident) {
> - goto dns_error_name;
> +
> + if (rn->query) {
> + qident = (rn->query[0] << 8) + rn->query[1];
> +
> + if (qident == ident) {
> + goto dns_error_name;
> + }
This one also looks save to revert.
This code is used to check ident match for the FORMERR case.
For ipv4=off case, with the below part reverted, both rn->query
and rn->query6 will look at the same address, so on ident mismatch
both checks for rn->query and rn->query6 just duplicate each other.
> }
>
> #if (NGX_HAVE_INET6)
> @@ -3645,7 +3675,7 @@ ngx_resolver_create_name_query(ngx_resol
> len = sizeof(ngx_resolver_hdr_t) + nlen + sizeof(ngx_resolver_qs_t);
>
> #if (NGX_HAVE_INET6)
> - p = ngx_resolver_alloc(r, r->ipv6 ? len * 2 : len);
> + p = ngx_resolver_alloc(r, len * (r->ipv4 + r->ipv6));
> #else
> p = ngx_resolver_alloc(r, len);
> #endif
> @@ -3654,23 +3684,28 @@ ngx_resolver_create_name_query(ngx_resol
> }
>
> rn->qlen = (u_short) len;
> - rn->query = p;
> +
> + if (r->ipv4) {
> + rn->query = p;
> + }
It turns out that doing conditional allocation prevents from
memory deallocation using "ngx_resolver_free(r, rn->query);" idiom.
Reverting this part and accompanying changes for rn->query
seems to be enough to fix this.
See above for more details, and the patch below.
>
> #if (NGX_HAVE_INET6)
> if (r->ipv6) {
> - rn->query6 = p + len;
> + rn->query6 = r->ipv4 ? (p + len) : p;
> }
> #endif
>
> query = (ngx_resolver_hdr_t *) p;
>
> - ident = ngx_random();
> -
> - ngx_log_debug2(NGX_LOG_DEBUG_CORE, r->log, 0,
> - "resolve: \"%V\" A %i", name, ident & 0xffff);
> -
> - query->ident_hi = (u_char) ((ident >> 8) & 0xff);
> - query->ident_lo = (u_char) (ident & 0xff);
> + if (r->ipv4) {
> + ident = ngx_random();
> +
> + ngx_log_debug2(NGX_LOG_DEBUG_CORE, r->log, 0,
> + "resolve: \"%V\" A %i", name, ident & 0xffff);
> +
> + query->ident_hi = (u_char) ((ident >> 8) & 0xff);
> + query->ident_lo = (u_char) (ident & 0xff);
> + }
>
> /* recursion query */
> query->flags_hi = 1; query->flags_lo = 0;
> @@ -3731,7 +3766,9 @@ ngx_resolver_create_name_query(ngx_resol
>
> p = rn->query6;
>
> - ngx_memcpy(p, rn->query, rn->qlen);
> + if (r->ipv4) {
> + ngx_memcpy(p, rn->query, rn->qlen);
> + }
>
> query = (ngx_resolver_hdr_t *) p;
>
> diff -r fecd73db563f -r 04e314eb6b4d src/core/ngx_resolver.h
> --- a/src/core/ngx_resolver.h Tue Jun 21 17:25:37 2022 +0300
> +++ b/src/core/ngx_resolver.h Wed Feb 23 07:08:37 2022 +0300
> @@ -175,8 +175,10 @@ struct ngx_resolver_s {
> ngx_queue_t srv_expire_queue;
> ngx_queue_t addr_expire_queue;
>
> + unsigned ipv4:1;
> +
> #if (NGX_HAVE_INET6)
> - ngx_uint_t ipv6; /* unsigned ipv6:1; */
> + unsigned ipv6:1;
> ngx_rbtree_t addr6_rbtree;
> ngx_rbtree_node_t addr6_sentinel;
> ngx_queue_t addr6_resend_queue;
# HG changeset patch
# User Sergey Kandaurov <pluknet at nginx.com>
# Date 1657724523 -14400
# Wed Jul 13 19:02:03 2022 +0400
# Node ID 61fa6c872c85b54ce41af8748ffde933dbaae47e
# Parent 2a77754cd9feae752152e8eef7e5c506dd0186d6
Resolver: fixed memory leak for the "ipv4=off" case.
This change partially reverts 2a77754cd9fe to properly free rn->query.
diff -r 2a77754cd9fe -r 61fa6c872c85 src/core/ngx_resolver.c
--- a/src/core/ngx_resolver.c Tue Jul 12 21:44:02 2022 +0400
+++ b/src/core/ngx_resolver.c Wed Jul 13 19:02:03 2022 +0400
@@ -1290,7 +1290,7 @@ ngx_resolver_send_query(ngx_resolver_t *
rec->log.action = "resolving";
}
- if (rn->query && rn->naddrs == (u_short) -1) {
+ if (rn->naddrs == (u_short) -1) {
rc = rn->tcp ? ngx_resolver_send_tcp_query(r, rec, rn->query, rn->qlen)
: ngx_resolver_send_udp_query(r, rec, rn->query, rn->qlen);
@@ -1792,13 +1792,10 @@ ngx_resolver_process_response(ngx_resolv
q = ngx_queue_next(q))
{
rn = ngx_queue_data(q, ngx_resolver_node_t, queue);
-
- if (rn->query) {
- qident = (rn->query[0] << 8) + rn->query[1];
-
- if (qident == ident) {
- goto dns_error_name;
- }
+ qident = (rn->query[0] << 8) + rn->query[1];
+
+ if (qident == ident) {
+ goto dns_error_name;
}
#if (NGX_HAVE_INET6)
@@ -3684,10 +3681,7 @@ ngx_resolver_create_name_query(ngx_resol
}
rn->qlen = (u_short) len;
-
- if (r->ipv4) {
- rn->query = p;
- }
+ rn->query = p;
#if (NGX_HAVE_INET6)
if (r->ipv6) {
--
Sergey Kandaurov
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