s4:libcli/resolve: add getaddrinfo()/dns_looup() resolving

This "dns_ex" module provides flexible lookup methods
for dns lookups.

The getaddrinfo() part looks at /etc/hosts and dns.
As it handles CNAME replies badly we fallback
to use dns_lookup(name, "A").

The dns_lookup() makes DNS SRV lookups possible.

This module is not a real resolve module, it's just
a generic helper as the nbtlist.c code is.

The next step will be that the "host" module will
use the dns_ex.c code.

metze

1 files changed, 484 insertions, 0 deletions

diff --git a/source4/libcli/resolve/dns_ex.c b/source4/libcli/resolve/dns_ex.c
new file mode 100644
index 0000000000..4bcf50a014
--- /dev/null
+++ b/source4/libcli/resolve/dns_ex.c
@@ -0,0 +1,484 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   async getaddrinfo()/dns_lookup() name resolution module
+
+   Copyright (C) Andrew Tridgell 2005
+   Copyright (C) Stefan Metzmacher 2008
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/*
+  this module uses a fork() per getaddrinfo() or dns_looup() call.
+  At first that might seem crazy, but it is actually very fast,
+  and solves many of the tricky problems of keeping a child
+  hanging around in a librar (like what happens when the parent forks).
+  We use a talloc destructor to ensure that the child is cleaned up
+  when we have finished with this name resolution.
+*/
+
+#include "includes.h"
+#include "lib/events/events.h"
+#include "system/network.h"
+#include "system/filesys.h"
+#include "lib/socket/socket.h"
+#include "libcli/composite/composite.h"
+#include "librpc/gen_ndr/ndr_nbt.h"
+#include "libcli/resolve/resolve.h"
+#include "heimdal/lib/roken/resolve.h"
+
+struct dns_ex_state {
+	bool do_getaddrinfo;
+	bool do_fallback;
+	bool do_srv;
+	struct nbt_name name;
+	struct socket_address **addrs;
+	pid_t child;
+	int child_fd;
+	struct fd_event *fde;
+	struct event_context *event_ctx;
+};
+
+/*
+  kill off a wayward child if needed. This allows us to stop an async
+  name resolution without leaving a potentially blocking call running
+  in a child
+*/
+static int dns_ex_destructor(struct dns_ex_state *state)
+{
+	int status;
+
+	kill(state->child, SIGTERM);
+	close(state->child_fd);
+	if (waitpid(state->child, &status, WNOHANG) == 0) {
+		kill(state->child, SIGKILL);
+		waitpid(state->child, &status, 0);
+	}
+
+	return 0;
+}
+
+/*
+  the blocking child
+*/
+static void run_child_dns_lookup(struct dns_ex_state *state, int fd)
+{
+	struct dns_reply *reply;
+	struct resource_record *rr;
+	uint32_t count = 0;
+	uint32_t srv_valid = 0;
+	struct resource_record **srv_rr;
+	uint32_t addrs_valid = 0;
+	struct resource_record **addrs_rr;
+	char *addrs;
+	bool first;
+	uint32_t i;
+
+	/* this is the blocking call we are going to lots of trouble
+	   to avoid in the parent */
+	reply = dns_lookup(state->name.name, state->do_srv?"SRV":"A");
+	if (!reply) {
+		goto done;
+	}
+
+	if (state->do_srv) {
+		dns_srv_order(reply);
+	}
+
+	/* Loop over all returned records and pick the "srv" records */
+	for (rr=reply->head; rr; rr=rr->next) {
+		/* we are only interested in the IN class */
+		if (rr->class != C_IN) {
+			continue;
+		}
+
+		if (state->do_srv) {
+			/* we are only interested in SRV records */
+			if (rr->type != T_SRV) {
+				continue;
+			}
+
+			/* verify we actually have a SRV record here */
+			if (!rr->u.srv) {
+				continue;
+			}
+
+			/* Verify we got a port */
+			if (rr->u.srv->port == 0) {
+				continue;
+			}
+		} else {
+			/* we are only interested in A records */
+			/* TODO: add AAAA support */
+			if (rr->type != T_A) {
+				continue;
+			}
+
+			/* verify we actually have a A record here */
+			if (!rr->u.a) {
+				continue;
+			}
+		}
+		count++;
+	}
+
+	if (count == 0) {
+		goto done;
+	}
+
+	srv_rr = talloc_zero_array(state,
+				   struct resource_record *,
+				   count);
+	if (!srv_rr) {
+		goto done;
+	}
+
+	addrs_rr = talloc_zero_array(state,
+				     struct resource_record *,
+				     count);
+	if (!addrs_rr) {
+		goto done;
+	}
+
+	/* Loop over all returned records and pick the records */
+	for (rr=reply->head;rr;rr=rr->next) {
+		/* we are only interested in the IN class */
+		if (rr->class != C_IN) {
+			continue;
+		}
+
+		if (state->do_srv) {
+			/* we are only interested in SRV records */
+			if (rr->type != T_SRV) {
+				continue;
+			}
+
+			/* verify we actually have a srv record here */
+			if (!rr->u.srv) {
+				continue;
+			}
+
+			/* Verify we got a port */
+			if (rr->u.srv->port == 0) {
+				continue;
+			}
+
+			srv_rr[srv_valid] = rr;
+			srv_valid++;
+		} else {
+			/* we are only interested in A records */
+			/* TODO: add AAAA support */
+			if (rr->type != T_A) {
+				continue;
+			}
+
+			/* verify we actually have a A record here */
+			if (!rr->u.a) {
+				continue;
+			}
+
+			addrs_rr[addrs_valid] = rr;
+			addrs_valid++;
+		}
+	}
+
+	for (i=0; i < srv_valid; i++) {
+		for (rr=reply->head;rr;rr=rr->next) {
+
+			if (rr->class != C_IN) {
+				continue;
+			}
+
+			/* we are only interested in SRV records */
+			if (rr->type != T_A) {
+				continue;
+			}
+
+			/* verify we actually have a srv record here */
+			if (strcmp(&srv_rr[i]->u.srv->target[0], rr->domain) != 0) {
+				continue;
+			}
+
+			addrs_rr[i] = rr;
+			addrs_valid++;
+			break;
+		}
+	}
+
+	if (addrs_valid == 0) {
+		goto done;
+	}
+
+	addrs = talloc_strdup(state, "");
+	if (!addrs) {
+		goto done;
+	}
+	first = true;
+	for (i=0; i < count; i++) {
+		if (!addrs_rr[i]) {
+			continue;
+		}
+		addrs = talloc_asprintf_append_buffer(addrs, "%s%s:%u",
+						      first?"":",",
+						      inet_ntoa(*addrs_rr[i]->u.a),
+						      srv_rr[i]?srv_rr[i]->u.srv->port:0);
+		if (!addrs) {
+			goto done;
+		}
+		first = false;
+	}
+
+	if (addrs) {
+		write(fd, addrs, talloc_get_size(addrs));
+	}
+
+done:
+	close(fd);
+}
+
+/*
+  the blocking child
+*/
+static void run_child_getaddrinfo(struct dns_ex_state *state, int fd)
+{
+	int ret;
+	struct addrinfo hints;
+	struct addrinfo *res;
+	struct addrinfo *res_list = NULL;
+	char *addrs;
+	bool first;
+
+	ZERO_STRUCT(hints);
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_family = AF_INET;/* TODO: add AF_INET6 support */
+	hints.ai_flags = AI_ADDRCONFIG | AI_NUMERICSERV;
+
+	ret = getaddrinfo(state->name.name, "0", &hints, &res_list);
+	if (ret == EAI_NODATA && state->do_fallback) {
+		/* getaddrinfo() doesn't handle CNAME records */
+		run_child_dns_lookup(state, fd);
+		return;
+	}
+	if (ret != 0) {
+		goto done;
+	}
+
+	addrs = talloc_strdup(state, "");
+	if (!addrs) {
+		goto done;
+	}
+	first = true;
+	for (res = res_list; res; res = res->ai_next) {
+		struct sockaddr_in *in;
+
+		if (res->ai_family != AF_INET) {
+			continue;
+		}
+		in = (struct sockaddr_in *)res->ai_addr;
+
+		addrs = talloc_asprintf_append_buffer(addrs, "%s%s:%u",
+						      first?"":",",
+						      inet_ntoa(in->sin_addr),
+						      0);
+		if (!addrs) {
+			goto done;
+		}
+		first = false;
+	}
+
+	if (addrs) {
+		write(fd, addrs, talloc_get_size(addrs));
+	}
+done:
+	if (res_list) {
+		freeaddrinfo(res_list);
+	}
+	close(fd);
+}
+
+/*
+  handle a read event on the pipe
+*/
+static void pipe_handler(struct event_context *ev, struct fd_event *fde, 
+			 uint16_t flags, void *private_data)
+{
+	struct composite_context *c = talloc_get_type(private_data, struct composite_context);
+	struct dns_ex_state *state = talloc_get_type(c->private_data,
+				     struct dns_ex_state);
+	char address[2048];
+	uint32_t num_addrs, i;
+	char **addrs;
+	int ret;
+	int status;
+
+	/* if we get any event from the child then we know that we
+	   won't need to kill it off */
+	talloc_set_destructor(state, NULL);
+
+	/* yes, we don't care about EAGAIN or other niceities
+	   here. They just can't happen with this parent/child
+	   relationship, and even if they did then giving an error is
+	   the right thing to do */
+	ret = read(state->child_fd, address, sizeof(address)-1);
+	close(state->child_fd);
+	if (waitpid(state->child, &status, WNOHANG) == 0) {
+		kill(state->child, SIGKILL);
+		waitpid(state->child, &status, 0);
+	}
+
+	if (ret <= 0) {
+		composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
+		return;
+	}
+
+	/* enusre the address looks good */
+	address[ret] = 0;
+
+	addrs = str_list_make(state, address, ",");
+	if (composite_nomem(addrs, c)) return;
+
+	num_addrs = str_list_length((const char * const *)addrs);
+
+	state->addrs = talloc_array(state, struct socket_address *,
+				    num_addrs+1);
+	if (composite_nomem(state->addrs, c)) return;
+
+	for (i=0; i < num_addrs; i++) {
+		uint32_t port = 0;
+		char *p = strrchr(addrs[i], ':');
+
+		if (!p) {
+			composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
+			return;
+		}
+
+		*p = '\0';
+		p++;
+
+		if (strcmp(addrs[i], "0.0.0.0") == 0 ||
+		    inet_addr(addrs[i]) == INADDR_NONE) {
+			composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
+			return;
+		}
+		port = strtoul(p, NULL, 10);
+		if (port > UINT16_MAX) {
+			port = 0;
+		}
+		state->addrs[i] = socket_address_from_strings(state->addrs,
+							      "ipv4",
+							      addrs[i],
+							      port);
+		if (composite_nomem(state->addrs[i], c)) return;
+	}
+	state->addrs[i] = NULL;
+
+	composite_done(c);
+}
+
+/*
+  getaddrinfo() or dns_lookup() name resolution method - async send
+ */
+struct composite_context *resolve_name_dns_ex_send(TALLOC_CTX *mem_ctx,
+						   struct event_context *event_ctx,
+						   void *privdata,
+						   struct nbt_name *name,
+						   bool do_getaddrinfo,
+						   bool do_fallback,
+						   bool do_srv)
+{
+	struct composite_context *c;
+	struct dns_ex_state *state;
+	int fd[2] = { -1, -1 };
+	int ret;
+
+	c = composite_create(mem_ctx, event_ctx);
+	if (c == NULL) return NULL;
+
+	if (composite_nomem(c->event_ctx, c)) return c;
+
+	state = talloc_zero(c, struct dns_ex_state);
+	if (composite_nomem(state, c)) return c;
+	c->private_data = state;
+
+	c->status = nbt_name_dup(state, name, &state->name);
+	if (!composite_is_ok(c)) return c;
+
+	/* setup a pipe to chat to our child */
+	ret = pipe(fd);
+	if (ret == -1) {
+		composite_error(c, map_nt_error_from_unix(errno));
+		return c;
+	}
+
+	state->do_getaddrinfo = do_getaddrinfo;
+	state->do_fallback = do_fallback;
+	state->do_srv = do_srv;
+
+	state->child_fd = fd[0];
+	state->event_ctx = c->event_ctx;
+
+	/* we need to put the child in our event context so
+	   we know when the dns_lookup() has finished */
+	state->fde = event_add_fd(c->event_ctx, c, state->child_fd, EVENT_FD_READ, 
+				  pipe_handler, c);
+	if (composite_nomem(state->fde, c)) {
+		close(fd[0]);
+		close(fd[1]);
+		return c;
+	}
+
+	state->child = fork();
+	if (state->child == (pid_t)-1) {
+		composite_error(c, map_nt_error_from_unix(errno));
+		return c;
+	}
+
+	if (state->child == 0) {
+		close(fd[0]);
+		if (state->do_getaddrinfo) {
+			run_child_getaddrinfo(state, fd[1]);
+		} else {
+			run_child_dns_lookup(state, fd[1]);
+		}
+		_exit(0);
+	}
+	close(fd[1]);
+
+	/* cleanup wayward children */
+	talloc_set_destructor(state, dns_ex_destructor);
+
+	return c;
+}
+
+/*
+  getaddrinfo() or dns_lookup() name resolution method - recv side
+*/
+NTSTATUS resolve_name_dns_ex_recv(struct composite_context *c, 
+				  TALLOC_CTX *mem_ctx,
+				  struct socket_address ***addrs)
+{
+	NTSTATUS status;
+
+	status = composite_wait(c);
+
+	if (NT_STATUS_IS_OK(status)) {
+		struct dns_ex_state *state = talloc_get_type(c->private_data,
+					     struct dns_ex_state);
+		*addrs = talloc_steal(mem_ctx, state->addrs);
+	}
+
+	talloc_free(c);
+	return status;
+}