Daemon supports forward-DNS lookups for simple hostnames

in hosts deny/allow config settings.

5 files changed, 72 insertions, 27 deletions

diff --git a/NEWS b/NEWS
index d116f9b9..5fd125af 100644
--- a/NEWS
+++ b/NEWS
@@ -77,6 +77,9 @@ Changes since 3.0.4:
     - Added the "reverse lookup" parameter to the rsync daemon config file to
       allow reverse-DNS lookups to be disabled.
 
+    - Added a forward-DNS lookup for the daemon's hosts allow/deny config.  Can
+      be disabled via "forward lookup" parameter (defaults to enabled).
+
     - Added a way for more than one group to be specified in the daemon's
       config file, including a way to specify that you want all of the
       specified user's groups without having to name them.  Also changed the
diff --git a/access.c b/access.c
index 9a023dec..367fd447 100644
--- a/access.c
+++ b/access.c
@@ -20,11 +20,47 @@
 
 #include "rsync.h"
 
-static int match_hostname(const char *host, const char *tok)
+static int allow_forward_dns;
+
+extern const char undetermined_hostname[];
+
+static int match_hostname(const char **host_ptr, const char *addr, const char *tok)
 {
+	struct hostent *hp;
+	unsigned int i;
+	const char *host = *host_ptr;
+
 	if (!host || !*host)
 		return 0;
-	return iwildmatch(tok, host);
+
+	/* First check if the reverse-DNS-determined hostname matches. */
+	if (iwildmatch(tok, host))
+		return 1;
+
+	if (!allow_forward_dns)
+		return 0;
+
+	/* Fail quietly if tok is an address or wildcarded entry, not a simple hostname. */
+	if (!tok[strspn(tok, ".0123456789")] || tok[strcspn(tok, ":/*?[")])
+		return 0;
+
+	/* Now try forward-DNS on the token (config-specified hostname) and see if the IP matches. */
+	if (!(hp = gethostbyname(tok)))
+		return 0;
+
+	for (i = 0; hp->h_addr_list[i] != NULL; i++) {
+		if (strcmp(addr, inet_ntoa(*(struct in_addr*)(hp->h_addr_list[i]))) == 0) {
+			/* If reverse lookups are off, we'll use the conf-specified
+			 * hostname in preference to UNDETERMINED. */
+			if (host == undetermined_hostname) {
+				if (!(*host_ptr = strdup(tok)))
+					*host_ptr = undetermined_hostname;
+			}
+			return 1;
+		}
+	}
+
+	return 0;
 }
 
 static int match_binary(const char *b1, const char *b2, const char *mask, int addrlen)
@@ -70,24 +106,16 @@ static int match_address(const char *addr, const char *tok)
 #endif
 	char mask[16];
 	char *a = NULL, *t = NULL;
-	unsigned int len;
 
 	if (!addr || !*addr)
 		return 0;
 
 	p = strchr(tok,'/');
-	if (p) {
+	if (p)
 		*p = '\0';
-		len = p - tok;
-	} else
-		len = strlen(tok);
 
-	/* Fail quietly if tok is a hostname (not an address) */
-	if (strspn(tok, ".0123456789") != len
-#ifdef INET6
-	    && strchr(tok, ':') == NULL
-#endif
-	) {
+	/* Fail quietly if tok is a hostname, not an address. */
+	if (tok[strspn(tok, ".0123456789")] && strchr(tok, ':') == NULL) {
 		if (p)
 			*p = '/';
 		return 0;
@@ -210,7 +238,7 @@ static int match_address(const char *addr, const char *tok)
 	return ret;
 }
 
-static int access_match(const char *list, const char *addr, const char *host)
+static int access_match(const char *list, const char *addr, const char **host_ptr)
 {
 	char *tok;
 	char *list2 = strdup(list);
@@ -221,7 +249,7 @@ static int access_match(const char *list, const char *addr, const char *host)
 	strlower(list2);
 
 	for (tok = strtok(list2, " ,\t"); tok; tok = strtok(NULL, " ,\t")) {
-		if (match_hostname(host, tok) || match_address(addr, tok)) {
+		if (match_hostname(host_ptr, addr, tok) || match_address(addr, tok)) {
 			free(list2);
 			return 1;
 		}
@@ -231,17 +259,21 @@ static int access_match(const char *list, const char *addr, const char *host)
 	return 0;
 }
 
-int allow_access(const char *addr, const char *host,
-		 const char *allow_list, const char *deny_list)
+int allow_access(const char *addr, const char **host_ptr, int i)
 {
+	const char *allow_list = lp_hosts_allow(i);
+	const char *deny_list = lp_hosts_deny(i);
+
 	if (allow_list && !*allow_list)
 		allow_list = NULL;
 	if (deny_list && !*deny_list)
 		deny_list = NULL;
 
+	allow_forward_dns = lp_forward_lookup(i);
+
 	/* If we match an allow-list item, we always allow access. */
 	if (allow_list) {
-		if (access_match(allow_list, addr, host))
+		if (access_match(allow_list, addr, host_ptr))
 			return 1;
 		/* For an allow-list w/o a deny-list, disallow non-matches. */
 		if (!deny_list)
@@ -250,7 +282,7 @@ int allow_access(const char *addr, const char *host,
 
 	/* If we match a deny-list item (and got past any allow-list
 	 * items), we always disallow access. */
-	if (deny_list && access_match(deny_list, addr, host))
+	if (deny_list && access_match(deny_list, addr, host_ptr))
 		return 0;
 
 	/* Allow all other access. */
diff --git a/clientserver.c b/clientserver.c
index 21ef01c5..8b6b896f 100644
--- a/clientserver.c
+++ b/clientserver.c
@@ -515,7 +515,7 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
 	set_env_str("RSYNC_HOST_NAME", host);
 	set_env_str("RSYNC_HOST_ADDR", addr);
 
-	if (!allow_access(addr, host, lp_hosts_allow(i), lp_hosts_deny(i))) {
+	if (!allow_access(addr, &host, i)) {
 		rprintf(FLOG, "rsync denied on module %s from %s (%s)\n",
 			name, host, addr);
 		if (!lp_list(i))
diff --git a/loadparm.c b/loadparm.c
index 10c33455..792c3dad 100644
--- a/loadparm.c
+++ b/loadparm.c
@@ -139,6 +139,7 @@ typedef struct {
 	int timeout;
 
 	BOOL fake_super;
+	BOOL forward_lookup;
 	BOOL ignore_errors;
 	BOOL ignore_nonreadable;
 	BOOL list;
@@ -211,6 +212,7 @@ static const all_vars Defaults = {
  /* timeout; */			0,
 
  /* fake_super; */		False,
+ /* forward_lookup; */		True,
  /* ignore_errors; */		False,
  /* ignore_nonreadable; */	False,
  /* list; */			True,
@@ -322,6 +324,7 @@ static struct parm_struct parm_table[] =
  {"exclude",           P_STRING, P_LOCAL, &Vars.l.exclude,             NULL,0},
  {"fake super",        P_BOOL,   P_LOCAL, &Vars.l.fake_super,          NULL,0},
  {"filter",            P_STRING, P_LOCAL, &Vars.l.filter,              NULL,0},
+ {"forward lookup",    P_BOOL,   P_LOCAL, &Vars.l.forward_lookup,      NULL,0},
  {"gid",               P_STRING, P_LOCAL, &Vars.l.gid,                 NULL,0},
  {"hosts allow",       P_STRING, P_LOCAL, &Vars.l.hosts_allow,         NULL,0},
  {"hosts deny",        P_STRING, P_LOCAL, &Vars.l.hosts_deny,          NULL,0},
@@ -476,6 +479,7 @@ FN_LOCAL_INTEGER(lp_syslog_facility, syslog_facility)
 FN_LOCAL_INTEGER(lp_timeout, timeout)
 
 FN_LOCAL_BOOL(lp_fake_super, fake_super)
+FN_LOCAL_BOOL(lp_forward_lookup, forward_lookup)
 FN_LOCAL_BOOL(lp_ignore_errors, ignore_errors)
 FN_LOCAL_BOOL(lp_ignore_nonreadable, ignore_nonreadable)
 FN_LOCAL_BOOL(lp_list, list)
diff --git a/rsyncd.conf.yo b/rsyncd.conf.yo
index f96fc9e1..2dbf67c5 100644
--- a/rsyncd.conf.yo
+++ b/rsyncd.conf.yo
@@ -532,13 +532,14 @@ quote(itemization(
   IP address and maskaddr is the netmask in dotted decimal notation for IPv4,
   or similar for IPv6, e.g. ffff:ffff:ffff:ffff:: instead of /64. All IP
   addresses which match the masked IP address will be allowed in.
-  it() a hostname. The hostname as determined by a reverse lookup will
-  be matched (case insensitive) against the pattern. Only an exact
-  match is allowed in.  This only works if "reverse lookup" is enabled
-  (the default).
-  it() a hostname pattern using wildcards. These are matched using the
-  same rules as normal unix filename matching. If the pattern matches
-  then the client is allowed in.
+  it() a hostname pattern using wildcards. If the hostname of the connecting IP
+  (as determined by a reverse lookup) matches the wildcarded name (using the
+  same rules as normal unix filename matching), the client is allowed in.  This
+  only works if "reverse lookup" is enabled (the default).
+  it() a hostname. A plain hostname is matched against the reverse DNS of the
+  connecting IP (if "reverse lookup" is enabled), and/or the IP of the given
+  hostname is matched against the connecting IP (if "forward lookup" is
+  enabled, as it is by default).  Any match will be allowed in.
 ))
 
 Note IPv6 link-local addresses can have a scope in the address specification:
@@ -578,6 +579,11 @@ lookup as soon as a client connects, so disabling it for a module will not
 avoid the lookup.  Thus, you probably want to disable it globally and then
 enable it for modules that need the information.
 
+dit(bf(forward lookup)) Controls whether the daemon performs a forward lookup
+on any hostname specified in an hosts allow/deny setting.  By default this is
+enabled, allowing the use of an explicit hostname that would not be returned
+by reverse DNS of the connecting IP.
+
 dit(bf(ignore errors)) This parameter tells rsyncd to
 ignore I/O errors on the daemon when deciding whether to run the delete
 phase of the transfer. Normally rsync skips the bf(--delete) step if any