Add 'deny' as an option for topics/patterns in acl file to allow certain topics to be explicitly denied when they might otherwise be allowed through a more open read/write/readwrite option. Example: 'topic readwrite test/#' and 'topic deny test/hello/#' may be added so that a user can read/write to all test/# topics, except for test/hello/#.

Signed-off-by: Brandt Hill <brandtlarsonhill@gmail.com>

Change variable name for clarity. Remember to initialize bool (I'm bad at C).

Signed-off-by: Brandt Hill <brandtlarsonhill@gmail.com>

Add documentation to config man page

Signed-off-by: Brandt Hill <brandtlarsonhill@gmail.com>

Add test case for deny option

Signed-off-by: Brandt Hill <brandtlarsonhill@gmail.com>

Add deny acls to top of the list to preserve early exit

Signed-off-by: Brandt Hill <brandtlarsonhill@gmail.com>

change comments

Signed-off-by: Brandt Hill <brandtlarsonhill@gmail.com>

man/mosquitto.conf.5.xml

@@ -107,14 +107,16 @@
 						listed will have access. Topic access is added with
 						lines of the format:</para>
 
-					<para><code>topic [read|write|readwrite] &lt;topic&gt;</code></para>
+					<para><code>topic [read|write|readwrite|deny] &lt;topic&gt;</code></para>
 
-					<para>The access type is controlled using "read", "write" or
+					<para>The access type is controlled using "read", "write",
-						"readwrite". This parameter is optional (unless
+						"readwrite" or "deny". This parameter is optional (unless
 						&lt;topic&gt; includes a space character) - if not
 						given then the access is read/write.  &lt;topic&gt; can
 						contain the + or # wildcards as in
-						subscriptions.</para>
+						subscriptions. The "deny" option can used to explicity
+						deny access to a topic that would otherwise be granted
+						by a broader read/write/readwrite statement.</para>
 
 					<para>The first set of topics are applied to anonymous
 						clients, assuming <option>allow_anonymous</option> is
@@ -131,7 +133,7 @@
 						substitution within the topic. The form is the same as
 						for the topic keyword, but using pattern as the
 						keyword.</para>
-					<para><code>pattern [read|write|readwrite] &lt;topic&gt;</code></para>
+					<para><code>pattern [read|write|readwrite|deny] &lt;topic&gt;</code></para>
 
 					<para>The patterns available for substition are:</para>
 					<itemizedlist mark="circle">

src/security_default.c

@@ -217,10 +217,16 @@ int add__acl(struct mosquitto__security_options *security_opts, const char *user
 	/* Add acl to user acl list */
 	if(acl_user->acl){
 		acl_tail = acl_user->acl;
+		if(access == MOSQ_ACL_NONE){
+			/* Put "deny" acls at front of the list */
+			acl->next = acl_tail;
+			acl_user->acl = acl;
+		}else{
 			while(acl_tail->next){
 				acl_tail = acl_tail->next;
 			}
 			acl_tail->next = acl;
+		}
 	}else{
 		acl_user->acl = acl;
 	}
@@ -291,10 +297,16 @@ int add__acl_pattern(struct mosquitto__security_options *security_opts, const ch
 
 	if(security_opts->acl_patterns){
 		acl_tail = security_opts->acl_patterns;
+		if(access == MOSQ_ACL_NONE){
+			/* Put "deny" acls at front of the list */
+			acl->next = acl_tail;
+			security_opts->acl_patterns = acl;
+		}else{
 			while(acl_tail->next){
 				acl_tail = acl_tail->next;
 			}
 			acl_tail->next = acl;
+		}
 	}else{
 		security_opts->acl_patterns = acl;
 	}
@@ -334,7 +346,7 @@ int mosquitto_acl_check_default(struct mosquitto_db *db, struct mosquitto *conte
 		acl_root = NULL;
 	}
 
-	/* Loop through all ACLs for this client. */
+	/* Loop through all ACLs for this client. ACL denials are iterated over first. */
 	while(acl_root){
 		/* Loop through the topic looking for matches to this ACL. */
 
@@ -345,6 +357,10 @@ int mosquitto_acl_check_default(struct mosquitto_db *db, struct mosquitto *conte
 		}
 		mosquitto_topic_matches_sub(acl_root->topic, topic, &result);
 		if(result){
+			if(acl_root->access == MOSQ_ACL_NONE){
+				/* Access was explicitly denied for this topic. */
+				return MOSQ_ERR_ACL_DENIED;
+			}
 			if(access & acl_root->access){
 				/* And access is allowed. */
 				return MOSQ_ERR_SUCCESS;
@@ -374,7 +390,7 @@ int mosquitto_acl_check_default(struct mosquitto_db *db, struct mosquitto *conte
 		}
 	}
 
-	/* Loop through all pattern ACLs. */
+	/* Loop through all pattern ACLs. ACL denial patterns are iterated over first. */
 	if(!context->id) return MOSQ_ERR_ACL_DENIED;
 	clen = strlen(context->id);
 
@@ -418,6 +434,10 @@ int mosquitto_acl_check_default(struct mosquitto_db *db, struct mosquitto *conte
 		mosquitto_topic_matches_sub(local_acl, topic, &result);
 		mosquitto__free(local_acl);
 		if(result){
+			if(acl_root->access == MOSQ_ACL_NONE){
+				/* Access was explicitly denied for this topic pattern. */
+				return MOSQ_ERR_ACL_DENIED;
+			}
 			if(access & acl_root->access){
 				/* And access is allowed. */
 				return MOSQ_ERR_SUCCESS;
@@ -501,6 +521,8 @@ static int aclfile__parse(struct mosquitto_db *db, struct mosquitto__security_op
 						access = MOSQ_ACL_WRITE;
 					}else if(!strcmp(access_s, "readwrite")){
 						access = MOSQ_ACL_READ | MOSQ_ACL_WRITE;
+					}else if(!strcmp(access_s, "deny")){
+						access = MOSQ_ACL_NONE;
 					}else{
 						log__printf(NULL, MOSQ_LOG_ERR, "Error: Invalid topic access type \"%s\" in acl_file \"%s\".", access_s, security_opts->acl_file);
 						mosquitto__free(user);

test/broker/09-acl-access-variants.py

@@ -13,12 +13,15 @@ def write_config(filename, port, per_listener):
 def write_acl(filename, global_en, user_en, pattern_en):
     with open(filename, 'w') as f:
         if global_en:
-            f.write('topic readwrite topic/global\n')
+            f.write('topic readwrite topic/global/#\n')
+            f.write('topic deny      topic/global/except\n')
         if user_en:
             f.write('user username\n')
-            f.write('topic readwrite topic/username\n')
+            f.write('topic readwrite topic/username/#\n')
+            f.write('topic deny      topic/username/except\n')
         if pattern_en:
-            f.write('pattern readwrite pattern/%u\n')
+            f.write('pattern readwrite pattern/%u/#\n')
+            f.write('pattern deny      pattern/%u/except\n')
 
 
 
@@ -73,12 +76,15 @@ def acl_test(port, per_listener, global_en, user_en, pattern_en):
     if global_en:
         single_test(port, per_listener, username=None,       topic="topic/global", expect_deny=False)
         single_test(port, per_listener, username="username", topic="topic/global", expect_deny=True)
+        single_test(port, per_listener, username=None,       topic="topic/global/except", expect_deny=True)
     if user_en:
         single_test(port, per_listener, username=None,       topic="topic/username", expect_deny=True)
         single_test(port, per_listener, username="username", topic="topic/username", expect_deny=False)
+        single_test(port, per_listener, username="username", topic="topic/username/except", expect_deny=True)
     if pattern_en:
         single_test(port, per_listener, username=None,       topic="pattern/username", expect_deny=True)
         single_test(port, per_listener, username="username", topic="pattern/username", expect_deny=False)
+        single_test(port, per_listener, username="username", topic="pattern/username/except", expect_deny=True)
 
 def do_test(port, per_listener):
     try: