BUG/MAJOR: http: fix breakage of "reqdeny" causing random crashes

Commit 108b1dd ("MEDIUM: http: configurable http result codes for
http-request deny") introduced in 1.6-dev2 was incomplete. It introduced
a new field "rule_deny_status" into struct http_txn, which is filled only
by actions "http-request deny" and "http-request tarpit". It's then used
in the deny code path to emit the proper error message, but is used
uninitialized when the deny comes from a "reqdeny" rule, causing random
behaviours ranging from returning a 200, an empty response, or crashing
the process. Often upon startup only 200 was returned but after the fields
are used the crash happens. This can be sped up using -dM.

There's no need at all for storing this status in the http_txn struct
anyway since it's used immediately after being set. Let's store it in
a temporary variable instead which is passed as an argument to function
http_req_get_intercept_rule().

As an extra benefit, removing it from struct http_txn reduced the size
of this struct by 8 bytes.

This fix must be backported to 1.6 where the bug was detected. Special
thanks to Falco Schmutz for his detailed report including an exploitable
core and a reproducer.

diff --git a/include/types/proto_http.h b/include/types/proto_http.h
index 7e8f2cbbcad91d6da49f5e64b2b8412708102885..935be8ce6655f6708c86e9551b468940ede60bf2 100644 (file)
--- a/include/types/proto_http.h
+++ b/include/types/proto_http.h
@@ -366,7 +366,6 @@ struct http_txn {
        unsigned int flags;             /* transaction flags */
        enum http_meth_t meth;          /* HTTP method */
        /* 1 unused byte here */
-       short rule_deny_status;         /* HTTP status from rule when denying */
        short status;                   /* HTTP status from the server, negative if from proxy */
 
        char *uri;                      /* first line if log needed, NULL otherwise */

diff --git a/src/proto_http.c b/src/proto_http.c
index 416504247a8df068eef2dcc4325e959b906de41e..d79a7821936863abb34c7d402284cb7754e8b881 100644 (file)
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -3276,10 +3276,12 @@ static int http_transform_header(struct stream* s, struct http_msg *msg,
  * further processing of the request (auth, deny, ...), and defaults to
  * HTTP_RULE_RES_STOP if it executed all rules or stopped on an allow, or
  * HTTP_RULE_RES_CONT if the last rule was reached. It may set the TX_CLTARPIT
- * on txn->flags if it encounters a tarpit rule.
+ * on txn->flags if it encounters a tarpit rule. If <deny_status> is not NULL
+ * and a deny/tarpit rule is matched, it will be filled with this rule's deny
+ * status.
  */
 enum rule_result
-http_req_get_intercept_rule(struct proxy *px, struct list *rules, struct stream *s)
+http_req_get_intercept_rule(struct proxy *px, struct list *rules, struct stream *s, int *deny_status)
 {
        struct session *sess = strm_sess(s);
        struct http_txn *txn = s->txn;
@@ -3325,12 +3327,14 @@ resume_execution:
                        return HTTP_RULE_RES_STOP;
 
                case ACT_ACTION_DENY:
-                       txn->rule_deny_status = rule->deny_status;
+                       if (deny_status)
+                               *deny_status = rule->deny_status;
                        return HTTP_RULE_RES_DENY;
 
                case ACT_HTTP_REQ_TARPIT:
                        txn->flags |= TX_CLTARPIT;
-                       txn->rule_deny_status = rule->deny_status;
+                       if (deny_status)
+                               *deny_status = rule->deny_status;
                        return HTTP_RULE_RES_DENY;
 
                case ACT_HTTP_REQ_AUTH:
@@ -4090,6 +4094,7 @@ int http_process_req_common(struct stream *s, struct channel *req, int an_bit, s
        struct redirect_rule *rule;
        struct cond_wordlist *wl;
        enum rule_result verdict;
+       int deny_status = HTTP_ERR_403;
 
        if (unlikely(msg->msg_state < HTTP_MSG_BODY)) {
                /* we need more data */
@@ -4110,7 +4115,7 @@ int http_process_req_common(struct stream *s, struct channel *req, int an_bit, s
 
        /* evaluate http-request rules */
        if (!LIST_ISEMPTY(&px->http_req_rules)) {
-               verdict = http_req_get_intercept_rule(px, &px->http_req_rules, s);
+               verdict = http_req_get_intercept_rule(px, &px->http_req_rules, s, &deny_status);
 
                switch (verdict) {
                case HTTP_RULE_RES_YIELD: /* some data miss, call the function later. */
@@ -4156,7 +4161,7 @@ int http_process_req_common(struct stream *s, struct channel *req, int an_bit, s
 
                /* parse the whole stats request and extract the relevant information */
                http_handle_stats(s, req);
-               verdict = http_req_get_intercept_rule(px, &px->uri_auth->http_req_rules, s);
+               verdict = http_req_get_intercept_rule(px, &px->uri_auth->http_req_rules, s, &deny_status);
                /* not all actions implemented: deny, allow, auth */
 
                if (verdict == HTTP_RULE_RES_DENY) /* stats http-request deny */
@@ -4285,9 +4290,9 @@ int http_process_req_common(struct stream *s, struct channel *req, int an_bit, s
                manage_client_side_cookies(s, req);
 
        txn->flags |= TX_CLDENY;
-       txn->status = http_err_codes[txn->rule_deny_status];
+       txn->status = http_err_codes[deny_status];
        s->logs.tv_request = now;
-       http_reply_and_close(s, txn->status, http_error_message(s, txn->rule_deny_status));
+       http_reply_and_close(s, txn->status, http_error_message(s, deny_status));
        stream_inc_http_err_ctr(s);
        sess->fe->fe_counters.denied_req++;
        if (sess->fe != s->be)