From 5a72f0fe6f2f8ce35c45242e99a421dc19251ab5 Mon Sep 17 00:00:00 2001
From: Yann Ylavic <ylavic@apache.org>
Date: Mon, 7 Mar 2022 14:48:54 +0000
Subject: [PATCH] core: Make sure and check that LimitXMLRequestBody fits in
 system memory.

LimitXMLRequestBody can not exceed the size needed to ap_escape_html2() the
body without failing to allocate memory, so enforce this at load time based
on APR_SIZE_MAX, and make sure that ap_escape_html2() is within the bounds.

Document the limits for LimitXMLRequestBody in our docs.


Merge r1898686 from trunk.
Submitted by: ylavic, rpluem
Reviewed by: ylavic, covener, rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1898693 13f79535-47bb-0310-9956-ffa450edef68
---
 changes-entries/AP_MAX_LIMIT_XML_BODY.diff |  2 ++
 server/core.c                              |  9 +++++++++
 server/util.c                              |  8 ++++++--
 server/util_xml.c                          |  2 +-
 4 files changed, 27 insertions(+), 6 deletions(-)
 create mode 100644 changes-entries/AP_MAX_LIMIT_XML_BODY.diff

diff --git a/changes-entries/AP_MAX_LIMIT_XML_BODY.diff b/changes-entries/AP_MAX_LIMIT_XML_BODY.diff
new file mode 100644
index 00000000000..07fef3c624c
--- /dev/null
+++ b/changes-entries/AP_MAX_LIMIT_XML_BODY.diff
@@ -0,0 +1,2 @@
+  *) core: Make sure and check that LimitXMLRequestBody fits in system memory.
+     [Ruediger Pluem, Yann Ylavic]
\ No newline at end of file
diff --git a/server/core.c b/server/core.c
index 798212b4808..090e3976421 100644
--- a/server/core.c
+++ b/server/core.c
@@ -72,6 +72,8 @@
 /* LimitXMLRequestBody handling */
 #define AP_LIMIT_UNSET                  ((long) -1)
 #define AP_DEFAULT_LIMIT_XML_BODY       ((apr_size_t)1000000)
+/* Hard limit for ap_escape_html2() */
+#define AP_MAX_LIMIT_XML_BODY           ((apr_size_t)(APR_SIZE_MAX / 6 - 1))
 
 #define AP_MIN_SENDFILE_BYTES           (256)
 
@@ -3761,6 +3763,11 @@ static const char *set_limit_xml_req_body(cmd_parms *cmd, void *conf_,
     if (conf->limit_xml_body < 0)
         return "LimitXMLRequestBody requires a non-negative integer.";
 
+    /* zero is AP_MAX_LIMIT_XML_BODY (implicitly) */
+    if ((apr_size_t)conf->limit_xml_body > AP_MAX_LIMIT_XML_BODY)
+        return apr_psprintf(cmd->pool, "LimitXMLRequestBody must not exceed "
+                            "%" APR_SIZE_T_FMT, AP_MAX_LIMIT_XML_BODY);
+
     return NULL;
 }
 
@@ -3849,6 +3856,8 @@ AP_DECLARE(apr_size_t) ap_get_limit_xml_body(const request_rec *r)
     conf = ap_get_core_module_config(r->per_dir_config);
     if (conf->limit_xml_body == AP_LIMIT_UNSET)
         return AP_DEFAULT_LIMIT_XML_BODY;
+    if (conf->limit_xml_body == 0)
+        return AP_MAX_LIMIT_XML_BODY;
 
     return (apr_size_t)conf->limit_xml_body;
 }
diff --git a/server/util.c b/server/util.c
index 6cfe0035c49..604be1a1ce3 100644
--- a/server/util.c
+++ b/server/util.c
@@ -2142,11 +2142,14 @@ AP_DECLARE(char *) ap_escape_urlencoded(apr_pool_t *p, const char *buffer)
 
 AP_DECLARE(char *) ap_escape_html2(apr_pool_t *p, const char *s, int toasc)
 {
-    int i, j;
+    apr_size_t i, j;
     char *x;
 
     /* first, count the number of extra characters */
-    for (i = 0, j = 0; s[i] != '\0'; i++)
+    for (i = 0, j = 0; s[i] != '\0'; i++) {
+        if (i + j > APR_SIZE_MAX - 6) {
+            abort();
+        }
         if (s[i] == '<' || s[i] == '>')
             j += 3;
         else if (s[i] == '&')
@@ -2155,6 +2158,7 @@ AP_DECLARE(char *) ap_escape_html2(apr_pool_t *p, const char *s, int toasc)
             j += 5;
         else if (toasc && !apr_isascii(s[i]))
             j += 5;
+    }
 
     if (j == 0)
         return apr_pstrmemdup(p, s, i);
diff --git a/server/util_xml.c b/server/util_xml.c
index 4845194656e..22806fa8a40 100644
--- a/server/util_xml.c
+++ b/server/util_xml.c
@@ -85,7 +85,7 @@ AP_DECLARE(int) ap_xml_parse_input(request_rec * r, apr_xml_doc **pdoc)
             }
 
             total_read += len;
-            if (limit_xml_body && total_read > limit_xml_body) {
+            if (total_read > limit_xml_body) {
                 ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(00539)
                               "XML request body is larger than the configured "
                               "limit of %lu", (unsigned long)limit_xml_body);