Backport of:

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 ++
 docs/manual/mod/core.xml                   | 12 +++++++++---
 server/core.c                              |  9 +++++++++
 server/util.c                              |  8 ++++++--
 server/util_xml.c                          |  2 +-
 5 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/docs/manual/mod/core.xml b/docs/manual/mod/core.xml
#index 428205b8c29..46cacd88293 100644
#--- a/docs/manual/mod/core.xml
#+++ b/docs/manual/mod/core.xml
#@@ -3014,13 +3014,19 @@ LimitRequestLine 4094
# <override>All</override>
# 
# <usage>
#-    <p>Limit (in bytes) on maximum size of an XML-based request
#-    body. A value of <code>0</code> will disable any checking.</p>
#+    <p>Limit (in bytes) on the maximum size of an XML-based request
#+    body. A value of <code>0</code> will apply a hard limit (depending on
#+    32bit vs 64bit system) allowing for XML escaping within the bounds of
#+    the system addressable memory, but it exists for compatibility only
#+    and is not recommended since it does not account for memory consumed
#+    elsewhere or concurrent requests, which might result in an overall
#+    system out-of-memory.
# 
#     <p>Example:</p>
# 
#     <highlight language="config">
#-LimitXMLRequestBody 0
#+# Limit of 1 MiB
#+LimitXMLRequestBody 1073741824
#     </highlight>
# 
# </usage>
--- a/server/core.c
+++ b/server/core.c
@@ -66,6 +66,8 @@
 /* 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)
 
@@ -3654,6 +3656,11 @@ static const char *set_limit_xml_req_bod
     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;
 }
 
@@ -3742,6 +3749,8 @@ AP_DECLARE(apr_size_t) ap_get_limit_xml_
     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;
 }
--- a/server/util.c
+++ b/server/util.c
@@ -2037,11 +2037,14 @@ AP_DECLARE(char *) ap_escape_urlencoded(
 
 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] == '&')
@@ -2050,6 +2053,7 @@ AP_DECLARE(char *) ap_escape_html2(apr_p
             j += 5;
         else if (toasc && !apr_isascii(s[i]))
             j += 5;
+    }
 
     if (j == 0)
         return apr_pstrmemdup(p, s, i);
--- a/server/util_xml.c
+++ b/server/util_xml.c
@@ -85,7 +85,7 @@ AP_DECLARE(int) ap_xml_parse_input(reque
             }
 
             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);
