From be0a01bdb83395d9f3a5ea09c1308a4f1a972cbd Mon Sep 17 00:00:00 2001
From: Matthew Garrett <mjg59@srcf.ucam.org>
Date: Tue, 23 Feb 2016 13:53:20 -0800
Subject: [PATCH] Don't allow unhandled POSTs to write to the filesystem by
 default

If there's no registered handler for a POST request, the default behaviour
is to write it to the filesystem. Several million deployed devices appear
to have this behaviour, making it possible to (at least) store arbitrary
data on them. Add a configure option that enables this behaviour, and change
the default to just drop POSTs that aren't directly handled.
---
 configure.ac                         | 4 ++++
 upnp/inc/upnpconfig.h.in             | 5 +++++
 upnp/src/genlib/net/http/webserver.c | 4 ++++
 3 files changed, 13 insertions(+)

diff --git a/configure.ac b/configure.ac
index dd88734..ea2bc09 100644
--- a/configure.ac
+++ b/configure.ac
@@ -482,6 +482,10 @@ if test "x$enable_scriptsupport" = xyes ; then
         AC_DEFINE(UPNP_ENABLE_BLOCKING_TCP_CONNECTIONS, 1, [see upnpconfig.h])
 fi
 
+RT_BOOL_ARG_ENABLE([postwrite], [no], [write to the filesystem on otherwise unhandled POST requests])
+if test "x$enable_postwrite" = xyes ; then
+        AC_DEFINE(UPNP_ENABLE_POST_WRITE, 1, [see upnpconfig.h])
+fi
 
 RT_BOOL_ARG_ENABLE([samples], [yes], [compilation of upnp/sample/ code])
 
diff --git a/upnp/inc/upnpconfig.h.in b/upnp/inc/upnpconfig.h.in
index 46ddc6e..5df8c5a 100644
--- a/upnp/inc/upnpconfig.h.in
+++ b/upnp/inc/upnpconfig.h.in
@@ -135,5 +135,10 @@
  * header (i.e. configure --enable-unspecified_server) */
 #undef UPNP_ENABLE_UNSPECIFIED_SERVER
 
+/** Defined to 1 if the library has been compiled to support filesystem writes on POST
+ *  (i.e. configure --enable-postwrite) */
+#undef UPNP_ENABLE_POST_WRITE
+
+
 #endif /* UPNP_CONFIG_H */
 
diff --git a/upnp/src/genlib/net/http/webserver.c b/upnp/src/genlib/net/http/webserver.c
index 8991c16..8b2ecf2 100644
--- a/upnp/src/genlib/net/http/webserver.c
+++ b/upnp/src/genlib/net/http/webserver.c
@@ -1369,9 +1369,13 @@ static int http_RecvPostMessage(
 		if (Fp == NULL)
 			return HTTP_INTERNAL_SERVER_ERROR;
 	} else {
+#ifdef UPNP_ENABLE_POST_WRITE
 		Fp = fopen(filename, "wb");
 		if (Fp == NULL)
 			return HTTP_UNAUTHORIZED;
+#else
+		return HTTP_NOT_FOUND;
+#endif
 	}
 	parser->position = POS_ENTITY;
 	do {