Fix security framework bypass

xsltCheckRead and xsltCheckWrite return -1 in case of error but callers
don't check for this condition and allow access. With a specially
crafted URL, xsltCheckRead could be tricked into returning an error
because of a supposedly invalid URL that would still be loaded
succesfully later on.

Fixes #12.

Thanks to Felix Wilhelm for the report.

libxslt/documents.c

@@ -296,10 +296,11 @@ xsltLoadDocument(xsltTransformContextPtr ctxt, const xmlChar *URI) {
 	int res;
 
 	res = xsltCheckRead(ctxt->sec, ctxt, URI);
-	if (res == 0) {
-	    xsltTransformError(ctxt, NULL, NULL,
-		 "xsltLoadDocument: read rights for %s denied\n",
-			     URI);
+	if (res <= 0) {
+            if (res == 0)
+                xsltTransformError(ctxt, NULL, NULL,
+                     "xsltLoadDocument: read rights for %s denied\n",
+                                 URI);
 	    return(NULL);
 	}
     }
@@ -372,10 +373,11 @@ xsltLoadStyleDocument(xsltStylesheetPtr style, const xmlChar *URI) {
 	int res;
 
 	res = xsltCheckRead(sec, NULL, URI);
-	if (res == 0) {
-	    xsltTransformError(NULL, NULL, NULL,
-		 "xsltLoadStyleDocument: read rights for %s denied\n",
-			     URI);
+	if (res <= 0) {
+            if (res == 0)
+                xsltTransformError(NULL, NULL, NULL,
+                     "xsltLoadStyleDocument: read rights for %s denied\n",
+                                 URI);
 	    return(NULL);
 	}
     }

libxslt/imports.c

@@ -130,10 +130,11 @@ xsltParseStylesheetImport(xsltStylesheetPtr style, xmlNodePtr cur) {
 	int secres;
 
 	secres = xsltCheckRead(sec, NULL, URI);
-	if (secres == 0) {
-	    xsltTransformError(NULL, NULL, NULL,
-		 "xsl:import: read rights for %s denied\n",
-			     URI);
+	if (secres <= 0) {
+            if (secres == 0)
+                xsltTransformError(NULL, NULL, NULL,
+                     "xsl:import: read rights for %s denied\n",
+                                 URI);
 	    goto error;
 	}
     }

libxslt/transform.c

@@ -3493,10 +3493,11 @@ xsltDocumentElem(xsltTransformContextPtr ctxt, xmlNodePtr node,
      */
     if (ctxt->sec != NULL) {
 	ret = xsltCheckWrite(ctxt->sec, ctxt, filename);
-	if (ret == 0) {
-	    xsltTransformError(ctxt, NULL, inst,
-		 "xsltDocumentElem: write rights for %s denied\n",
-			     filename);
+	if (ret <= 0) {
+            if (ret == 0)
+                xsltTransformError(ctxt, NULL, inst,
+                     "xsltDocumentElem: write rights for %s denied\n",
+                                 filename);
 	    xmlFree(URL);
 	    xmlFree(filename);
 	    return;

libxslt/xslt.c

@@ -6763,10 +6763,11 @@ xsltParseStylesheetFile(const xmlChar* filename) {
 	int res;
 
 	res = xsltCheckRead(sec, NULL, filename);
-	if (res == 0) {
-	    xsltTransformError(NULL, NULL, NULL,
-		 "xsltParseStylesheetFile: read rights for %s denied\n",
-			     filename);
+	if (res <= 0) {
+            if (res == 0)
+                xsltTransformError(NULL, NULL, NULL,
+                     "xsltParseStylesheetFile: read rights for %s denied\n",
+                                 filename);
 	    return(NULL);
 	}
     }

[Joseph Konczal]

It is good that errors are now treated as permission denied. It seems strange, however, that there is no error message created to let somebody find out what happened.

[Nick Wellnhofer]

@jkonczal In libxslt, if a function returns an error code, it means that an error has already been reported. Here's an example: https://gitlab.gnome.org/GNOME/libxslt/blob/master/libxslt/security.c#L443

[Joseph Konczal]

That explains it. Thanks.

[Tomasz Kłoczko]

Is it any change to make new release with that fix?