[libxslt] Fix security framework bypass

[Nick Wellnhofer <nwellnhof src gnome org>]

commit e03553605b45c88f0b4b2980adfbbb8f6fca2fd6
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sun Mar 24 09:51:39 2019 +0100

    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 | 18 ++++++++++--------
 libxslt/imports.c   |  9 +++++----
 libxslt/transform.c |  9 +++++----
 libxslt/xslt.c      |  9 +++++----
 4 files changed, 25 insertions(+), 20 deletions(-)
---
diff --git a/libxslt/documents.c b/libxslt/documents.c
index 3f3a7312..4aad11bb 100644
--- a/libxslt/documents.c
+++ b/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);
        }
     }
diff --git a/libxslt/imports.c b/libxslt/imports.c
index 874870cc..3783b247 100644
--- a/libxslt/imports.c
+++ b/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;
        }
     }
diff --git a/libxslt/transform.c b/libxslt/transform.c
index 13793914..0636dbd0 100644
--- a/libxslt/transform.c
+++ b/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;
diff --git a/libxslt/xslt.c b/libxslt/xslt.c
index 780a5ad7..a234eb79 100644
--- a/libxslt/xslt.c
+++ b/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);
        }
     }