[xml] Race condition in xsltInit (thread safety)

["Christopher R. Palmer" <crpalmer vivisimo com>]

Hi,

I am using 1.1.15 of libxslt with multiple threads and I am seeing 
occasional crashes in the (libc) free function.  The stack traces look 
something like:

xsltParseStylesheetDoc
...
xsltNewStylesheet
xslInit
xsltRegisterAllExtras
xsltRegisterExtModuleFunction
...
xmlHashUpdateEntry3
...
[free]

Digging into this a little more, it looks like xsltInit is called every 
time that a new stylesheet is parsed.  xsltInit uses xsltRegisterAllExtras 
which always updates all of the hash entries and the hash function is (not 
surprisingly) not thread safe for updates.

CVS tells me that xsltInit was changed to fix bug #165201 (calling xsltInit 
multiple times) where previously it had a local static initialized flag.

The best fix I can suggest is to export xsltInit and have a static 
initialized flag.  To not break the fix of bug #165201, add an internal 
function to signal that the library is no longer initialized.

I've attached such a patch for possible inclusion in the code base.

Cheers,
Chris.

diff -r --unified orig/libxslt-1.1.15/libxslt/extensions.c libxslt-1.1.15/libxslt/extensions.c
Index: orig/libxslt-1.1.15/libxslt/extensions.c
--- orig/libxslt-1.1.15/libxslt/extensions.c    2005-01-15 18:00:52.000000000 -0500
+++ libxslt-1.1.15/libxslt/extensions.c 2006-02-20 12:42:52.000000000 -0500
@@ -1881,6 +1881,8 @@
         xmlHashFree(xsltModuleHash, NULL);
         xsltModuleHash = NULL;
     }
+
+    xsltUninit();
 }
 
 static void
diff -r --unified orig/libxslt-1.1.15/libxslt/xslt.c libxslt-1.1.15/libxslt/xslt.c
Index: orig/libxslt-1.1.15/libxslt/xslt.c
--- orig/libxslt-1.1.15/libxslt/xslt.c  2005-08-25 07:28:07.000000000 -0400
+++ libxslt-1.1.15/libxslt/xslt.c       2006-02-20 12:43:53.000000000 -0500
@@ -148,9 +148,26 @@
  * Initializes the processor (e.g. registers built-in extensions,
  * etc.)
  */
-static void
+
+static int initialized = 0;
+
+void
 xsltInit (void) {
-    xsltRegisterAllExtras();
+    if (initialized == 0) {
+       initialized = 1;
+        xsltRegisterAllExtras();
+    }
+}
+
+/**
+ * xsltUninit
+ *
+ * Uninitializes the processor.
+ */
+
+void
+xsltUninit (void) {
+    initialized = 0;
 }
 
 /**
diff -r --unified orig/libxslt-1.1.15/libxslt/xslt.h libxslt-1.1.15/libxslt/xslt.h
Index: orig/libxslt-1.1.15/libxslt/xslt.h
--- orig/libxslt-1.1.15/libxslt/xslt.h  2004-08-19 02:49:42.000000000 -0400
+++ libxslt-1.1.15/libxslt/xslt.h       2006-02-20 12:45:38.000000000 -0500
@@ -83,6 +83,13 @@
 XSLTPUBVAR const int xsltLibxmlVersion;
 
 /*
+ * Global initialization function.
+ */
+
+XSLTPUBFUN void XSLTCALL
+               xsltInit                (void);
+
+/*
  * Global cleanup function.
  */
 XSLTPUBFUN void XSLTCALL       
diff -r --unified orig/libxslt-1.1.15/libxslt/xsltInternals.h libxslt-1.1.15/libxslt/xsltInternals.h
--- orig/libxslt-1.1.15/libxslt/xsltInternals.h 2005-03-29 05:40:26.000000000 -0500
+++ libxslt-1.1.15/libxslt/xsltInternals.h      2006-02-20 12:47:35.000000000 -0500
@@ -694,6 +694,14 @@
                                                 xmlNodePtr node);
 XSLTPUBFUN void XSLTCALL
                        xsltFreeAVTList         (void *avt);
+
+/*
+ * Extra function for successful xsltCleanupGlobals / xsltInit sequence.
+ */
+
+XSLTPUBFUN void XSLTCALL
+                       xsltUninit              (void);
+
 #ifdef __cplusplus
 }
 #endif