Detect conflicting Python DLL on module import under Windows - as per [ Patch #101676 ]

Author: mhammond

Python/dynload_win.c

@@ -3,6 +3,7 @@
 
 #include <windows.h>
 #include <direct.h>
+#include <ctype.h>
 
 #include "Python.h"
 #include "importdl.h"
@@ -19,11 +20,144 @@ const struct filedescr _PyImport_DynLoadFiletab[] = {
 };
 
 
+#ifdef MS_WIN32
+
+/* Case insensitive string compare, to avoid any dependencies on particular
+   C RTL implementations */
+
+static int strcasecmp (char *string1, char *string2)
+{ 
+	int first, second;
+
+	do {
+		first  = tolower(*string1);
+		second = tolower(*string2);
+		string1++;
+		string2++;
+	} while (first && first == second);
+
+	return (first - second);
+} 
+
+
+/* Function to return the name of the "python" DLL that the supplied module
+   directly imports.  Looks through the list of imported modules and
+   returns the first entry that starts with "python" (case sensitive) and
+   is followed by nothing but numbers until the separator (period).
+
+   Returns a pointer to the import name, or NULL if no matching name was
+   located.
+
+   This function parses through the PE header for the module as loaded in
+   memory by the system loader.  The PE header is accessed as documented by
+   Microsoft in the MSDN PE and COFF specification (2/99), and handles
+   both PE32 and PE32+.  It only worries about the direct import table and
+   not the delay load import table since it's unlikely an extension is
+   going to be delay loading Python (after all, it's already loaded).
+
+   If any magic values are not found (e.g., the PE header or optional
+   header magic), then this function simply returns NULL. */
+
+#define DWORD_AT(mem) (*(DWORD *)(mem))
+#define WORD_AT(mem)  (*(WORD *)(mem))
+
+static char *GetPythonImport (HINSTANCE hModule)
+{
+	unsigned char *dllbase, *import_data, *import_name;
+	DWORD pe_offset, opt_offset;
+	WORD opt_magic;
+	int num_dict_off, import_off;
+
+	/* Safety check input */
+	if (hModule == NULL) {
+		return NULL;
+	}
+
+	/* Module instance is also the base load address.  First portion of
+	   memory is the MS-DOS loader, which holds the offset to the PE
+	   header (from the load base) at 0x3C */
+	dllbase = (unsigned char *)hModule;
+	pe_offset = DWORD_AT(dllbase + 0x3C);
+
+	/* The PE signature must be "PE\0\0" */
+	if (memcmp(dllbase+pe_offset,"PE\0\0",4)) {
+		return NULL;
+	}
+
+	/* Following the PE signature is the standard COFF header (20
+	   bytes) and then the optional header.  The optional header starts
+	   with a magic value of 0x10B for PE32 or 0x20B for PE32+ (PE32+
+	   uses 64-bits for some fields).  It might also be 0x107 for a ROM
+	   image, but we don't process that here.
+
+	   The optional header ends with a data dictionary that directly
+	   points to certain types of data, among them the import entries
+	   (in the second table entry). Based on the header type, we
+	   determine offsets for the data dictionary count and the entry
+	   within the dictionary pointing to the imports. */
+
+	opt_offset = pe_offset + 4 + 20;
+	opt_magic = WORD_AT(dllbase+opt_offset);
+	if (opt_magic == 0x10B) {
+		/* PE32 */
+		num_dict_off = 92;
+		import_off   = 104;
+	} else if (opt_magic == 0x20B) {
+		/* PE32+ */
+		num_dict_off = 108;
+		import_off   = 120;
+	} else {
+		/* Unsupported */
+		return NULL;
+	}
+
+	/* Now if an import table exists, offset to it and walk the list of
+	   imports.  The import table is an array (ending when an entry has
+	   empty values) of structures (20 bytes each), which contains (at
+	   offset 12) a relative address (to the module base) at which a
+	   string constant holding the import name is located. */
+
+	if (DWORD_AT(dllbase + opt_offset + num_dict_off) >= 2) {
+		import_data = dllbase + DWORD_AT(dllbase +
+						 opt_offset +
+						 import_off);
+		while (DWORD_AT(import_data)) {
+			import_name = dllbase + DWORD_AT(import_data+12);
+			if (strlen(import_name) >= 6 &&
+			    !strncmp(import_name,"python",6)) {
+				char *pch;
+
+				/* Ensure python prefix is followed only
+				   by numbers to the end of the basename */
+				pch = import_name + 6;
+				while (*pch && *pch != '.') {
+					if (*pch >= '0' && *pch <= '9') {
+						pch++;
+					} else {
+						pch = NULL;
+						break;
+					}
+				}
+	    
+				if (pch) {
+					/* Found it - return the name */
+					return import_name;
+				}
+			}
+			import_data += 20;
+		}
+	}
+
+	return NULL;
+}
+#endif /* MS_WIN32 */
+
+
 dl_funcptr _PyImport_GetDynLoadFunc(const char *fqname, const char *shortname,
 				    const char *pathname, FILE *fp)
 {
 	dl_funcptr p;
-	char funcname[258];
+	char funcname[258], *import_python;
 
 	sprintf(funcname, "init%.200s", shortname);
 
@@ -91,6 +225,23 @@ dl_funcptr _PyImport_GetDynLoadFunc(const char *fqname, const char *shortname,
 			}
 			PyErr_SetString(PyExc_ImportError, errBuf);
 		return NULL;
+		} else {
+			char buffer[256];
+
+			sprintf(buffer,"python%d%d.dll",
+				PY_MAJOR_VERSION,PY_MINOR_VERSION);
+			import_python = GetPythonImport(hDLL);
+
+			if (import_python &&
+			    strcasecmp(buffer,import_python)) {
+				sprintf(buffer,
+					"Module use of %s conflicts "
+					"with this version of Python.",
+					import_python);
+				PyErr_SetString(PyExc_ImportError,buffer);
+				FreeLibrary(hDLL);
+				return NULL;
+			}
 		}
 		p = GetProcAddress(hDLL, funcname);
 	}