Fixes Issue #19081: When a zipimport .zip file in sys.path being imported from

is modified during the lifetime of the Python process after zipimport has
already cached the zip's table of contents we detect this and recover
rather than read bad data from the .zip (causing odd import errors).

1 files changed, 238 insertions, 47 deletions

diff --git a/Modules/zipimport.c b/Modules/zipimport.c
index 2feb2a8..bfac462 100644
--- a/Modules/zipimport.c
+++ b/Modules/zipimport.c
@@ -45,10 +45,16 @@ struct _zipimporter {
 static PyObject *ZipImportError;
 /* read_directory() cache */
 static PyObject *zip_directory_cache = NULL;
+static PyObject *zip_stat_cache = NULL;
+/* posix.fstat or nt.fstat function.  Used due to posixmodule.c's
+ * superior fstat implementation over libc's on Windows. */
+static PyObject *fstat_function = NULL;  /* posix.fstat() or nt.fstat() */
 
 /* forward decls */
-static PyObject *read_directory(PyObject *archive);
-static PyObject *get_data(PyObject *archive, PyObject *toc_entry);
+static FILE *fopen_rb_and_stat(PyObject *path, PyObject **py_stat_p);
+static FILE *safely_reopen_archive(ZipImporter *self);
+static PyObject *read_directory(FILE *fp, PyObject *archive);
+static PyObject *get_data(FILE *fp, PyObject *archive, PyObject *toc_entry);
 static PyObject *get_module_code(ZipImporter *self, PyObject *fullname,
                                  int *p_ispackage, PyObject **p_modpath);
 
@@ -128,11 +134,39 @@ zipimporter_init(ZipImporter *self, PyObject *args, PyObject *kwds)
 
     files = PyDict_GetItem(zip_directory_cache, filename);
     if (files == NULL) {
-        files = read_directory(filename);
-        if (files == NULL)
+        PyObject *zip_stat = NULL;
+        FILE *fp = fopen_rb_and_stat(filename, &zip_stat);
+        if (fp == NULL) {
+            if (!PyErr_Occurred())
+                PyErr_Format(ZipImportError, "can't open Zip file: %R",
+                             filename);
+
+            Py_XDECREF(zip_stat);
             goto error;
-        if (PyDict_SetItem(zip_directory_cache, filename, files) != 0)
+        }
+
+        if (Py_VerboseFlag)
+            PySys_FormatStderr("# zipimport: %U not cached, "
+                               "reading TOC.\n", filename);
+
+        files = read_directory(fp, filename);
+        fclose(fp);
+        if (files == NULL) {
+            Py_XDECREF(zip_stat);
+            goto error;
+        }
+        if (PyDict_SetItem(zip_directory_cache, filename, files) != 0) {
+            Py_DECREF(files);
+            Py_XDECREF(zip_stat);
             goto error;
+        }
+        if (zip_stat && PyDict_SetItem(zip_stat_cache, filename,
+                                       zip_stat) != 0) {
+            Py_DECREF(files);
+            Py_DECREF(zip_stat);
+            goto error;
+        }
+        Py_XDECREF(zip_stat);
     }
     else
         Py_INCREF(files);
@@ -554,10 +588,11 @@ zipimporter_get_data(PyObject *obj, PyObject *args)
 {
     ZipImporter *self = (ZipImporter *)obj;
     PyObject *path, *key;
+    FILE *fp;
 #ifdef ALTSEP
     _Py_IDENTIFIER(replace);
 #endif
-    PyObject *toc_entry;
+    PyObject *toc_entry, *data;
     Py_ssize_t path_start, path_len, len;
 
     if (!PyArg_ParseTuple(args, "U:zipimporter.get_data", &path))
@@ -585,15 +620,23 @@ zipimporter_get_data(PyObject *obj, PyObject *args)
     key = PyUnicode_Substring(path, path_start, path_len);
     if (key == NULL)
         goto error;
+
+    fp = safely_reopen_archive(self);
+    if (fp == NULL)
+        goto error;
+
     toc_entry = PyDict_GetItem(self->files, key);
     if (toc_entry == NULL) {
         PyErr_SetFromErrnoWithFilenameObject(PyExc_IOError, key);
         Py_DECREF(key);
+        fclose(fp);
         goto error;
     }
     Py_DECREF(key);
     Py_DECREF(path);
-    return get_data(self->archive, toc_entry);
+    data = get_data(fp, self->archive, toc_entry);
+    fclose(fp);
+    return data;
   error:
     Py_DECREF(path);
     return NULL;
@@ -618,6 +661,7 @@ zipimporter_get_source(PyObject *obj, PyObject *args)
     PyObject *toc_entry;
     PyObject *fullname, *subname, *path, *fullpath;
     enum zi_module_info mi;
+    FILE *fp;
 
     if (!PyArg_ParseTuple(args, "U:zipimporter.get_source", &fullname))
         return NULL;
@@ -647,11 +691,18 @@ zipimporter_get_source(PyObject *obj, PyObject *args)
     if (fullpath == NULL)
         return NULL;
 
+    fp = safely_reopen_archive(self);
+    if (fp == NULL) {
+        Py_DECREF(fullpath);
+        return NULL;
+    }
+
     toc_entry = PyDict_GetItem(self->files, fullpath);
     Py_DECREF(fullpath);
     if (toc_entry != NULL) {
         PyObject *res, *bytes;
-        bytes = get_data(self->archive, toc_entry);
+        bytes = get_data(fp, self->archive, toc_entry);
+        fclose(fp);
         if (bytes == NULL)
             return NULL;
         res = PyUnicode_FromStringAndSize(PyBytes_AS_STRING(bytes),
@@ -659,10 +710,10 @@ zipimporter_get_source(PyObject *obj, PyObject *args)
         Py_DECREF(bytes);
         return res;
     }
+    fclose(fp);
 
     /* we have the module, but no source */
-    Py_INCREF(Py_None);
-    return Py_None;
+    Py_RETURN_NONE;
 }
 
 PyDoc_STRVAR(doc_find_module,
@@ -828,10 +879,135 @@ get_long(unsigned char *buf) {
     return x;
 }
 
+/* Return 1 if objects a and b fail a Py_EQ test for an attr. */
+static int
+compare_obj_attr_strings(PyObject *obj_a, PyObject *obj_b, char *attr_name)
+{
+    int problem = 0;
+    PyObject *attr_a = PyObject_GetAttrString(obj_a, attr_name);
+    PyObject *attr_b = PyObject_GetAttrString(obj_b, attr_name);
+    if (attr_a == NULL || attr_b == NULL)
+        problem = 1;
+    else
+        problem = (PyObject_RichCompareBool(attr_a, attr_b, Py_EQ) != 1);
+    Py_XDECREF(attr_a);
+    Py_XDECREF(attr_b);
+    return problem;
+}
+
+/*
+ * Returns an open FILE * on success.
+ * Returns NULL on error with the Python error context set.
+ */
+static FILE *
+safely_reopen_archive(ZipImporter *self)
+{
+    FILE *fp;
+    PyObject *stat_now = NULL;
+
+    fp = fopen_rb_and_stat(self->archive, &stat_now);
+    if (!fp) {
+        PyErr_Format(ZipImportError,
+                     "zipimport: can not open file %U", self->archive);
+        Py_XDECREF(stat_now);
+        return NULL;
+    }
+
+    if (stat_now != NULL) {
+        int problem = 0;
+        PyObject *files;
+        PyObject *prev_stat = PyDict_GetItem(zip_stat_cache, self->archive);
+        /* Test stat_now vs the old cached stat on some key attributes. */
+        if (prev_stat != NULL) {
+            problem = compare_obj_attr_strings(prev_stat, stat_now,
+                                               "st_ino");
+            problem |= compare_obj_attr_strings(prev_stat, stat_now,
+                                                "st_size");
+            problem |= compare_obj_attr_strings(prev_stat, stat_now,
+                                                "st_mtime");
+        } else {
+            if (Py_VerboseFlag)
+                PySys_FormatStderr("# zipimport: no stat data for %U!\n",
+                                   self->archive);
+            problem = 1;
+        }
+
+        if (problem) {
+            if (Py_VerboseFlag)
+                PySys_FormatStderr("# zipimport: %U modified since last"
+                                   " import, rereading TOC.\n", self->archive);
+            files = read_directory(fp, self->archive);
+            if (files == NULL) {
+                Py_DECREF(stat_now);
+                fclose(fp);
+                return NULL;
+            }
+            if (PyDict_SetItem(zip_directory_cache, self->archive,
+                               files) != 0) {
+                Py_DECREF(files);
+                Py_DECREF(stat_now);
+                fclose(fp);
+                return NULL;
+            }
+            if (stat_now && PyDict_SetItem(zip_stat_cache, self->archive,
+                                           stat_now) != 0) {
+                Py_DECREF(files);
+                Py_DECREF(stat_now);
+                fclose(fp);
+                return NULL;
+            }
+            Py_XDECREF(self->files);  /* free the old value. */
+            self->files = files;
+        } else {
+            /* No problem, discard the new stat data. */
+            Py_DECREF(stat_now);
+        }
+    }  /* stat succeeded */
+
+    return fp;
+}
+
+/*
+   fopen_rb_and_stat(path, &py_stat) -> FILE *
+
+   Opens path in "rb" mode and populates the Python py_stat stat_result
+   with information about the opened file.  *py_stat may not be changed
+   if there is no fstat_function or if fstat_function fails.
+
+   Returns NULL and does nothing to *py_stat if the open failed.
+*/
+static FILE *
+fopen_rb_and_stat(PyObject *path, PyObject **py_stat_p)
+{
+    FILE *fp;
+    assert(py_stat_p != NULL);
+    assert(*py_stat_p == NULL);
+
+    fp = _Py_fopen(path, "rb");
+    if (fp == NULL) {
+        if (!PyErr_Occurred())
+            PyErr_Format(ZipImportError,
+                         "zipimport: can not open file %U", path);
+        return NULL;
+    }
+
+    if (fstat_function) {
+        PyObject *stat_result = PyObject_CallFunction(fstat_function,
+                                                      "i", fileno(fp));
+        if (stat_result == NULL) {
+            PyErr_Clear();  /* We can function without it. */
+        } else {
+            *py_stat_p = stat_result;
+        }
+    }
+
+    return fp;
+}
+
 /*
-   read_directory(archive) -> files dict (new reference)
+   read_directory(fp, archive) -> files dict (new reference)
 
-   Given a path to a Zip archive, build a dict, mapping file names
+   Given an open Zip archive, build a dict, mapping file names
    (local to the archive, using SEP as a separator) to toc entries.
 
    A toc_entry is a tuple:
@@ -851,10 +1027,9 @@ get_long(unsigned char *buf) {
    data_size and file_offset are 0.
 */
 static PyObject *
-read_directory(PyObject *archive)
+read_directory(FILE *fp, PyObject *archive)
 {
     PyObject *files = NULL;
-    FILE *fp;
     unsigned short flags;
     short compress, time, date, name_size;
     long crc, data_size, file_size, header_size;
@@ -869,27 +1044,18 @@ read_directory(PyObject *archive)
     const char *charset;
     int bootstrap;
 
-    fp = _Py_fopen(archive, "rb");
-    if (fp == NULL) {
-        if (!PyErr_Occurred())
-            PyErr_Format(ZipImportError, "can't open Zip file: %R", archive);
-        return NULL;
-    }
-
+    assert(fp != NULL);
     if (fseek(fp, -22, SEEK_END) == -1) {
-        fclose(fp);
         PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
         return NULL;
     }
     header_position = ftell(fp);
     if (fread(endof_central_dir, 1, 22, fp) != 22) {
-        fclose(fp);
         PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
         return NULL;
     }
     if (get_long((unsigned char *)endof_central_dir) != 0x06054B50) {
         /* Bad: End of Central Dir signature */
-        fclose(fp);
         PyErr_Format(ZipImportError, "not a Zip file: %R", archive);
         return NULL;
     }
@@ -983,19 +1149,16 @@ read_directory(PyObject *archive)
             goto error;
         count++;
     }
-    fclose(fp);
     if (Py_VerboseFlag)
         PySys_FormatStderr("# zipimport: found %ld names in %R\n",
                            count, archive);
     return files;
 fseek_error:
-    fclose(fp);
     Py_XDECREF(files);
     Py_XDECREF(nameobj);
     PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
     return NULL;
 error:
-    fclose(fp);
     Py_XDECREF(files);
     Py_XDECREF(nameobj);
     return NULL;
@@ -1034,14 +1197,13 @@ get_decompress_func(void)
     return decompress;
 }
 
-/* Given a path to a Zip file and a toc_entry, return the (uncompressed)
+/* Given a FILE* to a Zip file and a toc_entry, return the (uncompressed)
    data as a new reference. */
 static PyObject *
-get_data(PyObject *archive, PyObject *toc_entry)
+get_data(FILE *fp, PyObject *archive, PyObject *toc_entry)
 {
     PyObject *raw_data, *data = NULL, *decompress;
     char *buf;
-    FILE *fp;
     int err;
     Py_ssize_t bytes_read = 0;
     long l;
@@ -1055,17 +1217,8 @@ get_data(PyObject *archive, PyObject *toc_entry)
         return NULL;
     }
 
-    fp = _Py_fopen(archive, "rb");
-    if (!fp) {
-        if (!PyErr_Occurred())
-            PyErr_Format(PyExc_IOError,
-               "zipimport: can not open file %U", archive);
-        return NULL;
-    }
-
     /* Check to make sure the local file header is correct */
     if (fseek(fp, file_offset, 0) == -1) {
-        fclose(fp);
         PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
         return NULL;
     }
@@ -1076,11 +1229,9 @@ get_data(PyObject *archive, PyObject *toc_entry)
         PyErr_Format(ZipImportError,
                      "bad local file header in %U",
                      archive);
-        fclose(fp);
         return NULL;
     }
     if (fseek(fp, file_offset + 26, 0) == -1) {
-        fclose(fp);
         PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
         return NULL;
     }
@@ -1095,7 +1246,6 @@ get_data(PyObject *archive, PyObject *toc_entry)
     raw_data = PyBytes_FromStringAndSize((char *)NULL, bytes_size);
 
     if (raw_data == NULL) {
-        fclose(fp);
         return NULL;
     }
     buf = PyBytes_AsString(raw_data);
@@ -1104,11 +1254,9 @@ get_data(PyObject *archive, PyObject *toc_entry)
     if (err == 0) {
         bytes_read = fread(buf, 1, data_size, fp);
     } else {
-        fclose(fp);
         PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
         return NULL;
     }
-    fclose(fp);
     if (err || bytes_read != data_size) {
         PyErr_SetString(PyExc_IOError,
                         "zipimport: can't read data");
@@ -1329,12 +1477,12 @@ get_mtime_of_source(ZipImporter *self, PyObject *path)
 /* Return the code object for the module named by 'fullname' from the
    Zip archive as a new reference. */
 static PyObject *
-get_code_from_data(ZipImporter *self, int ispackage, int isbytecode,
+get_code_from_data(ZipImporter *self, FILE *fp, int ispackage, int isbytecode,
                    time_t mtime, PyObject *toc_entry)
 {
     PyObject *data, *modpath, *code;
 
-    data = get_data(self->archive, toc_entry);
+    data = get_data(fp, self->archive, toc_entry);
     if (data == NULL)
         return NULL;
 
@@ -1356,6 +1504,7 @@ get_module_code(ZipImporter *self, PyObject *fullname,
     PyObject *code = NULL, *toc_entry, *subname;
     PyObject *path, *fullpath = NULL;
     struct st_zip_searchorder *zso;
+    FILE *fp;
 
     subname = get_subname(fullname);
     if (subname == NULL)
@@ -1366,6 +1515,12 @@ get_module_code(ZipImporter *self, PyObject *fullname,
     if (path == NULL)
         return NULL;
 
+    fp = safely_reopen_archive(self);
+    if (fp == NULL) {
+        Py_DECREF(path);
+        return NULL;
+    }
+
     for (zso = zip_searchorder; *zso->suffix; zso++) {
         code = NULL;
 
@@ -1376,6 +1531,7 @@ get_module_code(ZipImporter *self, PyObject *fullname,
         if (Py_VerboseFlag > 1)
             PySys_FormatStderr("# trying %U%c%U\n",
                                self->archive, (int)SEP, fullpath);
+
         toc_entry = PyDict_GetItem(self->files, fullpath);
         if (toc_entry != NULL) {
             time_t mtime = 0;
@@ -1391,7 +1547,7 @@ get_module_code(ZipImporter *self, PyObject *fullname,
             Py_CLEAR(fullpath);
             if (p_ispackage != NULL)
                 *p_ispackage = ispackage;
-            code = get_code_from_data(self, ispackage,
+            code = get_code_from_data(self, fp, ispackage,
                                       isbytecode, mtime,
                                       toc_entry);
             if (code == Py_None) {
@@ -1411,6 +1567,7 @@ get_module_code(ZipImporter *self, PyObject *fullname,
     }
     PyErr_Format(ZipImportError, "can't find module %R", fullname);
 exit:
+    fclose(fp);
     Py_DECREF(path);
     Py_XDECREF(fullpath);
     return code;
@@ -1428,6 +1585,8 @@ This module exports three objects:\n\
   subclass of ImportError, so it can be caught as ImportError, too.\n\
 - _zip_directory_cache: a dict, mapping archive paths to zip directory\n\
   info dicts, as used in zipimporter._files.\n\
+- _zip_stat_cache: a dict, mapping archive paths to stat_result\n\
+  info for the .zip the last time anything was imported from it.\n\
 \n\
 It is usually not needed to use the zipimport module explicitly; it is\n\
 used by the builtin import mechanism for sys.path items that are paths\n\
@@ -1487,6 +1646,7 @@ PyInit_zipimport(void)
                            (PyObject *)&ZipImporter_Type) < 0)
         return NULL;
 
+    Py_XDECREF(zip_directory_cache);  /* Avoid embedded interpreter leaks. */
     zip_directory_cache = PyDict_New();
     if (zip_directory_cache == NULL)
         return NULL;
@@ -1494,5 +1654,36 @@ PyInit_zipimport(void)
     if (PyModule_AddObject(mod, "_zip_directory_cache",
                            zip_directory_cache) < 0)
         return NULL;
+
+    Py_XDECREF(zip_stat_cache);  /* Avoid embedded interpreter leaks. */
+    zip_stat_cache = PyDict_New();
+    if (zip_stat_cache == NULL)
+        return NULL;
+    Py_INCREF(zip_stat_cache);
+    if (PyModule_AddObject(mod, "_zip_stat_cache", zip_stat_cache) < 0)
+        return NULL;
+
+    {
+        /* We cannot import "os" here as that is a .py/.pyc file that could
+         * live within a zipped up standard library.  Import the posix or nt
+         * builtin that provides the fstat() function we want instead. */
+        PyObject *os_like_module;
+        Py_CLEAR(fstat_function);  /* Avoid embedded interpreter leaks. */
+        os_like_module = PyImport_ImportModule("posix");
+        if (os_like_module == NULL) {
+            PyErr_Clear();
+            os_like_module = PyImport_ImportModule("nt");
+        }
+        if (os_like_module != NULL) {
+            fstat_function = PyObject_GetAttrString(os_like_module, "fstat");
+            Py_DECREF(os_like_module);
+        }
+        if (fstat_function == NULL) {
+            PyErr_Clear();  /* non-fatal, we'll go on without it. */
+            if (Py_VerboseFlag)
+                PySys_WriteStderr("# zipimport unable to use os.fstat().\n");
+        }
+    }
+
     return mod;
 }