gh-109613: _pystat_fromstructstat() checks for exceptions (#109618)

Fix os.stat() and os.DirEntry.stat(): check for exceptions.
Previously, on Python built in debug mode, these functions could
trigger a fatal Python error (and abort the process) when a function
succeeded with an exception set.

_pystat_fromstructstat() now exits immediately if an exception is
raised, rather only checking for exceptions at the end. It fix
following fatal error in fill_time():

    Fatal Python error: _Py_CheckSlotResult:
    Slot * of type int succeeded with an exception set

Author: vstinner

Misc/NEWS.d/next/Library/2023-09-20-17-45-46.gh-issue-109613.P13ogN.rst

@@ -0,0 +1,4 @@
+Fix :func:`os.stat` and :meth:`os.DirEntry.stat`: check for exceptions.
+Previously, on Python built in debug mode, these functions could trigger a
+fatal Python error (and abort the process) when a function succeeded with an
+exception set. Patch by Victor Stinner.

Modules/posixmodule.c

@@ -2396,21 +2396,26 @@ _posix_free(void *module)
    _posix_clear((PyObject *)module);
 }
 
-static void
+static int
 fill_time(PyObject *module, PyObject *v, int s_index, int f_index, int ns_index, time_t sec, unsigned long nsec)
 {
-    PyObject *s = _PyLong_FromTime_t(sec);
-    PyObject *ns_fractional = PyLong_FromUnsignedLong(nsec);
+    assert(!PyErr_Occurred());
+
+    int res = -1;
     PyObject *s_in_ns = NULL;
     PyObject *ns_total = NULL;
     PyObject *float_s = NULL;
 
-    if (!(s && ns_fractional))
+    PyObject *s = _PyLong_FromTime_t(sec);
+    PyObject *ns_fractional = PyLong_FromUnsignedLong(nsec);
+    if (!(s && ns_fractional)) {
         goto exit;
+    }
 
     s_in_ns = PyNumber_Multiply(s, get_posix_state(module)->billion);
-    if (!s_in_ns)
+    if (!s_in_ns) {
         goto exit;
+    }
 
     ns_total = PyNumber_Add(s_in_ns, ns_fractional);
     if (!ns_total)
@@ -2433,12 +2438,17 @@ fill_time(PyObject *module, PyObject *v, int s_index, int f_index, int ns_index,
         PyStructSequence_SET_ITEM(v, ns_index, ns_total);
         ns_total = NULL;
     }
+
+    assert(!PyErr_Occurred());
+    res = 0;
+
 exit:
     Py_XDECREF(s);
     Py_XDECREF(ns_fractional);
     Py_XDECREF(s_in_ns);
     Py_XDECREF(ns_total);
     Py_XDECREF(float_s);
+    return res;
 }
 
 #ifdef MS_WINDOWS
@@ -2473,34 +2483,47 @@ _pystat_l128_from_l64_l64(uint64_t low, uint64_t high)
 static PyObject*
 _pystat_fromstructstat(PyObject *module, STRUCT_STAT *st)
 {
-    unsigned long ansec, mnsec, cnsec;
+    assert(!PyErr_Occurred());
+
     PyObject *StatResultType = get_posix_state(module)->StatResultType;
     PyObject *v = PyStructSequence_New((PyTypeObject *)StatResultType);
-    if (v == NULL)
+    if (v == NULL) {
         return NULL;
+    }
+
+#define SET_ITEM(pos, expr) \
+    do { \
+        PyObject *obj = (expr); \
+        if (obj == NULL) { \
+            goto error; \
+        } \
+        PyStructSequence_SET_ITEM(v, (pos), obj); \
+    } while (0)
 
-    PyStructSequence_SET_ITEM(v, 0, PyLong_FromLong((long)st->st_mode));
+    SET_ITEM(0, PyLong_FromLong((long)st->st_mode));
 #ifdef MS_WINDOWS
-    PyStructSequence_SET_ITEM(v, 1, _pystat_l128_from_l64_l64(st->st_ino, st->st_ino_high));
-    PyStructSequence_SET_ITEM(v, 2, PyLong_FromUnsignedLongLong(st->st_dev));
+    SET_ITEM(1, _pystat_l128_from_l64_l64(st->st_ino, st->st_ino_high));
+    SET_ITEM(2, PyLong_FromUnsignedLongLong(st->st_dev));
 #else
     static_assert(sizeof(unsigned long long) >= sizeof(st->st_ino),
                   "stat.st_ino is larger than unsigned long long");
-    PyStructSequence_SET_ITEM(v, 1, PyLong_FromUnsignedLongLong(st->st_ino));
-    PyStructSequence_SET_ITEM(v, 2, _PyLong_FromDev(st->st_dev));
+    SET_ITEM(1, PyLong_FromUnsignedLongLong(st->st_ino));
+    SET_ITEM(2, _PyLong_FromDev(st->st_dev));
 #endif
-    PyStructSequence_SET_ITEM(v, 3, PyLong_FromLong((long)st->st_nlink));
+    SET_ITEM(3, PyLong_FromLong((long)st->st_nlink));
 #if defined(MS_WINDOWS)
-    PyStructSequence_SET_ITEM(v, 4, PyLong_FromLong(0));
-    PyStructSequence_SET_ITEM(v, 5, PyLong_FromLong(0));
+    SET_ITEM(4, PyLong_FromLong(0));
+    SET_ITEM(5, PyLong_FromLong(0));
 #else
-    PyStructSequence_SET_ITEM(v, 4, _PyLong_FromUid(st->st_uid));
-    PyStructSequence_SET_ITEM(v, 5, _PyLong_FromGid(st->st_gid));
+    SET_ITEM(4, _PyLong_FromUid(st->st_uid));
+    SET_ITEM(5, _PyLong_FromGid(st->st_gid));
 #endif
     static_assert(sizeof(long long) >= sizeof(st->st_size),
                   "stat.st_size is larger than long long");
-    PyStructSequence_SET_ITEM(v, 6, PyLong_FromLongLong(st->st_size));
+    SET_ITEM(6, PyLong_FromLongLong(st->st_size));
 
+    // Set st_atime, st_mtime and st_ctime
+    unsigned long ansec, mnsec, cnsec;
 #if defined(HAVE_STAT_TV_NSEC)
     ansec = st->st_atim.tv_nsec;
     mnsec = st->st_mtim.tv_nsec;
@@ -2516,67 +2539,67 @@ _pystat_fromstructstat(PyObject *module, STRUCT_STAT *st)
 #else
     ansec = mnsec = cnsec = 0;
 #endif
-    fill_time(module, v, 7, 10, 13, st->st_atime, ansec);
-    fill_time(module, v, 8, 11, 14, st->st_mtime, mnsec);
-    fill_time(module, v, 9, 12, 15, st->st_ctime, cnsec);
+    if (fill_time(module, v, 7, 10, 13, st->st_atime, ansec) < 0) {
+        goto error;
+    }
+    if (fill_time(module, v, 8, 11, 14, st->st_mtime, mnsec) < 0) {
+        goto error;
+    }
+    if (fill_time(module, v, 9, 12, 15, st->st_ctime, cnsec) < 0) {
+        goto error;
+    }
 
 #ifdef HAVE_STRUCT_STAT_ST_BLKSIZE
-    PyStructSequence_SET_ITEM(v, ST_BLKSIZE_IDX,
-                              PyLong_FromLong((long)st->st_blksize));
+    SET_ITEM(ST_BLKSIZE_IDX, PyLong_FromLong((long)st->st_blksize));
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_BLOCKS
-    PyStructSequence_SET_ITEM(v, ST_BLOCKS_IDX,
-                              PyLong_FromLong((long)st->st_blocks));
+    SET_ITEM(ST_BLOCKS_IDX, PyLong_FromLong((long)st->st_blocks));
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_RDEV
-    PyStructSequence_SET_ITEM(v, ST_RDEV_IDX,
-                              PyLong_FromLong((long)st->st_rdev));
+    SET_ITEM(ST_RDEV_IDX, PyLong_FromLong((long)st->st_rdev));
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_GEN
-    PyStructSequence_SET_ITEM(v, ST_GEN_IDX,
-                              PyLong_FromLong((long)st->st_gen));
+    SET_ITEM(ST_GEN_IDX, PyLong_FromLong((long)st->st_gen));
 #endif
 #if defined(HAVE_STRUCT_STAT_ST_BIRTHTIME)
     {
-      PyObject *val;
-      unsigned long bsec,bnsec;
+      unsigned long bsec, bnsec;
       bsec = (long)st->st_birthtime;
 #ifdef HAVE_STAT_TV_NSEC2
       bnsec = st->st_birthtimespec.tv_nsec;
 #else
       bnsec = 0;
 #endif
-      val = PyFloat_FromDouble(bsec + 1e-9*bnsec);
-      PyStructSequence_SET_ITEM(v, ST_BIRTHTIME_IDX,
-                                val);
+      SET_ITEM(ST_BIRTHTIME_IDX, PyFloat_FromDouble(bsec + bnsec * 1e-9));
     }
 #elif defined(MS_WINDOWS)
-    fill_time(module, v, -1, ST_BIRTHTIME_IDX, ST_BIRTHTIME_NS_IDX,
-              st->st_birthtime, st->st_birthtime_nsec);
+    if (fill_time(module, v, -1, ST_BIRTHTIME_IDX, ST_BIRTHTIME_NS_IDX,
+                  st->st_birthtime, st->st_birthtime_nsec) < 0) {
+        goto error;
+    }
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_FLAGS
-    PyStructSequence_SET_ITEM(v, ST_FLAGS_IDX,
-                              PyLong_FromLong((long)st->st_flags));
+    SET_ITEM(ST_FLAGS_IDX, PyLong_FromLong((long)st->st_flags));
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_FILE_ATTRIBUTES
-    PyStructSequence_SET_ITEM(v, ST_FILE_ATTRIBUTES_IDX,
-                              PyLong_FromUnsignedLong(st->st_file_attributes));
+    SET_ITEM(ST_FILE_ATTRIBUTES_IDX,
+             PyLong_FromUnsignedLong(st->st_file_attributes));
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_FSTYPE
-   PyStructSequence_SET_ITEM(v, ST_FSTYPE_IDX,
-                              PyUnicode_FromString(st->st_fstype));
+   SET_ITEM(ST_FSTYPE_IDX, PyUnicode_FromString(st->st_fstype));
 #endif
 #ifdef HAVE_STRUCT_STAT_ST_REPARSE_TAG
-    PyStructSequence_SET_ITEM(v, ST_REPARSE_TAG_IDX,
-                              PyLong_FromUnsignedLong(st->st_reparse_tag));
+    SET_ITEM(ST_REPARSE_TAG_IDX, PyLong_FromUnsignedLong(st->st_reparse_tag));
 #endif
 
-    if (PyErr_Occurred()) {
-        Py_DECREF(v);
-        return NULL;
-    }
-
+    assert(!PyErr_Occurred());
     return v;
+
+error:
+    Py_DECREF(v);
+    return NULL;
+
+#undef SET_ITEM
 }
 
 /* POSIX methods */