Use Py_CLEAR instead of Py_DECREF to also set the variable to NULL (#1616)

These files contain loops that convert system data into python objects
and during the process they create objects and dereference their
refcounts after they have been added to the resulting list.

However, in case of errors during the creation of those python objects,
the refcount to previously allocated objects is dropped again with
Py_XDECREF, which should be a no-op in case the paramater is NULL. Even
so, in most of these loops the variables pointing to the objects are
never set to NULL, even after Py_DECREF is called at the end of the loop
iteration. This means, after the first iteration, if an error occurs
those python objects will get their refcount dropped two times,
resulting in a possible double-free.

6 files changed, 97 insertions, 101 deletions

diff --git a/psutil/_psutil_aix.c b/psutil/_psutil_aix.c
index 8c055a43..9f58f606 100644
--- a/psutil/_psutil_aix.c
+++ b/psutil/_psutil_aix.c
@@ -265,8 +265,8 @@ psutil_proc_environ(PyObject *self, PyObject *args) {
                 goto error;
             if (PyDict_SetItem(py_retdict, py_key, py_val))
                 goto error;
-            Py_DECREF(py_key);
-            Py_DECREF(py_val);
+            Py_CLEAR(py_key);
+            Py_CLEAR(py_val);
         }
         curvar = strchr(curvar, '\0') + 1;
     }
@@ -510,10 +510,10 @@ psutil_users(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
     endutxent();
 
@@ -570,9 +570,9 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_dev);
-        Py_DECREF(py_mountp);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_dev);
+        Py_CLEAR(py_mountp);
+        Py_CLEAR(py_tuple);
         mt = getmntent(file);
     }
     endmntent(file);
diff --git a/psutil/_psutil_bsd.c b/psutil/_psutil_bsd.c
index 33bb0c2d..e07ddcc1 100644
--- a/psutil/_psutil_bsd.c
+++ b/psutil/_psutil_bsd.c
@@ -154,7 +154,7 @@ psutil_pids(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_pid))
                 goto error;
-            Py_DECREF(py_pid);
+            Py_CLEAR(py_pid);
             proclist++;
         }
         free(orig_address);
@@ -507,8 +507,8 @@ psutil_proc_open_files(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_tuple))
                 goto error;
-            Py_DECREF(py_path);
-            Py_DECREF(py_tuple);
+            Py_CLEAR(py_path);
+            Py_CLEAR(py_tuple);
         }
     }
     free(freep);
@@ -670,9 +670,9 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_dev);
-        Py_DECREF(py_mountp);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_dev);
+        Py_CLEAR(py_mountp);
+        Py_CLEAR(py_tuple);
     }
 
     free(fs);
@@ -765,7 +765,7 @@ psutil_net_io_counters(PyObject *self, PyObject *args) {
                 goto error;
             if (PyDict_SetItemString(py_retdict, ifc_name, py_ifc_info))
                 goto error;
-            Py_DECREF(py_ifc_info);
+            Py_CLEAR(py_ifc_info);
         }
         else {
             continue;
@@ -840,10 +840,10 @@ psutil_users(PyObject *self, PyObject *args) {
             fclose(fp);
             goto error;
         }
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
 
     fclose(fp);
@@ -883,10 +883,10 @@ psutil_users(PyObject *self, PyObject *args) {
             endutxent();
             goto error;
         }
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
 
     endutxent();
diff --git a/psutil/_psutil_linux.c b/psutil/_psutil_linux.c
index 717723d0..0d16eb42 100644
--- a/psutil/_psutil_linux.c
+++ b/psutil/_psutil_linux.c
@@ -241,9 +241,9 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_dev);
-        Py_DECREF(py_mountp);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_dev);
+        Py_CLEAR(py_mountp);
+        Py_CLEAR(py_tuple);
     }
     endmntent(file);
     return py_retlist;
@@ -454,10 +454,10 @@ psutil_users(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
     endutent();
     return py_retlist;
diff --git a/psutil/_psutil_osx.c b/psutil/_psutil_osx.c
index d2ca94b5..76ec0ee8 100644
--- a/psutil/_psutil_osx.c
+++ b/psutil/_psutil_osx.c
@@ -138,7 +138,7 @@ psutil_pids(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_pid))
             goto error;
-        Py_DECREF(py_pid);
+        Py_CLEAR(py_pid);
         proclist++;
     }
     free(orig_address);
@@ -653,7 +653,7 @@ psutil_per_cpu_times(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_cputime))
             goto error;
-        Py_DECREF(py_cputime);
+        Py_CLEAR(py_cputime);
     }
 
     ret = vm_deallocate(mach_task_self(), (vm_address_t)info_array,
@@ -841,9 +841,9 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_dev);
-        Py_DECREF(py_mountp);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_dev);
+        Py_CLEAR(py_mountp);
+        Py_CLEAR(py_tuple);
     }
 
     free(fs);
@@ -911,7 +911,6 @@ psutil_proc_threads(PyObject *self, PyObject *args) {
     }
 
     for (j = 0; j < thread_count; j++) {
-        py_tuple = NULL;
         thread_info_count = THREAD_INFO_MAX;
         kr = thread_info(thread_list[j], THREAD_BASIC_INFO,
                          (thread_info_t)thinfo_basic, &thread_info_count);
@@ -934,7 +933,7 @@ psutil_proc_threads(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_tuple);
     }
 
     ret = vm_deallocate(task, (vm_address_t)thread_list,
@@ -1043,10 +1042,8 @@ psutil_proc_open_files(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_tuple))
                 goto error;
-            Py_DECREF(py_tuple);
-            py_tuple = NULL;
-            Py_DECREF(py_path);
-            py_path = NULL;
+            Py_CLEAR(py_tuple);
+            Py_CLEAR(py_path);
             // --- /construct python list
         }
     }
@@ -1226,7 +1223,7 @@ psutil_proc_connections(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
+                Py_CLEAR(py_tuple);
             }
             else if (family == AF_UNIX) {
                 py_laddr = PyUnicode_DecodeFSDefault(
@@ -1248,9 +1245,9 @@ psutil_proc_connections(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
-                Py_DECREF(py_laddr);
-                Py_DECREF(py_raddr);
+                Py_CLEAR(py_tuple);
+                Py_CLEAR(py_laddr);
+                Py_CLEAR(py_raddr);
             }
         }
     }
@@ -1370,7 +1367,7 @@ psutil_net_io_counters(PyObject *self, PyObject *args) {
                 goto error;
             if (PyDict_SetItemString(py_retdict, ifc_name, py_ifc_info))
                 goto error;
-            Py_DECREF(py_ifc_info);
+            Py_CLEAR(py_ifc_info);
         }
         else {
             continue;
@@ -1543,7 +1540,7 @@ psutil_disk_io_counters(PyObject *self, PyObject *args) {
                 goto error;
             if (PyDict_SetItemString(py_retdict, disk_name, py_disk_info))
                 goto error;
-            Py_DECREF(py_disk_info);
+            Py_CLEAR(py_disk_info);
 
             CFRelease(parent_dict);
             IOObjectRelease(parent);
@@ -1605,10 +1602,10 @@ psutil_users(PyObject *self, PyObject *args) {
             endutxent();
             goto error;
         }
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
 
     endutxent();
diff --git a/psutil/_psutil_sunos.c b/psutil/_psutil_sunos.c
index 919e76d6..31d6f364 100644
--- a/psutil/_psutil_sunos.c
+++ b/psutil/_psutil_sunos.c
@@ -300,8 +300,8 @@ psutil_proc_environ(PyObject *self, PyObject *args) {
         if (PyDict_SetItem(py_retdict, py_envname, py_envval) < 0)
             goto error;
 
-        Py_DECREF(py_envname);
-        Py_DECREF(py_envval);
+        Py_CLEAR(py_envname);
+        Py_CLEAR(py_envval);
     }
 
     psutil_free_cstrings_array(env, env_count);
@@ -655,10 +655,10 @@ psutil_users(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_username);
-        Py_DECREF(py_tty);
-        Py_DECREF(py_hostname);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
     }
     endutxent();
 
@@ -714,9 +714,9 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_dev);
-        Py_DECREF(py_mountp);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_dev);
+        Py_CLEAR(py_mountp);
+        Py_CLEAR(py_tuple);
     }
     fclose(file);
     return py_retlist;
@@ -767,8 +767,7 @@ psutil_per_cpu_times(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_cputime))
                 goto error;
-            Py_DECREF(py_cputime);
-            py_cputime = NULL;
+            Py_CLEAR(py_cputime);
         }
     }
 
@@ -824,7 +823,7 @@ psutil_disk_io_counters(PyObject *self, PyObject *args) {
                 if (PyDict_SetItemString(py_retdict, ksp->ks_name,
                                          py_disk_info))
                     goto error;
-                Py_DECREF(py_disk_info);
+                Py_CLEAR(py_disk_info);
             }
         }
         ksp = ksp->ks_next;
@@ -959,8 +958,8 @@ psutil_proc_memory_maps(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_path);
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_path);
+        Py_CLEAR(py_tuple);
 
         // increment pointer
         p += 1;
@@ -1075,7 +1074,7 @@ psutil_net_io_counters(PyObject *self, PyObject *args) {
             goto error;
         if (PyDict_SetItemString(py_retdict, ksp->ks_name, py_ifc_info))
             goto error;
-        Py_DECREF(py_ifc_info);
+        Py_CLEAR(py_ifc_info);
         goto next;
 
 next:
@@ -1273,7 +1272,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
+                Py_CLEAR(py_tuple);
             }
         }
 #if defined(AF_INET6)
@@ -1287,7 +1286,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
 #ifdef NEW_MIB_COMPLIANT
                 processed_pid = tp6.tcp6ConnCreationProcess;
 #else
-        		processed_pid = 0;
+                        processed_pid = 0;
 #endif
                 if (pid != -1 && processed_pid != pid)
                     continue;
@@ -1316,14 +1315,14 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
+                Py_CLEAR(py_tuple);
             }
         }
 #endif
         // UDPv4
         else if (mibhdr.level == MIB2_UDP || mibhdr.level == MIB2_UDP_ENTRY) {
             num_ent = mibhdr.len / sizeof(mib2_udpEntry_t);
-	    assert(num_ent * sizeof(mib2_udpEntry_t) == mibhdr.len);
+            assert(num_ent * sizeof(mib2_udpEntry_t) == mibhdr.len);
             for (i = 0; i < num_ent; i++) {
                 memcpy(&ude, databuf.buf + i * sizeof ude, sizeof ude);
 #ifdef NEW_MIB_COMPLIANT
@@ -1355,7 +1354,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
+                Py_CLEAR(py_tuple);
             }
         }
 #if defined(AF_INET6)
@@ -1388,7 +1387,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
+                Py_CLEAR(py_tuple);
             }
         }
 #endif
@@ -1561,7 +1560,7 @@ psutil_net_if_stats(PyObject* self, PyObject* args) {
                 goto error;
             if (PyDict_SetItemString(py_retdict, ksp->ks_name, py_ifc_info))
                 goto error;
-            Py_DECREF(py_ifc_info);
+            Py_CLEAR(py_ifc_info);
         }
     }
 
diff --git a/psutil/_psutil_windows.c b/psutil/_psutil_windows.c
index beaba183..08b208dc 100644
--- a/psutil/_psutil_windows.c
+++ b/psutil/_psutil_windows.c
@@ -221,7 +221,7 @@ psutil_pids(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_pid))
             goto error;
-        Py_DECREF(py_pid);
+        Py_CLEAR(py_pid);
     }
 
     // free C array allocated for PIDs
@@ -1003,7 +1003,7 @@ psutil_per_cpu_times(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_tuple);
     }
 
     free(sppi);
@@ -1156,7 +1156,7 @@ psutil_proc_threads(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_tuple))
                 goto error;
-            Py_DECREF(py_tuple);
+            Py_CLEAR(py_tuple);
 
             CloseHandle(hThread);
         }
@@ -1580,7 +1580,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_conn_tuple))
                 goto error;
-            Py_DECREF(py_conn_tuple);
+            Py_CLEAR(py_conn_tuple);
         }
 
         free(table);
@@ -1667,7 +1667,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_conn_tuple))
                 goto error;
-            Py_DECREF(py_conn_tuple);
+            Py_CLEAR(py_conn_tuple);
         }
 
         free(table);
@@ -1730,7 +1730,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_conn_tuple))
                 goto error;
-            Py_DECREF(py_conn_tuple);
+            Py_CLEAR(py_conn_tuple);
         }
 
         free(table);
@@ -1793,7 +1793,7 @@ psutil_net_connections(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_conn_tuple))
                 goto error;
-            Py_DECREF(py_conn_tuple);
+            Py_CLEAR(py_conn_tuple);
         }
 
         free(table);
@@ -2188,8 +2188,8 @@ psutil_net_io_counters(PyObject *self, PyObject *args) {
             goto error;
         if (PyDict_SetItem(py_retdict, py_nic_name, py_nic_info))
             goto error;
-        Py_XDECREF(py_nic_name);
-        Py_XDECREF(py_nic_info);
+        Py_CLEAR(py_nic_name);
+        Py_CLEAR(py_nic_info);
 
         free(pIfRow);
         pCurrAddresses = pCurrAddresses->Next;
@@ -2304,7 +2304,7 @@ psutil_disk_io_counters(PyObject *self, PyObject *args) {
             goto error;
         if (PyDict_SetItemString(py_retdict, szDeviceDisplay, py_tuple))
             goto error;
-        Py_XDECREF(py_tuple);
+        Py_CLEAR(py_tuple);
 
 next:
         CloseHandle(hDevice);
@@ -2461,7 +2461,7 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
                             goto error;
                         }
 
-                        Py_DECREF(py_tuple);
+                        Py_CLEAR(py_tuple);
 
                         // Continue looking for more mount points
                         mp_flag = FindNextVolumeMountPoint(mp_h, mp_buf, MAX_PATH);
@@ -2486,7 +2486,7 @@ psutil_disk_partitions(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_DECREF(py_tuple);
+        Py_CLEAR(py_tuple);
         goto next;
 
 next:
@@ -2610,9 +2610,9 @@ psutil_users(PyObject *self, PyObject *args) {
             goto error;
         if (PyList_Append(py_retlist, py_tuple))
             goto error;
-        Py_XDECREF(py_username);
-        Py_XDECREF(py_address);
-        Py_XDECREF(py_tuple);
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_address);
+        Py_CLEAR(py_tuple);
     }
 
     WTSFreeMemory(sessions);
@@ -2838,8 +2838,8 @@ psutil_proc_memory_maps(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_tuple))
                 goto error;
-            Py_DECREF(py_tuple);
-            Py_DECREF(py_str);
+            Py_CLEAR(py_tuple);
+            Py_CLEAR(py_str);
         }
         previousAllocationBase = (ULONGLONG)basicInfo.AllocationBase;
         baseAddress = (PCHAR)baseAddress + basicInfo.RegionSize;
@@ -2889,8 +2889,8 @@ psutil_ppid_map(PyObject *self, PyObject *args) {
                 goto error;
             if (PyDict_SetItem(py_retdict, py_pid, py_ppid))
                 goto error;
-            Py_DECREF(py_pid);
-            Py_DECREF(py_ppid);
+            Py_CLEAR(py_pid);
+            Py_CLEAR(py_ppid);
         } while (Process32Next(handle, &pe));
     }
 
@@ -2993,8 +2993,8 @@ psutil_net_if_addrs(PyObject *self, PyObject *args) {
                 goto error;
             if (PyList_Append(py_retlist, py_tuple))
                 goto error;
-            Py_DECREF(py_tuple);
-            Py_DECREF(py_mac_address);
+            Py_CLEAR(py_tuple);
+            Py_CLEAR(py_mac_address);
         }
 
         // find out the IP address associated with the NIC
@@ -3070,14 +3070,14 @@ psutil_net_if_addrs(PyObject *self, PyObject *args) {
                     goto error;
                 if (PyList_Append(py_retlist, py_tuple))
                     goto error;
-                Py_DECREF(py_tuple);
-                Py_DECREF(py_address);
-                Py_DECREF(py_netmask);
+                Py_CLEAR(py_tuple);
+                Py_CLEAR(py_address);
+                Py_CLEAR(py_netmask);
 
                 pUnicast = pUnicast->Next;
             }
         }
-        Py_DECREF(py_nic_name);
+        Py_CLEAR(py_nic_name);
         pCurrAddresses = pCurrAddresses->Next;
     }
 
@@ -3197,8 +3197,8 @@ psutil_net_if_stats(PyObject *self, PyObject *args) {
             goto error;
         if (PyDict_SetItem(py_retdict, py_nic_name, py_ifc_info))
             goto error;
-        Py_DECREF(py_nic_name);
-        Py_DECREF(py_ifc_info);
+        Py_CLEAR(py_nic_name);
+        Py_CLEAR(py_ifc_info);
     }
 
     free(pIfTable);