gh-100227: Lock Around Adding Global Audit Hooks (gh-105515)

The risk of a race with this state is relatively low, but we play it safe anyway.

1 files changed, 39 insertions, 17 deletions

diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 4427e73..7027410 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -168,7 +168,7 @@ should_audit(PyInterpreterState *interp)
     if (!interp) {
         return 0;
     }
-    return (interp->runtime->audit_hook_head
+    return (interp->runtime->audit_hooks.head
             || interp->audit_hooks
             || PyDTrace_AUDIT_ENABLED());
 }
@@ -224,8 +224,11 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
         goto exit;
     }
 
-    /* Call global hooks */
-    _Py_AuditHookEntry *e = is->runtime->audit_hook_head;
+    /* Call global hooks
+     *
+     * We don't worry about any races on hooks getting added,
+     * since that would not leave is in an inconsistent state. */
+    _Py_AuditHookEntry *e = is->runtime->audit_hooks.head;
     for (; e; e = e->next) {
         if (e->hookCFunction(event, eventArgs, e->userData) < 0) {
             goto exit;
@@ -353,8 +356,12 @@ _PySys_ClearAuditHooks(PyThreadState *ts)
     _PySys_Audit(ts, "cpython._PySys_ClearAuditHooks", NULL);
     _PyErr_Clear(ts);
 
-    _Py_AuditHookEntry *e = runtime->audit_hook_head, *n;
-    runtime->audit_hook_head = NULL;
+    /* We don't worry about the very unlikely race right here,
+     * since it's entirely benign.  Nothing else removes entries
+     * from the list and adding an entry right now would not cause
+     * any trouble. */
+    _Py_AuditHookEntry *e = runtime->audit_hooks.head, *n;
+    runtime->audit_hooks.head = NULL;
     while (e) {
         n = e->next;
         PyMem_RawFree(e);
@@ -362,6 +369,22 @@ _PySys_ClearAuditHooks(PyThreadState *ts)
     }
 }
 
+static void
+add_audit_hook_entry_unlocked(_PyRuntimeState *runtime,
+                              _Py_AuditHookEntry *entry)
+{
+    if (runtime->audit_hooks.head == NULL) {
+        runtime->audit_hooks.head = entry;
+    }
+    else {
+        _Py_AuditHookEntry *last = runtime->audit_hooks.head;
+        while (last->next) {
+            last = last->next;
+        }
+        last->next = entry;
+    }
+}
+
 int
 PySys_AddAuditHook(Py_AuditHookFunction hook, void *userData)
 {
@@ -389,29 +412,28 @@ PySys_AddAuditHook(Py_AuditHookFunction hook, void *userData)
         }
     }
 
-    _Py_AuditHookEntry *e = runtime->audit_hook_head;
-    if (!e) {
-        e = (_Py_AuditHookEntry*)PyMem_RawMalloc(sizeof(_Py_AuditHookEntry));
-        runtime->audit_hook_head = e;
-    } else {
-        while (e->next) {
-            e = e->next;
-        }
-        e = e->next = (_Py_AuditHookEntry*)PyMem_RawMalloc(
+    _Py_AuditHookEntry *e = (_Py_AuditHookEntry*)PyMem_RawMalloc(
             sizeof(_Py_AuditHookEntry));
-    }
-
     if (!e) {
         if (tstate != NULL) {
             _PyErr_NoMemory(tstate);
         }
         return -1;
     }
-
     e->next = NULL;
     e->hookCFunction = (Py_AuditHookFunction)hook;
     e->userData = userData;
 
+    if (runtime->audit_hooks.mutex == NULL) {
+        /* The runtime must not be initailized yet. */
+        add_audit_hook_entry_unlocked(runtime, e);
+    }
+    else {
+        PyThread_acquire_lock(runtime->audit_hooks.mutex, WAIT_LOCK);
+        add_audit_hook_entry_unlocked(runtime, e);
+        PyThread_release_lock(runtime->audit_hooks.mutex);
+    }
+
     return 0;
 }