[PATCH] D58221: [msan] Don't delete MSanAtExitRecord

[Vitaly Buka via Phabricator via llvm-commits]

vitalybuka created this revision.
vitalybuka added a reviewer: eugenis.
Herald added subscribers: llvm-commits, Sanitizers, jdoerfert, jfb.
Herald added projects: Sanitizers, LLVM.

Pre 2.27 libc can run same atexit handler twice
We will keep MSanAtExitRecord and reset fun to mark it as executed.

Fix PR40162


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D58221

Files:
  compiler-rt/lib/msan/msan_interceptors.cc
  compiler-rt/test/msan/cxa_atexit_race.cc


Index: compiler-rt/test/msan/cxa_atexit_race.cc
===================================================================
--- /dev/null
+++ compiler-rt/test/msan/cxa_atexit_race.cc
@@ -0,0 +1,28 @@
+// RUN: %clang_msan %s -o %t && not %run %t 2>&1 | FileCheck %s
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+extern "C" int
+__cxa_atexit(void (*func)(void *), void *arg, void *d);
+
+void handler(void *) {
+}
+
+void *thread(void *) {
+  for (;;)
+    __cxa_atexit(&handler, 0, (void *)&handler);
+}
+
+int main(void) {
+  printf("TEST_MAIN\n");
+  pthread_t pt;
+  for (int i = 0; i < 2; ++i)
+    pthread_create(&pt, 0, &thread, 0);
+  sleep(1);
+  return 1;
+}
+// CHECK: TEST_MAIN
+// CHECK-NOT: MemorySanitizer
Index: compiler-rt/lib/msan/msan_interceptors.cc
===================================================================
--- compiler-rt/lib/msan/msan_interceptors.cc
+++ compiler-rt/lib/msan/msan_interceptors.cc
@@ -1118,8 +1118,12 @@
 void MSanCxaAtExitWrapper(void *arg) {
   UnpoisonParam(1);
   MSanAtExitRecord *r = (MSanAtExitRecord *)arg;
+  // libc before 2.27 had race which caused occasional double handler execution
+  // https://sourceware.org/ml/libc-alpha/2017-08/msg01204.html
+  if (!r->func)
+    return;
   r->func(r->arg);
-  InternalFree(r);
+  r->func = nullptr;
 }
 
 static int setup_at_exit_wrapper(void(*f)(), void *arg, void *dso);


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