add memory protection for at_quick_exit

libc/upstream-freebsd/lib/libc/stdlib/quick_exit.c

@@ -28,6 +28,10 @@
 
 #include <stdlib.h>
 #include <pthread.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "private/bionic_prctl.h"
 
 /**
  * Linked list of quick exit handlers.  This is simpler than the atexit()
@@ -39,6 +43,10 @@ struct quick_exit_handler {
 	void (*cleanup)(void);
 };
 
+static struct quick_exit_handler *pool_page;
+static struct quick_exit_handler *pool;
+static size_t pool_size;
+
 /**
  * Lock protecting the handlers list.
  */
@@ -51,16 +59,39 @@ static struct quick_exit_handler *handlers;
 int
 at_quick_exit(void (*func)(void))
 {
+	size_t page_size = getpagesize();
 	struct quick_exit_handler *h;
-
-	h = malloc(sizeof(*h));
 
-	if (NULL == h)
-		return (1);
-	h->cleanup = func;
 	pthread_mutex_lock(&atexit_mutex);
+
+	if (pool_size < sizeof(*h)) {
+		void *ptr = mmap(NULL, page_size, PROT_READ|PROT_WRITE,
+		    MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+		if (ptr == MAP_FAILED) {
+			pthread_mutex_unlock(&atexit_mutex);
+			return (1);
+		}
+		prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ptr, page_size,
+		    "at_quick_exit handlers");
+		pool_page = pool = ptr;
+		pool_size = page_size;
+	} else {
+		if (mprotect(pool_page, page_size, PROT_READ|PROT_WRITE)) {
+			pthread_mutex_unlock(&atexit_mutex);
+			return (1);
+		}
+	}
+
+	h = pool++;
+	pool_size -= sizeof(*h);
+
+	h->cleanup = func;
+
 	h->next = handlers;
 	handlers = h;
+
+	mprotect(pool_page, page_size, PROT_READ);
+
 	pthread_mutex_unlock(&atexit_mutex);
 	return (0);
 }