Allocate red zone and stack space together and then split red zone from

allocated space, orignal code left red zone unallocated, but those space
can be allocated by user code, and result was providing no protection.

1 files changed, 17 insertions, 7 deletions

diff --git a/lib/libpthread/thread/thr_stack.c b/lib/libpthread/thread/thr_stack.c
index 9714593..484eb81 100644
--- a/lib/libpthread/thread/thr_stack.c
+++ b/lib/libpthread/thread/thr_stack.c
@@ -61,7 +61,7 @@ static LIST_HEAD(, stack)	mstackq = LIST_HEAD_INITIALIZER(mstackq);
  * Base address of the last stack allocated (including its red zone, if
  * there is one).  Stacks are allocated contiguously, starting beyond the
  * top of the main stack.  When a new stack is created, a red zone is
- * typically created (actually, the red zone is simply left unmapped) above
+ * typically created (actually, the red zone is mapped with PROT_NONE) above
  * the top of the stack, such that the stack will not be able to grow all
  * the way to the bottom of the next stack.  This isn't fool-proof.  It is
  * possible for a stack to grow by a large amount, such that it grows into
@@ -134,6 +134,7 @@ _thr_stack_alloc(struct pthread_attr *attr)
 	kse_critical_t crit;
 	size_t stacksize;
 	size_t guardsize;
+	char *stackaddr;
 
 	/*
 	 * Round up stack size to nearest multiple of _thr_page_size so
@@ -194,7 +195,7 @@ _thr_stack_alloc(struct pthread_attr *attr)
 			    _thr_guard_default;
 
 		/* Allocate a new stack. */
-		attr->stackaddr_attr = last_stack - stacksize;
+		stackaddr = last_stack - stacksize - guardsize;
 
 		/*
 		 * Even if stack allocation fails, we don't want to try to
@@ -209,11 +210,20 @@ _thr_stack_alloc(struct pthread_attr *attr)
 		KSE_LOCK_RELEASE(curkse, &_thread_list_lock);
 		_kse_critical_leave(crit);
 
-		/* Map the stack, but not the guard page: */
-		if ((attr->stackaddr_attr = mmap(attr->stackaddr_attr,
-		     stacksize, PROT_READ | PROT_WRITE, MAP_STACK,
-		     -1, 0)) == MAP_FAILED)
-			attr->stackaddr_attr = NULL;
+		/* Map the stack and guard page together, and split guard
+		   page from allocated space: */
+		if ((stackaddr = mmap(stackaddr, stacksize+guardsize,
+		     PROT_READ | PROT_WRITE, MAP_STACK,
+		     -1, 0)) != MAP_FAILED &&
+		    (guardsize == 0 ||
+		     mprotect(stackaddr, guardsize, PROT_NONE) == 0)) {
+			stackaddr += guardsize;
+		} else {
+			if (stackaddr != MAP_FAILED)
+				munmap(stackaddr, stacksize + guardsize);
+			stackaddr = NULL;
+		}
+		attr->stackaddr_attr = stackaddr;
 	}
 	if (attr->stackaddr_attr != NULL)
 		return (0);