ANDROID: binder: Add strong ref checks

BugLink: http://bugs.launchpad.net/bugs/1642572

commit 0a3ffab9 upstream.

Prevent using a binder_ref with only weak references where a strong
reference is required.
Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Martijn Coenen <maco@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/android/binder.c

@@ -1003,7 +1003,7 @@ static int binder_dec_node(struct binder_node *node, int strong, int internal)
 
 
 static struct binder_ref *binder_get_ref(struct binder_proc *proc,
-					 uint32_t desc)
+					 u32 desc, bool need_strong_ref)
 {
 	struct rb_node *n = proc->refs_by_desc.rb_node;
 	struct binder_ref *ref;
@@ -1011,13 +1011,17 @@ static struct binder_ref *binder_get_ref(struct binder_proc *proc,
 	while (n) {
 		ref = rb_entry(n, struct binder_ref, rb_node_desc);
 
-		if (desc < ref->desc)
+		if (desc < ref->desc) {
 			n = n->rb_left;
-		else if (desc > ref->desc)
+		} else if (desc > ref->desc) {
 			n = n->rb_right;
-		else
+		} else if (need_strong_ref && !ref->strong) {
+			binder_user_error("tried to use weak ref as strong ref\n");
+			return NULL;
+		} else {
 			return ref;
 		}
+	}
 	return NULL;
 }
 
@@ -1286,7 +1290,10 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
 		} break;
 		case BINDER_TYPE_HANDLE:
 		case BINDER_TYPE_WEAK_HANDLE: {
-			struct binder_ref *ref = binder_get_ref(proc, fp->handle);
+			struct binder_ref *ref;
+
+			ref = binder_get_ref(proc, fp->handle,
+					     fp->type == BINDER_TYPE_HANDLE);
 
 			if (ref == NULL) {
 				pr_err("transaction release %d bad handle %d\n",
@@ -1380,7 +1387,7 @@ static void binder_transaction(struct binder_proc *proc,
 		if (tr->target.handle) {
 			struct binder_ref *ref;
 
-			ref = binder_get_ref(proc, tr->target.handle);
+			ref = binder_get_ref(proc, tr->target.handle, true);
 			if (ref == NULL) {
 				binder_user_error("%d:%d got transaction to invalid handle\n",
 					proc->pid, thread->pid);
@@ -1583,7 +1590,10 @@ static void binder_transaction(struct binder_proc *proc,
 		} break;
 		case BINDER_TYPE_HANDLE:
 		case BINDER_TYPE_WEAK_HANDLE: {
-			struct binder_ref *ref = binder_get_ref(proc, fp->handle);
+			struct binder_ref *ref;
+
+			ref = binder_get_ref(proc, fp->handle,
+					     fp->type == BINDER_TYPE_HANDLE);
 
 			if (ref == NULL) {
 				binder_user_error("%d:%d got transaction with invalid handle, %d\n",
@@ -1794,7 +1804,9 @@ static int binder_thread_write(struct binder_proc *proc,
 						ref->desc);
 				}
 			} else
-				ref = binder_get_ref(proc, target);
+				ref = binder_get_ref(proc, target,
+						     cmd == BC_ACQUIRE ||
+						     cmd == BC_RELEASE);
 			if (ref == NULL) {
 				binder_user_error("%d:%d refcount change on invalid ref %d\n",
 					proc->pid, thread->pid, target);
@@ -1990,7 +2002,7 @@ static int binder_thread_write(struct binder_proc *proc,
 			if (get_user(cookie, (binder_uintptr_t __user *)ptr))
 				return -EFAULT;
 			ptr += sizeof(binder_uintptr_t);
-			ref = binder_get_ref(proc, target);
+			ref = binder_get_ref(proc, target, false);
 			if (ref == NULL) {
 				binder_user_error("%d:%d %s invalid ref %d\n",
 					proc->pid, thread->pid,