FROMLIST: binder: make sure target_node has strong ref

(from https://patchwork.kernel.org/patch/9817787/)

When initiating a transaction, the target_node must
have a strong ref on it. Then we take a second
strong ref to make sure the node survives until the
transaction is complete.

Change-Id: Ia77b1794a92a8b6b8a564e48b4a4a6b225b5c279
Signed-off-by: Todd Kjos <tkjos@google.com>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 1e1306a2913672747febb82961f069770203603f..f0172af190acb992c4cfc9d9c93139c7892aa7d5 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1469,8 +1469,19 @@ static void binder_transaction(struct binder_proc *proc,
                if (tr->target.handle) {
                        struct binder_ref *ref;
 
+                       /*
+                        * There must already be a strong ref
+                        * on this node. If so, do a strong
+                        * increment on the node to ensure it
+                        * stays alive until the transaction is
+                        * done.
+                        */
                        ref = binder_get_ref(proc, tr->target.handle, true);
-                       if (ref == NULL) {
+                       if (ref) {
+                               binder_inc_node(ref->node, 1, 0, NULL);
+                               target_node = ref->node;
+                       }
+                       if (target_node == NULL) {
                                binder_user_error("%d:%d got transaction to invalid handle\n",
                                        proc->pid, thread->pid);
                                return_error = BR_FAILED_REPLY;
@@ -1478,7 +1489,6 @@ static void binder_transaction(struct binder_proc *proc,
                                return_error_line = __LINE__;
                                goto err_invalid_target_handle;
                        }
-                       target_node = ref->node;
                } else {
                        mutex_lock(&context->context_mgr_node_lock);
                        target_node = context->binder_context_mgr_node;
@@ -1488,6 +1498,7 @@ static void binder_transaction(struct binder_proc *proc,
                                return_error_line = __LINE__;
                                goto err_no_context_mgr_node;
                        }
+                       binder_inc_node(target_node, 1, 0, NULL);
                        mutex_unlock(&context->context_mgr_node_lock);
                }
                e->to_node = target_node->debug_id;
@@ -1608,9 +1619,6 @@ static void binder_transaction(struct binder_proc *proc,
        t->buffer->transaction = t;
        t->buffer->target_node = target_node;
        trace_binder_transaction_alloc_buf(t->buffer);
-       if (target_node)
-               binder_inc_node(target_node, 1, 0, NULL);
-
        off_start = (binder_size_t *)(t->buffer->data +
                                      ALIGN(tr->data_size, sizeof(void *)));
        offp = off_start;
@@ -1846,6 +1854,7 @@ err_bad_parent:
 err_copy_data_failed:
        trace_binder_transaction_failed_buffer_release(t->buffer);
        binder_transaction_buffer_release(target_proc, t->buffer, offp);
+       target_node = NULL;
        t->buffer->transaction = NULL;
        binder_alloc_free_buf(&target_proc->alloc, t->buffer);
 err_binder_alloc_buf_failed:
@@ -1860,6 +1869,9 @@ err_empty_call_stack:
 err_dead_binder:
 err_invalid_target_handle:
 err_no_context_mgr_node:
+       if (target_node)
+               binder_dec_node(target_node, 1, 0);
+
        binder_debug(BINDER_DEBUG_FAILED_TRANSACTION,
                     "%d:%d transaction failed %d/%d, size %lld-%lld line %d\n",
                     proc->pid, thread->pid, return_error, return_error_param,