1 files changed, 66 insertions, 27 deletions

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index ab34239a76ee..0621a95b8597 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2582,6 +2582,48 @@ static bool binder_proc_transaction(struct binder_transaction *t,
         return true;
 }
 
+/**
+ * binder_get_node_refs_for_txn() - Get required refs on node for txn
+ * @node:         struct binder_node for which to get refs
+ * @proc:         returns @node->proc if valid
+ * @error:        if no @proc then returns BR_DEAD_REPLY
+ *
+ * User-space normally keeps the node alive when creating a transaction
+ * since it has a reference to the target. The local strong ref keeps it
+ * alive if the sending process dies before the target process processes
+ * the transaction. If the source process is malicious or has a reference
+ * counting bug, relying on the local strong ref can fail.
+ *
+ * Since user-space can cause the local strong ref to go away, we also take
+ * a tmpref on the node to ensure it survives while we are constructing
+ * the transaction. We also need a tmpref on the proc while we are
+ * constructing the transaction, so we take that here as well.
+ *
+ * Return: The target_node with refs taken or NULL if no @node->proc is NULL.
+ * Also sets @proc if valid. If the @node->proc is NULL indicating that the
+ * target proc has died, @error is set to BR_DEAD_REPLY
+ */
+static struct binder_node *binder_get_node_refs_for_txn(
+                struct binder_node *node,
+                struct binder_proc **procp,
+                uint32_t *error)
+{
+        struct binder_node *target_node = NULL;
+
+        binder_node_inner_lock(node);
+        if (node->proc) {
+                target_node = node;
+                binder_inc_node_nilocked(node, 1, 0, NULL);
+                binder_inc_node_tmpref_ilocked(node);
+                node->proc->tmp_ref++;
+                *procp = node->proc;
+        } else
+                *error = BR_DEAD_REPLY;
+        binder_node_inner_unlock(node);
+
+        return target_node;
+}
+
 static void binder_transaction(struct binder_proc *proc,
                                struct binder_thread *thread,
                                struct binder_transaction_data *tr, int reply,
@@ -2685,43 +2727,35 @@ static void binder_transaction(struct binder_proc *proc,
                         ref = binder_get_ref_olocked(proc, tr->target.handle,
                                                      true);
                         if (ref) {
-                                binder_inc_node(ref->node, 1, 0, NULL);
-                                target_node = ref->node;
-                        }
-                        binder_proc_unlock(proc);
-                        if (target_node == NULL) {
+                                target_node = binder_get_node_refs_for_txn(
+                                                ref->node, &target_proc,
+                                                &return_error);
+                        } else {
                                 binder_user_error("%d:%d got transaction to invalid handle\n",
-                                        proc->pid, thread->pid);
+                                                  proc->pid, thread->pid);
                                 return_error = BR_FAILED_REPLY;
-                                return_error_param = -EINVAL;
-                                return_error_line = __LINE__;
-                                goto err_invalid_target_handle;
                         }
+                        binder_proc_unlock(proc);
                 } else {
                         mutex_lock(&context->context_mgr_node_lock);
                         target_node = context->binder_context_mgr_node;
-                        if (target_node == NULL) {
+                        if (target_node)
+                                target_node = binder_get_node_refs_for_txn(
+                                                target_node, &target_proc,
+                                                &return_error);
+                        else
                                 return_error = BR_DEAD_REPLY;
-                                mutex_unlock(&context->context_mgr_node_lock);
-                                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;
-                binder_node_lock(target_node);
-                target_proc = target_node->proc;
-                if (target_proc == NULL) {
-                        binder_node_unlock(target_node);
-                        return_error = BR_DEAD_REPLY;
+                if (!target_node) {
+                        /*
+                         * return_error is set above
+                         */
+                        return_error_param = -EINVAL;
                         return_error_line = __LINE__;
                         goto err_dead_binder;
                 }
-                binder_inner_proc_lock(target_proc);
-                target_proc->tmp_ref++;
-                binder_inner_proc_unlock(target_proc);
-                binder_node_unlock(target_node);
+                e->to_node = target_node->debug_id;
                 if (security_binder_transaction(proc->tsk,
                                                 target_proc->tsk) < 0) {
                         return_error = BR_FAILED_REPLY;
@@ -3071,6 +3105,8 @@ static void binder_transaction(struct binder_proc *proc,
         if (target_thread)
                 binder_thread_dec_tmpref(target_thread);
         binder_proc_dec_tmpref(target_proc);
+        if (target_node)
+                binder_dec_node_tmpref(target_node);
         /*
          * write barrier to synchronize with initialization
          * of log entry
@@ -3090,6 +3126,8 @@ err_bad_parent:
 err_copy_data_failed:
         trace_binder_transaction_failed_buffer_release(t->buffer);
         binder_transaction_buffer_release(target_proc, t->buffer, offp);
+        if (target_node)
+                binder_dec_node_tmpref(target_node);
         target_node = NULL;
         t->buffer->transaction = NULL;
         binder_alloc_free_buf(&target_proc->alloc, t->buffer);
@@ -3104,13 +3142,14 @@ err_bad_call_stack:
 err_empty_call_stack:
 err_dead_binder:
 err_invalid_target_handle:
-err_no_context_mgr_node:
         if (target_thread)
                 binder_thread_dec_tmpref(target_thread);
         if (target_proc)
                 binder_proc_dec_tmpref(target_proc);
-        if (target_node)
+        if (target_node) {
                 binder_dec_node(target_node, 1, 0);
+                binder_dec_node_tmpref(target_node);
+        }
 
         binder_debug(BINDER_DEBUG_FAILED_TRANSACTION,
                      "%d:%d transaction failed %d/%d, size %lld-%lld line %d\n",