binder: use node->tmp_refs to ensure node safety

When obtaining a node via binder_get_node(),
binder_get_node_from_ref() or binder_new_node(),
increment node->tmp_refs to take a
temporary reference on the node to ensure the node
persists while being used.  binder_put_node() must
be called to remove the temporary reference.

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 104 insertions, 20 deletions

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 4d0b99862339..ec050c6d1192 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -274,6 +274,7 @@ struct binder_node {
         int internal_strong_refs;
         int local_weak_refs;
         int local_strong_refs;
+        int tmp_refs;
         binder_uintptr_t ptr;
         binder_uintptr_t cookie;
         unsigned has_strong_ref:1;
@@ -427,6 +428,7 @@ static void
 binder_defer_work(struct binder_proc *proc, enum binder_deferred_state defer);
 static void binder_free_thread(struct binder_thread *thread);
 static void binder_free_proc(struct binder_proc *proc);
+static void binder_inc_node_tmpref(struct binder_node *node);
 
 static int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
 {
@@ -521,8 +523,15 @@ static struct binder_node *binder_get_node(struct binder_proc *proc,
                         n = n->rb_left;
                 else if (ptr > node->ptr)
                         n = n->rb_right;
-                else
+                else {
+                        /*
+                         * take an implicit weak reference
+                         * to ensure node stays alive until
+                         * call to binder_put_node()
+                         */
+                        binder_inc_node_tmpref(node);
                         return node;
+                }
         }
         return NULL;
 }
@@ -551,6 +560,7 @@ static struct binder_node *binder_new_node(struct binder_proc *proc,
         if (node == NULL)
                 return NULL;
         binder_stats_created(BINDER_STAT_NODE);
+        node->tmp_refs++;
         rb_link_node(&node->rb_node, parent, p);
         rb_insert_color(&node->rb_node, &proc->nodes);
         node->debug_id = atomic_inc_return(&binder_last_id);
@@ -615,7 +625,8 @@ static int binder_dec_node(struct binder_node *node, int strong, int internal)
         } else {
                 if (!internal)
                         node->local_weak_refs--;
-                if (node->local_weak_refs || !hlist_empty(&node->refs))
+                if (node->local_weak_refs || node->tmp_refs ||
+                                !hlist_empty(&node->refs))
                         return 0;
         }
         if (node->proc && (node->has_strong_ref || node->has_weak_ref)) {
@@ -625,7 +636,7 @@ static int binder_dec_node(struct binder_node *node, int strong, int internal)
                 }
         } else {
                 if (hlist_empty(&node->refs) && !node->local_strong_refs &&
-                    !node->local_weak_refs) {
+                    !node->local_weak_refs && !node->tmp_refs) {
                         list_del_init(&node->work.entry);
                         if (node->proc) {
                                 rb_erase(&node->rb_node, &node->proc->nodes);
@@ -648,6 +659,46 @@ static int binder_dec_node(struct binder_node *node, int strong, int internal)
         return 0;
 }
 
+/**
+ * binder_inc_node_tmpref() - take a temporary reference on node
+ * @node:       node to reference
+ *
+ * Take reference on node to prevent the node from being freed
+ * while referenced only by a local variable
+ */
+static void binder_inc_node_tmpref(struct binder_node *node)
+{
+        /*
+         * No call to binder_inc_node() is needed since we
+         * don't need to inform userspace of any changes to
+         * tmp_refs
+         */
+        node->tmp_refs++;
+}
+
+/**
+ * binder_dec_node_tmpref() - remove a temporary reference on node
+ * @node:       node to reference
+ *
+ * Release temporary reference on node taken via binder_inc_node_tmpref()
+ */
+static void binder_dec_node_tmpref(struct binder_node *node)
+{
+        node->tmp_refs--;
+        BUG_ON(node->tmp_refs < 0);
+        /*
+         * Call binder_dec_node() to check if all refcounts are 0
+         * and cleanup is needed. Calling with strong=0 and internal=1
+         * causes no actual reference to be released in binder_dec_node().
+         * If that changes, a change is needed here too.
+         */
+        binder_dec_node(node, 0, 1);
+}
+
+static void binder_put_node(struct binder_node *node)
+{
+        binder_dec_node_tmpref(node);
+}
 
 static struct binder_ref *binder_get_ref(struct binder_proc *proc,
                                          u32 desc, bool need_strong_ref)
@@ -888,6 +939,11 @@ static struct binder_node *binder_get_node_from_ref(
         if (!ref)
                 goto err_no_ref;
         node = ref->node;
+        /*
+         * Take an implicit reference on the node to ensure
+         * it stays alive until the call to binder_put_node()
+         */
+        binder_inc_node_tmpref(node);
         if (rdata)
                 *rdata = ref->data;
 
@@ -1348,6 +1404,7 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
                                      node->debug_id, (u64)node->ptr);
                         binder_dec_node(node, hdr->type == BINDER_TYPE_BINDER,
                                         0);
+                        binder_put_node(node);
                 } break;
                 case BINDER_TYPE_HANDLE:
                 case BINDER_TYPE_WEAK_HANDLE: {
@@ -1441,7 +1498,7 @@ static int binder_translate_binder(struct flat_binder_object *fp,
         struct binder_proc *proc = thread->proc;
         struct binder_proc *target_proc = t->to_proc;
         struct binder_ref_data rdata;
-        int ret;
+        int ret = 0;
 
         node = binder_get_node(proc, fp->binder);
         if (!node) {
@@ -1457,16 +1514,19 @@ static int binder_translate_binder(struct flat_binder_object *fp,
                                   proc->pid, thread->pid, (u64)fp->binder,
                                   node->debug_id, (u64)fp->cookie,
                                   (u64)node->cookie);
-                return -EINVAL;
+                ret = -EINVAL;
+                goto done;
+        }
+        if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+                ret = -EPERM;
+                goto done;
         }
-        if (security_binder_transfer_binder(proc->tsk, target_proc->tsk))
-                return -EPERM;
 
         ret = binder_inc_ref_for_node(target_proc, node,
                         fp->hdr.type == BINDER_TYPE_BINDER,
                         &thread->todo, &rdata);
         if (ret)
-                return ret;
+                goto done;
 
         if (fp->hdr.type == BINDER_TYPE_BINDER)
                 fp->hdr.type = BINDER_TYPE_HANDLE;
@@ -1481,7 +1541,9 @@ static int binder_translate_binder(struct flat_binder_object *fp,
                      "        node %d u%016llx -> ref %d desc %d\n",
                      node->debug_id, (u64)node->ptr,
                      rdata.debug_id, rdata.desc);
-        return 0;
+done:
+        binder_put_node(node);
+        return ret;
 }
 
 static int binder_translate_handle(struct flat_binder_object *fp,
@@ -1492,6 +1554,7 @@ static int binder_translate_handle(struct flat_binder_object *fp,
         struct binder_proc *target_proc = t->to_proc;
         struct binder_node *node;
         struct binder_ref_data src_rdata;
+        int ret = 0;
 
         node = binder_get_node_from_ref(proc, fp->handle,
                         fp->hdr.type == BINDER_TYPE_HANDLE, &src_rdata);
@@ -1500,8 +1563,10 @@ static int binder_translate_handle(struct flat_binder_object *fp,
                                   proc->pid, thread->pid, fp->handle);
                 return -EINVAL;
         }
-        if (security_binder_transfer_binder(proc->tsk, target_proc->tsk))
-                return -EPERM;
+        if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+                ret = -EPERM;
+                goto done;
+        }
 
         if (node->proc == target_proc) {
                 if (fp->hdr.type == BINDER_TYPE_HANDLE)
@@ -1526,7 +1591,7 @@ static int binder_translate_handle(struct flat_binder_object *fp,
                                 fp->hdr.type == BINDER_TYPE_HANDLE,
                                 NULL, &dest_rdata);
                 if (ret)
-                        return ret;
+                        goto done;
 
                 fp->binder = 0;
                 fp->handle = dest_rdata.desc;
@@ -1539,7 +1604,9 @@ static int binder_translate_handle(struct flat_binder_object *fp,
                              dest_rdata.debug_id, dest_rdata.desc,
                              node->debug_id);
         }
-        return 0;
+done:
+        binder_put_node(node);
+        return ret;
 }
 
 static int binder_translate_fd(int fd,
@@ -2381,6 +2448,7 @@ static int binder_thread_write(struct binder_proc *proc,
                                         "BC_INCREFS_DONE" : "BC_ACQUIRE_DONE",
                                         (u64)node_ptr, node->debug_id,
                                         (u64)cookie, (u64)node->cookie);
+                                binder_put_node(node);
                                 break;
                         }
                         if (cmd == BC_ACQUIRE_DONE) {
@@ -2388,6 +2456,7 @@ static int binder_thread_write(struct binder_proc *proc,
                                         binder_user_error("%d:%d BC_ACQUIRE_DONE node %d has no pending acquire request\n",
                                                 proc->pid, thread->pid,
                                                 node->debug_id);
+                                        binder_put_node(node);
                                         break;
                                 }
                                 node->pending_strong_ref = 0;
@@ -2396,16 +2465,19 @@ static int binder_thread_write(struct binder_proc *proc,
                                         binder_user_error("%d:%d BC_INCREFS_DONE node %d has no pending increfs request\n",
                                                 proc->pid, thread->pid,
                                                 node->debug_id);
+                                        binder_put_node(node);
                                         break;
                                 }
                                 node->pending_weak_ref = 0;
                         }
                         binder_dec_node(node, cmd == BC_ACQUIRE_DONE, 0);
                         binder_debug(BINDER_DEBUG_USER_REFS,
-                                     "%d:%d %s node %d ls %d lw %d\n",
+                                     "%d:%d %s node %d ls %d lw %d tr %d\n",
                                      proc->pid, thread->pid,
                                      cmd == BC_INCREFS_DONE ? "BC_INCREFS_DONE" : "BC_ACQUIRE_DONE",
-                                     node->debug_id, node->local_strong_refs, node->local_weak_refs);
+                                     node->debug_id, node->local_strong_refs,
+                                     node->local_weak_refs, node->tmp_refs);
+                        binder_put_node(node);
                         break;
                 }
                 case BC_ATTEMPT_ACQUIRE:
@@ -2845,7 +2917,8 @@ retry:
                         strong = node->internal_strong_refs ||
                                         node->local_strong_refs;
                         weak = !hlist_empty(&node->refs) ||
-                                        node->local_weak_refs || strong;
+                                        node->local_weak_refs ||
+                                        node->tmp_refs || strong;
                         has_strong_ref = node->has_strong_ref;
                         has_weak_ref = node->has_weak_ref;
 
@@ -3357,6 +3430,7 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
         new_node->has_strong_ref = 1;
         new_node->has_weak_ref = 1;
         context->binder_context_mgr_node = new_node;
+        binder_put_node(new_node);
 out:
         mutex_unlock(&context->context_mgr_node_lock);
         return ret;
@@ -3615,8 +3689,11 @@ static int binder_node_release(struct binder_node *node, int refs)
 
         list_del_init(&node->work.entry);
         binder_release_work(&node->async_todo);
-
-        if (hlist_empty(&node->refs)) {
+        /*
+         * The caller must have taken a temporary ref on the node,
+         */
+        BUG_ON(!node->tmp_refs);
+        if (hlist_empty(&node->refs) && node->tmp_refs == 1) {
                 kfree(node);
                 binder_stats_deleted(BINDER_STAT_NODE);
 
@@ -3651,6 +3728,7 @@ static int binder_node_release(struct binder_node *node, int refs)
         binder_debug(BINDER_DEBUG_DEAD_BINDER,
                      "node %d now dead, refs %d, death %d\n",
                      node->debug_id, refs, death);
+        binder_put_node(node);
 
         return refs;
 }
@@ -3700,6 +3778,12 @@ static void binder_deferred_release(struct binder_proc *proc)
 
                 node = rb_entry(n, struct binder_node, rb_node);
                 nodes++;
+                /*
+                 * take a temporary ref on the node before
+                 * calling binder_node_release() which will either
+                 * kfree() the node or call binder_put_node()
+                 */
+                binder_inc_node_tmpref(node);
                 rb_erase(&node->rb_node, &proc->nodes);
                 incoming_refs = binder_node_release(node, incoming_refs);
         }
@@ -3895,11 +3979,11 @@ static void print_binder_node(struct seq_file *m, struct binder_node *node)
         hlist_for_each_entry(ref, &node->refs, node_entry)
                 count++;
 
-        seq_printf(m, "  node %d: u%016llx c%016llx hs %d hw %d ls %d lw %d is %d iw %d",
+        seq_printf(m, "  node %d: u%016llx c%016llx hs %d hw %d ls %d lw %d is %d iw %d tr %d",
                    node->debug_id, (u64)node->ptr, (u64)node->cookie,
                    node->has_strong_ref, node->has_weak_ref,
                    node->local_strong_refs, node->local_weak_refs,
-                   node->internal_strong_refs, count);
+                   node->internal_strong_refs, count, node->tmp_refs);
         if (count) {
                 seq_puts(m, " proc");
                 hlist_for_each_entry(ref, &node->refs, node_entry)