[PATCH 25/37] binder: use node->tmp_refs to ensure node safety

From: Todd Kjos
Date: Thu Jun 29 2017 - 15:08:32 EST

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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@xxxxxxxxxx>
---
drivers/android/binder.c | 124 +++++++++++++++++++++++++++++++++++++++--------
1 file 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 @@ static int binder_thread_read(struct binder_proc *proc,
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)
--
2.13.2.725.g09c95d1e9-goog

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