From: Todd Kjos <tkjos@xxxxxxxxxxx>
commit a370003cc301d4361bae20c9ef615f89bf8d1e8a upstream
There is a race between the binder driver cleaning
up a completed transaction via binder_free_transaction()
and a user calling binder_ioctl(BC_FREE_BUFFER) to
release a buffer. It doesn't matter which is first but
they need to be protected against running concurrently
which can result in a UAF.
Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.14 4.19
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/android/binder.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 5d67f5fec6c1b..2decb1a5a8e2f 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1960,8 +1960,18 @@ static struct binder_thread *binder_get_txn_from_and_acq_inner(
static void binder_free_transaction(struct binder_transaction *t)
{
- if (t->buffer)
- t->buffer->transaction = NULL;
+ struct binder_proc *target_proc = t->to_proc;
+
+ if (target_proc) {
+ binder_inner_proc_lock(target_proc);
+ if (t->buffer)
+ t->buffer->transaction = NULL;
+ binder_inner_proc_unlock(target_proc);
+ }
+ /*
+ * If the transaction has no target_proc, then
+ * t->buffer->transaction has already been cleared.
+ */
kfree(t);
binder_stats_deleted(BINDER_STAT_TRANSACTION);
}
@@ -3484,10 +3494,12 @@ static int binder_thread_write(struct binder_proc *proc,
buffer->debug_id,
buffer->transaction ? "active" : "finished");
+ binder_inner_proc_lock(proc);
if (buffer->transaction) {
buffer->transaction->buffer = NULL;
buffer->transaction = NULL;
}
+ binder_inner_proc_unlock(proc);
if (buffer->async_transaction && buffer->target_node) {
struct binder_node *buf_node;
struct binder_work *w;
--
2.22.0.709.g102302147b-goog
