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Commit 6c65c2d2 authored by Todd Kjos's avatar Todd Kjos Committed by shaohanlin
Browse files

binder: fix possible UAF when freeing buffer 



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: default avatarTodd Kjos <tkjos@google.com>
parent 904bba25

drivers/android/binder.c

+14 −2
Original line number Diff line number Diff line
@@ -2116,8 +2116,18 @@ static struct binder_thread *binder_get_txn_from_and_acq_inner( 


static void binder_free_transaction(struct binder_transaction *t)

{

	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);

}
@@ -3656,10 +3666,12 @@ 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;