From: Todd Kjos Date: Wed, 12 Jun 2019 20:29:27 +0000 (-0700) Subject: binder: fix possible UAF when freeing buffer X-Git-Tag: v4.14.136~17 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a4a3c070b8760f71c8311399fa9bfe67c8629bca;p=thirdparty%2Fkernel%2Fstable.git binder: fix possible UAF when freeing buffer 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 Cc: stable Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/android/binder.c b/drivers/android/binder.c index e694fd2c4ed0f..05e75d18b4d93 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -1903,8 +1903,18 @@ 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); } @@ -3426,10 +3436,12 @@ 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;