From 271c0f68b4eae72691721243a1c37f46a3232d61 Mon Sep 17 00:00:00 2001 From: Fam Zheng Date: Wed, 21 May 2014 10:42:13 +0800 Subject: aio: Fix use-after-free in cancellation path The current flow of canceling a thread from THREAD_ACTIVE state is: 1) Caller wants to cancel a request, so it calls thread_pool_cancel. 2) thread_pool_cancel waits on the conditional variable elem->check_cancel. 3) The worker thread changes state to THREAD_DONE once the task is done, and notifies elem->check_cancel to allow thread_pool_cancel to continue execution, and signals the notifier (pool->notifier) to allow callback function to be called later. But because of the global mutex, the notifier won't get processed until step 4) and 5) are done. 4) thread_pool_cancel continues, leaving the notifier signaled, it just returns to caller. 5) Caller thinks the request is already canceled successfully, so it releases any related data, such as freeing elem->common.opaque. 6) In the next main loop iteration, the notifier handler, event_notifier_ready, is called. It finds the canceled thread in THREAD_DONE state, so calls elem->common.cb, with an (likely) dangling opaque pointer. This is a use-after-free. Fix it by calling event_notifier_ready before leaving thread_pool_cancel. Test case update: This change will let cancel complete earlier than test-thread-pool.c expects, so update the code to check this case: if it's already done, done_cb sets .aiocb to NULL, skip calling bdrv_aio_cancel on them. Reported-by: Ulrich Obergfell Suggested-by: Paolo Bonzini Signed-off-by: Fam Zheng Signed-off-by: Stefan Hajnoczi --- thread-pool.c | 1 + 1 file changed, 1 insertion(+) (limited to 'thread-pool.c') diff --git a/thread-pool.c b/thread-pool.c index fbdd3ffa3a..dfb699dd94 100644 --- a/thread-pool.c +++ b/thread-pool.c @@ -224,6 +224,7 @@ static void thread_pool_cancel(BlockDriverAIOCB *acb) pool->pending_cancellations--; } qemu_mutex_unlock(&pool->lock); + event_notifier_ready(&pool->notifier); } static const AIOCBInfo thread_pool_aiocb_info = { -- cgit v1.2.3