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authorFam Zheng <famz@redhat.com>2014-05-21 10:42:13 +0800
committerStefan Hajnoczi <stefanha@redhat.com>2014-05-28 14:28:46 +0200
commit271c0f68b4eae72691721243a1c37f46a3232d61 (patch)
tree70ea4e56b2f6705022b0c5979bb1564829d9dda6 /thread-pool.c
parentbd60436936ecebf2c683eef9ea561f2b949700f3 (diff)
downloadqemu-arm-271c0f68b4eae72691721243a1c37f46a3232d61.tar.gz
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 <uobergfe@redhat.com> Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Fam Zheng <famz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'thread-pool.c')
-rw-r--r--thread-pool.c1
1 files changed, 1 insertions, 0 deletions
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 = {