From 4283e6a300b8b05f8fb32dc27dfe0bd774ef16db Mon Sep 17 00:00:00 2001 From: Fam Zheng Date: Fri, 30 May 2014 03:46:55 +0200 Subject: [PATCH 08/13] aio: Fix use-after-free in cancellation path RH-Author: Fam Zheng Message-id: <1401421615-17300-1-git-send-email-famz@redhat.com> Patchwork-id: 59078 O-Subject: [RHEL-7 qemu-kvm PATCH] aio: Fix use-after-free in cancellation path Bugzilla: 1095877 RH-Acked-by: Paolo Bonzini RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Kevin Wolf Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1095877 Brew: https://brewweb.devel.redhat.com/taskinfo?taskID=7519118 (RHEL) https://brewweb.devel.redhat.com/taskinfo?taskID=7519129 (RHEV) 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 (cherry picked from commit 271c0f68b4eae72691721243a1c37f46a3232d61) Signed-off-by: Fam Zheng --- tests/test-thread-pool.c | 2 +- thread-pool.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-) Signed-off-by: Miroslav Rezanina --- tests/test-thread-pool.c | 2 +- thread-pool.c | 1 + 2 files changed, 2 insertions(+), 1 deletions(-) diff --git a/tests/test-thread-pool.c b/tests/test-thread-pool.c index b62338f..1be970d 100644 --- a/tests/test-thread-pool.c +++ b/tests/test-thread-pool.c @@ -181,7 +181,7 @@ static void test_cancel(void) /* Canceling the others will be a blocking operation. */ for (i = 0; i < 100; i++) { - if (data[i].n != 3) { + if (data[i].aiocb && data[i].n != 3) { bdrv_aio_cancel(data[i].aiocb); } } diff --git a/thread-pool.c b/thread-pool.c index 0ebd4c2..fc6a33b 100644 --- a/thread-pool.c +++ b/thread-pool.c @@ -229,6 +229,7 @@ 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 = { -- 1.7.1