From: Stefan Hajnoczi <stefanha@redhat.com>
To: qemu-devel@nongnu.org
Cc: Fam Zheng <fam@euphon.net>,
Peter Maydell <peter.maydell@linaro.org>,
qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: [Qemu-devel] [PULL 1/2] util/async: hold AioContext ref to prevent use-after-free
Date: Thu, 22 Aug 2019 16:53:01 +0100 [thread overview]
Message-ID: <20190822155302.20916-2-stefanha@redhat.com> (raw)
In-Reply-To: <20190822155302.20916-1-stefanha@redhat.com>
The tests/test-bdrv-drain /bdrv-drain/iothread/drain test case does the
following:
1. The preadv coroutine calls aio_bh_schedule_oneshot() and then yields.
2. The one-shot BH executes in another AioContext. All it does is call
aio_co_wakeup(preadv_co).
3. The preadv coroutine is re-entered and returns.
There is a race condition in aio_co_wake() where the preadv coroutine
returns and the test case destroys the preadv IOThread. aio_co_wake()
can still be running in the other AioContext and it performs an access
to the freed IOThread AioContext.
Here is the race in aio_co_schedule():
QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
co, co_scheduled_next);
<-- race: co may execute before we invoke qemu_bh_schedule()!
qemu_bh_schedule(ctx->co_schedule_bh);
So if co causes ctx to be freed then we're in trouble. Fix this problem
by holding a reference to ctx.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20190723190623.21537-1-stefanha@redhat.com
Message-Id: <20190723190623.21537-1-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
util/async.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/util/async.c b/util/async.c
index 8d2105729c..4e4c7af51e 100644
--- a/util/async.c
+++ b/util/async.c
@@ -459,9 +459,17 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co)
abort();
}
+ /* The coroutine might run and release the last ctx reference before we
+ * invoke qemu_bh_schedule(). Take a reference to keep ctx alive until
+ * we're done.
+ */
+ aio_context_ref(ctx);
+
QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
co, co_scheduled_next);
qemu_bh_schedule(ctx->co_schedule_bh);
+
+ aio_context_unref(ctx);
}
void aio_co_wake(struct Coroutine *co)
--
2.21.0
next prev parent reply other threads:[~2019-08-22 15:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 15:53 [Qemu-devel] [PULL 0/2] Block patches Stefan Hajnoczi
2019-08-22 15:53 ` Stefan Hajnoczi [this message]
2019-08-22 15:53 ` [Qemu-devel] [PULL 2/2] vhost-user-scsi: prevent using uninitialized vqs Stefan Hajnoczi
2019-08-27 9:00 ` [Qemu-devel] [PULL 0/2] Block patches Peter Maydell
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