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vdpa: Fix possible use-after-free for VirtQueueElement

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QEMU uses vhost_handle_guest_kick() to forward guest's available
buffers to the vdpa device in SVQ avail ring.

In vhost_handle_guest_kick(), a `g_autofree` `elem` is used to
iterate through the available VirtQueueElements. This `elem` is
then passed to `svq->ops->avail_handler`, specifically to the
vhost_vdpa_net_handle_ctrl_avail(). If this handler fails to
process the CVQ command, vhost_handle_guest_kick() regains
ownership of the `elem`, and either frees it or requeues it.

Yet the problem is that, vhost_vdpa_net_handle_ctrl_avail()
mistakenly frees the `elem`, even if it fails to forward the
CVQ command to vdpa device. This can result in a use-after-free
for the `elem` in vhost_handle_guest_kick().

This patch solves this problem by refactoring
vhost_vdpa_net_handle_ctrl_avail() to only freeing the `elem` if
it owns it.

Fixes: bd907ae4b0 ("vdpa: manual forward CVQ buffers")
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
Message-Id: <e3f2d7db477734afe5c6a5ab3fa8b8317514ea34.1688746840.git.yin31149@gmail.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Hawkins Jiawei 2023-07-08 00:44:42 +08:00 committed by Michael S. Tsirkin
parent 625b370c45
commit 031b1abacb
1 changed files with 10 additions and 1 deletions
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11
net/vhost-vdpa.c
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@ -831,7 +831,16 @@ out:
error_report("Bad device CVQ written length");
}
vhost_svq_push_elem(svq, elem, MIN(in_len, sizeof(status)));
g_free(elem);
/*
* `elem` belongs to vhost_vdpa_net_handle_ctrl_avail() only when
* the function successfully forwards the CVQ command, indicated
* by a non-negative value of `dev_written`. Otherwise, it still
* belongs to SVQ.
* This function should only free the `elem` when it owns.
*/
if (dev_written >= 0) {
g_free(elem);
}
return dev_written < 0 ? dev_written : 0;
}