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To:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>
From:   Vasily Averin <vvs@virtuozzo.com>
Subject: unsafe req->rq_xprt using inside bc_svc_process() ?
Message-ID: <79494560-1876-494a-0838-cc646eabf68c@virtuozzo.com>
Date:   Fri, 29 Nov 2019 17:10:47 +0300
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OpenVz team got complain on crash in bc_svc_process().
Crashed node had 15 running containers with active nfsv4.1 mounts,
single nfsv4.1-svc thread was processed its back-channel requests.
In our case nfs41_callback_svc() took rpc_rqst *req from serv->sv_cb_list
started its processing but found that req->rq_xprt points to already freed
struct rpc_xprt aka part of struct sock_xprt transport.

Back-channel request was submitted via xprt_complete_bc_request(),
its processing uses req->rq_xprt reference in many times,
however I did not found who keeps this reference.
It seems sock_xprt or even whole its net namespace can be freed before bc_svc_process() will start processing of submitted back-channel request, and req->rq_xprt using is unsafe in bc_svc_process()

Am I missed something probably?

Thank you,
	Vasily Averin