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From:   "NeilBrown" <neilb@suse.de>
To:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH 1/2] SUNRPC: double free xprt_ctxt while still in use
Date:   Tue, 09 May 2023 09:41:49 +1000
Message-id: <168358930939.26026.4067210924697967164@noble.neil.brown.name>
Precedence: bulk


When an RPC request is deferred, the rq_xprt_ctxt pointer is moved out
of the svc_rqst into the svc_deferred_req.
When the deferred request is revisited, the pointer is copied into
the new svc_rqst - and also remains in the svc_deferred_req.

In the (rare?) case that the request is deferred a second time, the old
svc_deferred_req is reused - it still has all the correct content.
However in that case the rq_xprt_ctxt pointer is NOT cleared so that
when xpo_release_xprt is called, the ctxt is freed (UDP) or possible
added to a free list (RDMA).
When the deferred request is revisited for a second time, it will
reference this ctxt which may be invalid, and the free the object a
second time which is likely to oops.

So change svc_defer() to *always* clear rq_xprt_ctxt, and assert that
the value is now stored in the svc_deferred_req.

Fixes: 773f91b2cf3f ("SUNRPC: Fix NFSD's request deferral on RDMA transports")
Signed-off-by: NeilBrown <neilb@suse.de>
---
 net/sunrpc/svc_xprt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 84e5d7d31481..5fd94f6bdc75 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1223,13 +1223,14 @@ static struct cache_deferred_req *svc_defer(struct ca=
che_req *req)
 		dr->daddr =3D rqstp->rq_daddr;
 		dr->argslen =3D rqstp->rq_arg.len >> 2;
 		dr->xprt_ctxt =3D rqstp->rq_xprt_ctxt;
-		rqstp->rq_xprt_ctxt =3D NULL;
=20
 		/* back up head to the start of the buffer and copy */
 		skip =3D rqstp->rq_arg.len - rqstp->rq_arg.head[0].iov_len;
 		memcpy(dr->args, rqstp->rq_arg.head[0].iov_base - skip,
 		       dr->argslen << 2);
 	}
+	WARN_ON_ONCE(rqstp->rq_xprt_ctxt !=3D dr->xprt_ctxt);
+	rqstp->rq_xprt_ctxt =3D NULL;
 	trace_svc_defer(rqstp);
 	svc_xprt_get(rqstp->rq_xprt);
 	dr->xprt =3D rqstp->rq_xprt;
--=20
2.40.1