SUNRPC: double free xprt_ctxt while still in use

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>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 84e5d7d31481bd579e5c09496ff128d2a1e0564d..5fd94f6bdc75d64a9a2fecb51cafbe2826964e94 100644 (file)
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1223,13 +1223,14 @@ static struct cache_deferred_req *svc_defer(struct cache_req *req)
                dr->daddr = rqstp->rq_daddr;
                dr->argslen = rqstp->rq_arg.len >> 2;
                dr->xprt_ctxt = rqstp->rq_xprt_ctxt;
-               rqstp->rq_xprt_ctxt = NULL;
 
                /* back up head to the start of the buffer and copy */
                skip = 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 != dr->xprt_ctxt);
+       rqstp->rq_xprt_ctxt = NULL;
        trace_svc_defer(rqstp);
        svc_xprt_get(rqstp->rq_xprt);
        dr->xprt = rqstp->rq_xprt;