On Fri, 2016-10-28 at 22:22 -0400, Chuck Lever wrote:
> The underlying transport releases the page pointed to by rq_buffer
> during xprt_rdma_bc_send_request. When the backchannel reply arrives,
> rq_rbuffer then points to freed memory.
>
> Fixes: 68778945e46f ('SUNRPC: Separate buffer pointers for RPC ...')
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> Hi Bruce-
>
> This applies on top of Jeff's recent patch in the same area. It's
> an obvious quick fix rather than a deep review of that code path.
>
> I've tested with iozone, git "make test", and some xfstests with
> NFSv4.1 / RDMA; I ran into another crasher that is preventing more
> extensive testing. The prepare_creds crash has not re-appeared so
> far.
>
> I enabled RPC client debugging on the server during these tests to
> confirm that the CB_RECALL operations were successful.
>
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> index fc4535e..20027f8 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> @@ -177,19 +177,26 @@ static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
> return -EINVAL;
> }
>
> + /* svc_rdma_sendto releases this page */
> page = alloc_page(RPCRDMA_DEF_GFP);
> if (!page)
> return -ENOMEM;
> -
> rqst->rq_buffer = page_address(page);
> - rqst->rq_rbuffer = (char *)rqst->rq_buffer + rqst->rq_callsize;
> +
> + rqst->rq_rbuffer = kmalloc(rqst->rq_rcvsize, RPCRDMA_DEF_GFP);
> + if (!rqst->rq_rbuffer) {
> + put_page(page);
> + return -ENOMEM;
> + }
> return 0;
> }
>
> static void
> xprt_rdma_bc_free(struct rpc_task *task)
> {
> - /* No-op: ctxt and page have already been freed. */
> + struct rpc_rqst *rqst = task->tk_rqstp;
> +
> + kfree(rqst->rq_rbuffer);
> }
>
> static int
>
> --
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Obviously, mine was not based on any deep reading of this code either,
so I'll take your word for it on this:
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
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