RE: [PATCH] svcrdma: Fix NFS server crash triggered by 1MB NFS WRITE

["Steve Wise" <swise@opengridcomputing.com>]

> -----Original Message-----
> From: linux-nfs-owner@vger.kernel.org [mailto:linux-nfs-owner@vger.kernel.org] On Behalf Of Chuck Lever
> Sent: Sunday, October 04, 2015 10:03 PM
> To: linux-nfs@vger.kernel.org; linux-rdma@vger.kernel.org
> Subject: [PATCH] svcrdma: Fix NFS server crash triggered by 1MB NFS WRITE
> 
> Now that the NFS server advertises a maximum payload size of 1MB
> for RPC/RDMA again, it crashes in svc_process_common() when NFS
> client sends a 1MB NFS WRITE on an NFS/RDMA mount.
> 
> The server has set up a 259 element array of struct page pointers
> in rq_pages[] for each incoming request. The last element of the
> array is NULL.
> 
> When an incoming request has been completely received,
> rdma_read_complete() attempts to set the starting page of the
> incoming page vector:
> 
>   rqstp->rq_arg.pages = &rqstp->rq_pages[head->hdr_count];
> 
> and the page to use for the reply:
> 
>   rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
> 
> But the value of page_no has already accounted for head->hdr_count.
> Thus rq_respages now points past the end of the incoming pages. For
> NFS WRITE operations smaller than the maximum, this is harmless.
> 
> But when the NFS WRITE operation is as large as the server's max
> payload size, rq_respages now points at the last entry in rq_pages,
> which is NULL.
> 
> Fixes: cc9a903d915c ('svcrdma: Change maximum server payload . . .')
> BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=270
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> 
> This fixes a 4.3-rc regression. Please apply to 4.3-rc when this
> patch passes review.
> 
> It could also be appropriate for stable kernels which do not have
> commit 7e5be28827bf ("svcrdma: advertise the correct max payload"),
> though I have not tested them with this patch.
> 
>  net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index cb51742..37b4341 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -531,7 +531,7 @@ static int rdma_read_complete(struct svc_rqst *rqstp,
>  	rqstp->rq_arg.page_base = head->arg.page_base;
> 
>  	/* rq_respages starts after the last arg page */
> -	rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
> +	rqstp->rq_respages = &rqstp->rq_pages[page_no];
>  	rqstp->rq_next_page = rqstp->rq_respages + 1;
> 
>  	/* Rebuild rq_arg head and tail. */
> 

Reviewed-by: Steve Wise <swise@opengridcomputing.com>