Re: [PATCH] xprtrdma: Store RDMA credits in unsigned variables

[Trond Myklebust <trond.myklebust@primarydata.com>]

On Thu, 2015-02-12 at 10:14 -0500, Chuck Lever wrote:
> Dan Carpenter's static checker pointed out:
> 
>    net/sunrpc/xprtrdma/rpc_rdma.c:879 rpcrdma_reply_handler()
>    warn: can 'credits' be negative?
> 
> "credits" is defined as an int. The credits value comes from the
> server as a 32-bit unsigned integer.
> 
> A malicious or broken server can plant a large unsigned integer in
> that field which would result in an underflow in the following
> logic, potentially triggering a deadlock of the mount point by
> blocking the client from issuing more RPC requests.
> 
> net/sunrpc/xprtrdma/rpc_rdma.c:
> 
>   876          credits = be32_to_cpu(headerp->rm_credit);
>   877          if (credits == 0)
>   878                  credits = 1;    /* don't deadlock */
>   879          else if (credits > r_xprt->rx_buf.rb_max_requests)
>   880                  credits = r_xprt->rx_buf.rb_max_requests;
>   881
>   882          cwnd = xprt->cwnd;
>   883          xprt->cwnd = credits << RPC_CWNDSHIFT;
>   884          if (xprt->cwnd > cwnd)
>   885                  xprt_release_rqst_cong(rqst->rq_task);
> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Fixes: eba8ff660b2d ("xprtrdma: Move credit update to RPC . . .")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/xprtrdma/rpc_rdma.c  |    3 ++-
>  net/sunrpc/xprtrdma/xprt_rdma.h |    2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index 7e9acd9..91ffde8 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -738,8 +738,9 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
>  	struct rpc_xprt *xprt = rep->rr_xprt;
>  	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
>  	__be32 *iptr;
> -	int credits, rdmalen, status;
> +	int rdmalen, status;
>  	unsigned long cwnd;
> +	u32 credits;
>  
>  	/* Check status. If bad, signal disconnect and return rep to pool */
>  	if (rep->rr_len == ~0U) {
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index d1b7039..0a16fb6 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -285,7 +285,7 @@ rpcr_to_rdmar(struct rpc_rqst *rqst)
>   */
>  struct rpcrdma_buffer {
>  	spinlock_t	rb_lock;	/* protects indexes */
> -	int		rb_max_requests;/* client max requests */
> +	u32		rb_max_requests;/* client max requests */
>  	struct list_head rb_mws;	/* optional memory windows/fmrs/frmrs */
>  	struct list_head rb_all;
>  	int		rb_send_index;
> 

Anna, do you want me to take this one directly, or are you preparing a
pull request?

Cheers
  Trond