linux-kernel - Re: [PATCH] fs: nfsd: Fix three possible null-pointer dereferences

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Date:   Tue, 30 Jul 2019 19:03:39 -0400
From:   "J. Bruce Fields" <bfields@...ldses.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     chuck.lever@...cle.com, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: nfsd: Fix three possible null-pointer dereferences

On Wed, Jul 24, 2019 at 04:28:03PM +0800, Jia-Ju Bai wrote:
> In nfs4_xdr_dec_cb_recall(), nfs4_xdr_dec_cb_layout() and
> nfs4_xdr_dec_cb_notify_lock(), there is an if statement to check whether
> cb is NULL.
> 
> When cb is NULL, the three functions all call:
>     decode_cb_op_status(..., &cb->cb_status);
> 
> Thus, possible null-pointer dereferences may occur.
> 
> To fix these possible bugs, -EINVAL is returned when cb is NULL.
> 
> These bugs are found by a static analysis tool STCheck written by us.

Thanks!  But I think actually the correct fix is just to remove the NULL
checks entirely.

--b.

> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  fs/nfsd/nfs4callback.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> index 397eb7820929..55949a158b6b 100644
> --- a/fs/nfsd/nfs4callback.c
> +++ b/fs/nfsd/nfs4callback.c
> @@ -516,7 +516,8 @@ static int nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp,
>  		status = decode_cb_sequence4res(xdr, cb);
>  		if (unlikely(status || cb->cb_seq_status))
>  			return status;
> -	}
> +	} else
> +		return -EINVAL;
>  
>  	return decode_cb_op_status(xdr, OP_CB_RECALL, &cb->cb_status);
>  }
> @@ -608,7 +609,9 @@ static int nfs4_xdr_dec_cb_layout(struct rpc_rqst *rqstp,
>  		status = decode_cb_sequence4res(xdr, cb);
>  		if (unlikely(status || cb->cb_seq_status))
>  			return status;
> -	}
> +	} else
> +		return -EINVAL;
> +
>  	return decode_cb_op_status(xdr, OP_CB_LAYOUTRECALL, &cb->cb_status);
>  }
>  #endif /* CONFIG_NFSD_PNFS */
> @@ -667,7 +670,9 @@ static int nfs4_xdr_dec_cb_notify_lock(struct rpc_rqst *rqstp,
>  		status = decode_cb_sequence4res(xdr, cb);
>  		if (unlikely(status || cb->cb_seq_status))
>  			return status;
> -	}
> +	} else
> +		return -EINVAL;
> +	
>  	return decode_cb_op_status(xdr, OP_CB_NOTIFY_LOCK, &cb->cb_status);
>  }
>  
> -- 
> 2.17.0