Re: [PATCH] nfsd: check for oversized NFSv2/v3 arguments

["J. Bruce Fields" <bfields@fieldses.org>]

(Cc'd you, Neil, partly on the off chance you might have a better idea
where this came from.  Looks to me like it may have been there forever,
but, I haven't looked too hard yet.)

--b.

On Fri, Apr 14, 2017 at 11:04:40AM -0400, bfields wrote:
> From: "J. Bruce Fields" <bfields@redhat.com>
> 
> A client can append random data to the end of an NFSv2 or NFSv3 RPC call
> without our complaining; we'll just stop parsing at the end of the
> expected data and ignore the rest.
> 
> Encoded arguments and replies are stored together in an array of pages,
> and if a call is too large it could leave inadequate space for the
> reply.  This is normally OK because NFS RPC's typically have either
> short arguments and long replies (like READ) or long arguments and short
> replies (like WRITE).  But a client that sends an incorrectly long reply
> can violate those assumptions.  This was observed to cause crashes.
> 
> So, insist that the argument not be any longer than we expect.
> 
> Also, several operations increment rq_next_page in the decode routine
> before checking the argument size, which can leave rq_next_page pointing
> well past the end of the page array, causing trouble later in
> svc_free_pages.
> 
> As followup we may also want to rewrite the encoding routines to check
> more carefully that they aren't running off the end of the page array.
> 
> Reported-by: Tuomas Haanpää <thaan@synopsys.com>
> Reported-by: Ari Kauppi <ari@synopsys.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
> ---
>  fs/nfsd/nfs3xdr.c          | 23 +++++++++++++++++------
>  fs/nfsd/nfsxdr.c           | 13 ++++++++++---
>  include/linux/sunrpc/svc.h |  3 +--
>  3 files changed, 28 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index dba2ff8eaa68..be66bcadfaea 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -334,8 +334,11 @@ nfs3svc_decode_readargs(struct svc_rqst *rqstp, __be32 *p,
>  	if (!p)
>  		return 0;
>  	p = xdr_decode_hyper(p, &args->offset);
> -
>  	args->count = ntohl(*p++);
> +
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
> +
>  	len = min(args->count, max_blocksize);
>  
>  	/* set up the kvec */
> @@ -349,7 +352,7 @@ nfs3svc_decode_readargs(struct svc_rqst *rqstp, __be32 *p,
>  		v++;
>  	}
>  	args->vlen = v;
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  int
> @@ -536,9 +539,11 @@ nfs3svc_decode_readlinkargs(struct svc_rqst *rqstp, __be32 *p,
>  	p = decode_fh(p, &args->fh);
>  	if (!p)
>  		return 0;
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
>  	args->buffer = page_address(*(rqstp->rq_next_page++));
>  
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  int
> @@ -564,10 +569,14 @@ nfs3svc_decode_readdirargs(struct svc_rqst *rqstp, __be32 *p,
>  	args->verf   = p; p += 2;
>  	args->dircount = ~0;
>  	args->count  = ntohl(*p++);
> +
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
> +
>  	args->count  = min_t(u32, args->count, PAGE_SIZE);
>  	args->buffer = page_address(*(rqstp->rq_next_page++));
>  
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  int
> @@ -585,6 +594,9 @@ nfs3svc_decode_readdirplusargs(struct svc_rqst *rqstp, __be32 *p,
>  	args->dircount = ntohl(*p++);
>  	args->count    = ntohl(*p++);
>  
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
> +
>  	len = args->count = min(args->count, max_blocksize);
>  	while (len > 0) {
>  		struct page *p = *(rqstp->rq_next_page++);
> @@ -592,8 +604,7 @@ nfs3svc_decode_readdirplusargs(struct svc_rqst *rqstp, __be32 *p,
>  			args->buffer = page_address(p);
>  		len -= PAGE_SIZE;
>  	}
> -
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  int
> diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
> index 41b468a6a90f..79268369f7b3 100644
> --- a/fs/nfsd/nfsxdr.c
> +++ b/fs/nfsd/nfsxdr.c
> @@ -257,6 +257,9 @@ nfssvc_decode_readargs(struct svc_rqst *rqstp, __be32 *p,
>  	len = args->count     = ntohl(*p++);
>  	p++; /* totalcount - unused */
>  
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
> +
>  	len = min_t(unsigned int, len, NFSSVC_MAXBLKSIZE_V2);
>  
>  	/* set up somewhere to store response.
> @@ -272,7 +275,7 @@ nfssvc_decode_readargs(struct svc_rqst *rqstp, __be32 *p,
>  		v++;
>  	}
>  	args->vlen = v;
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  int
> @@ -360,9 +363,11 @@ nfssvc_decode_readlinkargs(struct svc_rqst *rqstp, __be32 *p, struct nfsd_readli
>  	p = decode_fh(p, &args->fh);
>  	if (!p)
>  		return 0;
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
>  	args->buffer = page_address(*(rqstp->rq_next_page++));
>  
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  int
> @@ -400,9 +405,11 @@ nfssvc_decode_readdirargs(struct svc_rqst *rqstp, __be32 *p,
>  	args->cookie = ntohl(*p++);
>  	args->count  = ntohl(*p++);
>  	args->count  = min_t(u32, args->count, PAGE_SIZE);
> +	if (!xdr_argsize_check(rqstp, p))
> +		return 0;
>  	args->buffer = page_address(*(rqstp->rq_next_page++));
>  
> -	return xdr_argsize_check(rqstp, p);
> +	return 1;
>  }
>  
>  /*
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index e770abeed32d..6ef19cf658b4 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -336,8 +336,7 @@ xdr_argsize_check(struct svc_rqst *rqstp, __be32 *p)
>  {
>  	char *cp = (char *)p;
>  	struct kvec *vec = &rqstp->rq_arg.head[0];
> -	return cp >= (char*)vec->iov_base
> -		&& cp <= (char*)vec->iov_base + vec->iov_len;
> +	return cp == (char *)vec->iov_base + vec->iov_len;
>  }
>  
>  static inline int
> -- 
> 2.9.3
>