Re: [PATCH v2] nfsd/nfsd3_proc_readdir: fix buffer count and page pointers

[NeilBrown <neilb@suse.com>]

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On Thu, Apr 04 2019, Murphy Zhou wrote:

> After this commit
>   f875a79 nfsd: allow nfsv3 readdir request to be larger.
> nfsv3 readdir request size can be larger than PAGE_SIZE. So if the
> directory been read is large enough, we can use multiple pages
> in rq_respages. Update buffer count and page pointers like we do
> in readdirplus to make this happen.
>
> Now listing a directory within 3000 files will panic because we
> are counting in a wrong way and would write on random page.
>
> Fixes: f875a79 "nfsd: allow nfsv3 readdir request to be larger"
> Signed-off-by: Murphy Zhou <jencce.kernel@gmail.com>
> ---
>
> v2:
>   fix nfs3svc_decode_readdirargs to set page pointers like decode_readdirplusargs
>   do not test pointers in encode_entry as we've fixed them when decoding
>
>  fs/nfsd/nfs3proc.c | 17 +++++++++++++++--
>  fs/nfsd/nfs3xdr.c  | 11 +++++++++--
>  2 files changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> index 8f933e8..9bc32af 100644
> --- a/fs/nfsd/nfs3proc.c
> +++ b/fs/nfsd/nfs3proc.c
> @@ -442,7 +442,9 @@
>  	struct nfsd3_readdirargs *argp = rqstp->rq_argp;
>  	struct nfsd3_readdirres  *resp = rqstp->rq_resp;
>  	__be32		nfserr;
> -	int		count;
> +	int		count = 0;
> +	struct page	**p;
> +	caddr_t		page_addr = NULL;
>  
>  	dprintk("nfsd: READDIR(3)  %s %d bytes at %d\n",
>  				SVCFH_fmt(&argp->fh),
> @@ -462,7 +464,18 @@
>  	nfserr = nfsd_readdir(rqstp, &resp->fh, (loff_t*) &argp->cookie, 
>  					&resp->common, nfs3svc_encode_entry);
>  	memcpy(resp->verf, argp->verf, 8);
> -	resp->count = resp->buffer - argp->buffer;
> +	count = 0;

Thanks - looks good.
Setting 'count' to zero a second time looks a bit clumsy, but that is a
minor detail.

 Reviewed-by: NeilBrown <neilb@suse.com>

Thanks,
NeilBrown


> +	for (p = rqstp->rq_respages + 1; p < rqstp->rq_next_page; p++) {
> +		page_addr = page_address(*p);
> +
> +		if (((caddr_t)resp->buffer >= page_addr) &&
> +		    ((caddr_t)resp->buffer < page_addr + PAGE_SIZE)) {
> +			count += (caddr_t)resp->buffer - page_addr;
> +			break;
> +		}
> +		count += PAGE_SIZE;
> +	}
> +	resp->count = count >> 2;
>  	if (resp->offset) {
>  		loff_t offset = argp->cookie;
>  
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index 93fea24..8d78912 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -573,6 +573,7 @@ void fill_post_wcc(struct svc_fh *fhp)
>  nfs3svc_decode_readdirargs(struct svc_rqst *rqstp, __be32 *p)
>  {
>  	struct nfsd3_readdirargs *args = rqstp->rq_argp;
> +	int len;
>  	u32 max_blocksize = svc_max_payload(rqstp);
>  
>  	p = decode_fh(p, &args->fh);
> @@ -582,8 +583,14 @@ void fill_post_wcc(struct svc_fh *fhp)
>  	args->verf   = p; p += 2;
>  	args->dircount = ~0;
>  	args->count  = ntohl(*p++);
> -	args->count  = min_t(u32, args->count, max_blocksize);
> -	args->buffer = page_address(*(rqstp->rq_next_page++));
> +	len = args->count  = min_t(u32, args->count, max_blocksize);
> +
> +	while (len > 0) {
> +		struct page *p = *(rqstp->rq_next_page++);
> +		if (!args->buffer)
> +			args->buffer = page_address(p);
> +		len -= PAGE_SIZE;
> +	}
>  
>  	return xdr_argsize_check(rqstp, p);
>  }
> -- 
> 1.8.3.1

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