[PATCH v2] NFSv4: fix getacl ERANGE for some ACL buffer sizes

[Weston Andros Adamson <dros@netapp.com>]

Fix a bug where getxattr returns ERANGE when the attr buffer
length is close enough to the nearest PAGE_SIZE multiple that adding
the extra bytes leaves too little room for the ACL buffer.

Besides storing the ACL buffer, the getacl decoder uses the inline
pages for the attr bitmap and buffer length. __nfs4_get_acl_uncached
must allocate enough page space for all of the data to be decoded.

This patch uses xdr_partial_copy_from_skb to allocate any needed
pages past the first one. This allows the client to always cache the acl
on the first getacl call and not just if it fits in one page.

Signed-off-by: Weston Andros Adamson <dros@netapp.com>
---

Version 2 of this patch changes things up a bit:

 - rely on xdr_partial_copy_from_skb to allocate pages as needed
 - always allocate 1 page as there will be some data
 - allow xdr_partial_copy_from_skb to allocate up to NFS4ACL_MAXPAGES + 1 pages
   to hold the max size ACL and the extra page for the bitmap and acl length
 - this allows the first request for an ACL to be cached - not just when it
   fits in one page

 fs/nfs/nfs4proc.c | 40 +++++++++++++++-------------------------
 fs/nfs/nfs4xdr.c  |  2 --
 2 files changed, 15 insertions(+), 27 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index ca36d0d..dc8e4f5 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -4430,20 +4430,17 @@ out:
 /*
  * The getxattr API returns the required buffer length when called with a
  * NULL buf. The NFSv4 acl tool then calls getxattr again after allocating
- * the required buf.  On a NULL buf, we send a page of data to the server
- * guessing that the ACL request can be serviced by a page. If so, we cache
- * up to the page of ACL data, and the 2nd call to getxattr is serviced by
- * the cache. If not so, we throw away the page, and cache the required
- * length. The next getxattr call will then produce another round trip to
- * the server, this time with the input buf of the required size.
+ * the required buf. Cache the result from the first getxattr call to avoid
+ * sending another RPC.
  */
 static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t buflen)
 {
-	struct page *pages[NFS4ACL_MAXPAGES] = {NULL, };
+	/* enough pages to hold ACL data plus the bitmap and acl length */
+	struct page *pages[NFS4ACL_MAXPAGES + 1] = {NULL, };
 	struct nfs_getaclargs args = {
 		.fh = NFS_FH(inode),
+		/* The xdr layer may allocate pages here. */
 		.acl_pages = pages,
-		.acl_len = buflen,
 	};
 	struct nfs_getaclres res = {
 		.acl_len = buflen,
@@ -4453,32 +4450,25 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 		.rpc_argp = &args,
 		.rpc_resp = &res,
 	};
-	unsigned int npages = DIV_ROUND_UP(buflen, PAGE_SIZE);
 	int ret = -ENOMEM, i;
 
-	/* As long as we're doing a round trip to the server anyway,
-	 * let's be prepared for a page of acl data. */
-	if (npages == 0)
-		npages = 1;
-	if (npages > ARRAY_SIZE(pages))
-		return -ERANGE;
-
-	for (i = 0; i < npages; i++) {
-		pages[i] = alloc_page(GFP_KERNEL);
-		if (!pages[i])
-			goto out_free;
-	}
+	/*
+	 * There will be some data returned by the server, how much is not
+	 * known yet. Allocate one page and let the XDR layer allocate
+	 * more if needed.
+	 */
+	pages[0] = alloc_page(GFP_KERNEL);
 
 	/* for decoding across pages */
 	res.acl_scratch = alloc_page(GFP_KERNEL);
 	if (!res.acl_scratch)
 		goto out_free;
 
-	args.acl_len = npages * PAGE_SIZE;
+	args.acl_len = ARRAY_SIZE(pages) << PAGE_SHIFT;
 	args.acl_pgbase = 0;
 
-	dprintk("%s  buf %p buflen %zu npages %d args.acl_len %zu\n",
-		__func__, buf, buflen, npages, args.acl_len);
+	dprintk("%s  buf %p buflen %zu args.acl_len %zu\n",
+		__func__, buf, buflen, args.acl_len);
 	ret = nfs4_call_sync(NFS_SERVER(inode)->client, NFS_SERVER(inode),
 			     &msg, &args.seq_args, &res.seq_res, 0);
 	if (ret)
@@ -4503,7 +4493,7 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 out_ok:
 	ret = res.acl_len;
 out_free:
-	for (i = 0; i < npages; i++)
+	for (i = 0; i < ARRAY_SIZE(pages) && pages[i]; i++)
 		if (pages[i])
 			__free_page(pages[i]);
 	if (res.acl_scratch)
diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 5be2868..4e2e2da 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -5207,8 +5207,6 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
 	if ((status = decode_op_hdr(xdr, OP_GETATTR)) != 0)
 		goto out;
 
-	xdr_enter_page(xdr, xdr->buf->page_len);
-
 	/* Calculate the offset of the page data */
 	pg_offset = xdr->buf->head[0].iov_len;
 
-- 
1.8.3.1 (Apple Git-46)