NFSv4: Fix pointer arithmetic in decode_getacl

Resetting the cursor xdr->p to a previous value is not a safe
practice: if the xdr_stream has crossed out of the initial iovec,
then a bunch of other fields would need to be reset too.

Fix this issue by using xdr_enter_page() so that the buffer gets
page aligned at the bitmap _before_ we decode it.

Also fix the confusion of the ACL length with the page buffer length
by not adding the base offset to the ACL length...
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org

fs/nfs/nfs4proc.c

@@ -3819,7 +3819,7 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 	if (ret)
 		goto out_free;
 
-	acl_len = res.acl_len - res.acl_data_offset;
+	acl_len = res.acl_len;
 	if (acl_len > args.acl_len)
 		nfs4_write_cached_acl(inode, NULL, 0, acl_len);
 	else

fs/nfs/nfs4xdr.c

@@ -5049,18 +5049,14 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
 	uint32_t attrlen,
 		 bitmap[3] = {0};
 	int status;
-	size_t page_len = xdr->buf->page_len;
 
 	res->acl_len = 0;
 	if ((status = decode_op_hdr(xdr, OP_GETATTR)) != 0)
 		goto out;
 
+	xdr_enter_page(xdr, xdr->buf->page_len);
+
 	bm_p = xdr->p;
-	res->acl_data_offset = be32_to_cpup(bm_p) + 2;
-	res->acl_data_offset <<= 2;
-	/* Check if the acl data starts beyond the allocated buffer */
-	if (res->acl_data_offset > page_len)
-		return -ERANGE;
 
 	if ((status = decode_attr_bitmap(xdr, bitmap)) != 0)
 		goto out;
@@ -5074,23 +5070,20 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
 		/* The bitmap (xdr len + bitmaps) and the attr xdr len words
 		 * are stored with the acl data to handle the problem of
 		 * variable length bitmaps.*/
-		xdr->p = bm_p;
+		res->acl_data_offset = (xdr->p - bm_p) << 2;
 
 		/* We ignore &savep and don't do consistency checks on
 		 * the attr length.  Let userspace figure it out.... */
-		attrlen += res->acl_data_offset;
-		if (attrlen > page_len) {
+		res->acl_len = attrlen;
+		if (attrlen + res->acl_data_offset > xdr->buf->page_len) {
 			if (res->acl_flags & NFS4_ACL_LEN_REQUEST) {
 				/* getxattr interface called with a NULL buf */
-				res->acl_len = attrlen;
 				goto out;
 			}
-			dprintk("NFS: acl reply: attrlen %u > page_len %zu\n",
-					attrlen, page_len);
+			dprintk("NFS: acl reply: attrlen %u > page_len %u\n",
+					attrlen, xdr->buf->page_len);
 			return -EINVAL;
 		}
-		xdr_read_pages(xdr, attrlen);
-		res->acl_len = attrlen;
 	} else
 		status = -EOPNOTSUPP;