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: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org

1 files changed, 7 insertions, 14 deletions

diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index ca13483edd60..54d3f5a9faa6 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/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;