NFS: advance nfs_entry cookie only after decoding completes successfully

In nfs[34]_decode_dirent, the cookie is advanced as soon as it is
read, but decoding may still fail later in the function, returning
an error.  Because the cookie has been advanced, the failing entry
is not re-requested from the server, resulting in a missing directory
entry.

In addition, nfs v3 and v4 read the cookie at different locations
in the xdr_stream, so the behavior of the two can be inconsistent.

Fix these by reading the cookie into a temporary variable, and
only advancing the cookie once the entire entry has been decoded
from the xdr_stream successfully.
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs3xdr.c

@@ -1997,6 +1997,7 @@ int nfs3_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	struct nfs_entry old = *entry;
 	__be32 *p;
 	int error;
+	u64 new_cookie;
 
 	p = xdr_inline_decode(xdr, 4);
 	if (unlikely(p == NULL))
@@ -2019,8 +2020,7 @@ int nfs3_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	if (unlikely(error))
 		return error;
 
-	entry->prev_cookie = entry->cookie;
-	error = decode_cookie3(xdr, &entry->cookie);
+	error = decode_cookie3(xdr, &new_cookie);
 	if (unlikely(error))
 		return error;
 
@@ -2054,6 +2054,9 @@ int nfs3_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 			zero_nfs_fh3(entry->fh);
 	}
 
+	entry->prev_cookie = entry->cookie;
+	entry->cookie = new_cookie;
+
 	return 0;
 
 out_overflow:

fs/nfs/nfs4xdr.c

@@ -7518,6 +7518,7 @@ int nfs4_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	unsigned int savep;
 	uint32_t bitmap[3] = {0};
 	uint32_t len;
+	uint64_t new_cookie;
 	__be32 *p = xdr_inline_decode(xdr, 4);
 	if (unlikely(!p))
 		goto out_overflow;
@@ -7534,8 +7535,7 @@ int nfs4_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	p = xdr_inline_decode(xdr, 12);
 	if (unlikely(!p))
 		goto out_overflow;
-	entry->prev_cookie = entry->cookie;
-	p = xdr_decode_hyper(p, &entry->cookie);
+	p = xdr_decode_hyper(p, &new_cookie);
 	entry->len = be32_to_cpup(p);
 
 	p = xdr_inline_decode(xdr, entry->len);
@@ -7569,6 +7569,9 @@ int nfs4_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	if (entry->fattr->valid & NFS_ATTR_FATTR_TYPE)
 		entry->d_type = nfs_umode_to_dtype(entry->fattr->mode);
 
+	entry->prev_cookie = entry->cookie;
+	entry->cookie = new_cookie;
+
 	return 0;
 
 out_overflow: