NFS: clean up short packet handling for NFSv2 readdir

Currently, the NFS readdir decoders have a workaround for buggy servers
that send an empty readdir response with the EOF bit unset. If the
server sends a malformed response in some cases, this workaround kicks
in and just returns an empty response rather than returning a proper
error to the caller.

This patch does 3 things:

1) have malformed responses with no entries return error (-EIO)

2) preserve existing workaround for servers that send empty
   responses with the EOF marker unset.

3) Add some comments to clarify the logic in nfs_xdr_readdirres().

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 28 insertions, 9 deletions

diff --git a/fs/nfs/nfs2xdr.c b/fs/nfs/nfs2xdr.c
index 1f7ea675e0c5..86a80b33ec82 100644
--- a/fs/nfs/nfs2xdr.c
+++ b/fs/nfs/nfs2xdr.c
@@ -428,7 +428,7 @@ nfs_xdr_readdirres(struct rpc_rqst *req, __be32 *p, void *dummy)
         size_t hdrlen;
         unsigned int pglen, recvd;
         u32 len;
-        int status, nr;
+        int status, nr = 0;
         __be32 *end, *entry, *kaddr;
 
         if ((status = ntohl(*p++)))
@@ -452,7 +452,12 @@ nfs_xdr_readdirres(struct rpc_rqst *req, __be32 *p, void *dummy)
         kaddr = p = kmap_atomic(*page, KM_USER0);
         end = (__be32 *)((char *)p + pglen);
         entry = p;
-        for (nr = 0; *p++; nr++) {
+
+        /* Make sure the packet actually has a value_follows and EOF entry */
+        if ((entry + 1) > end)
+                goto short_pkt;
+
+        for (; *p++; nr++) {
                 if (p + 2 > end)
                         goto short_pkt;
                 p++; /* fileid */
@@ -467,18 +472,32 @@ nfs_xdr_readdirres(struct rpc_rqst *req, __be32 *p, void *dummy)
                         goto short_pkt;
                 entry = p;
         }
-        if (!nr && (entry[0] != 0 || entry[1] == 0))
-                goto short_pkt;
+
+        /*
+         * Apparently some server sends responses that are a valid size, but
+         * contain no entries, and have value_follows==0 and EOF==0. For
+         * those, just set the EOF marker.
+         */
+        if (!nr && entry[1] == 0) {
+                dprintk("NFS: readdir reply truncated!\n");
+                entry[1] = 1;
+        }
  out:
         kunmap_atomic(kaddr, KM_USER0);
         return nr;
  short_pkt:
+        /*
+         * When we get a short packet there are 2 possibilities. We can
+         * return an error, or fix up the response to look like a valid
+         * response and return what we have so far. If there are no
+         * entries and the packet was short, then return -EIO. If there
+         * are valid entries in the response, return them and pretend that
+         * the call was successful, but incomplete. The caller can retry the
+         * readdir starting at the last cookie.
+         */
         entry[0] = entry[1] = 0;
-        /* truncate listing ? */
-        if (!nr) {
-                dprintk("NFS: readdir reply truncated!\n");
-                entry[1] = 1;
-        }
+        if (!nr)
+                nr = -errno_NFSERR_IO;
         goto out;
 err_unmap:
         nr = -errno_NFSERR_IO;