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>

diff --git a/fs/nfs/nfs2xdr.c b/fs/nfs/nfs2xdr.c
index 1f7ea675e0c5e9489d8316b60969d159f386d8ab..86a80b33ec82f47b37a8ed23f624f8e0b46a1ecb 100644 (file)
--- 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;