NFSD: Fix zero-length NFSv3 WRITEs

The Linux NFS server currently responds to a zero-length NFSv3 WRITE
request with NFS3ERR_IO. It responds to a zero-length NFSv4 WRITE
with NFS4_OK and count of zero.

RFC 1813 says of the WRITE procedure's @count argument:

count
         The number of bytes of data to be written. If count is
         0, the WRITE will succeed and return a count of 0,
         barring errors due to permissions checking.

RFC 8881 has similar language for NFSv4, though NFSv4 removed the
explicit @count argument because that value is already contained in
the opaque payload array.

The synthetic client pynfs's WRT4 and WRT15 tests do emit zero-
length WRITEs to exercise this spec requirement. Commit fdec6114ee1f
("nfsd4: zero-length WRITE should succeed") addressed the same
problem there with the same fix.

But interestingly the Linux NFS client does not appear to emit zero-
length WRITEs, instead squelching them. I'm not aware of a test that
can generate such WRITEs for NFSv3, so I wrote a naive C program to
generate a zero-length WRITE and test this fix.

Fixes: 8154ef2776aa ("NFSD: Clean up legacy NFS WRITE argument XDR decoders")
Reported-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 4418517..2c68178 100644 (file)
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -202,15 +202,11 @@ nfsd3_proc_write(struct svc_rqst *rqstp)
        fh_copy(&resp->fh, &argp->fh);
        resp->committed = argp->stable;
        nvecs = svc_fill_write_vector(rqstp, &argp->payload);
-       if (!nvecs) {
-               resp->status = nfserr_io;
-               goto out;
-       }
+
        resp->status = nfsd_write(rqstp, &resp->fh, argp->offset,
                                  rqstp->rq_vec, nvecs, &cnt,
                                  resp->committed, resp->verf);
        resp->count = cnt;
-out:
        return rpc_success;
 }
 

diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index eea5b59..1743ed0 100644 (file)
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -235,10 +235,6 @@ nfsd_proc_write(struct svc_rqst *rqstp)
                argp->len, argp->offset);
 
        nvecs = svc_fill_write_vector(rqstp, &argp->payload);
-       if (!nvecs) {
-               resp->status = nfserr_io;
-               goto out;
-       }
 
        resp->status = nfsd_write(rqstp, fh_copy(&resp->fh, &argp->fh),
                                  argp->offset, rqstp->rq_vec, nvecs,
@@ -247,7 +243,6 @@ nfsd_proc_write(struct svc_rqst *rqstp)
                resp->status = fh_getattr(&resp->fh, &resp->stat);
        else if (resp->status == nfserr_jukebox)
                return rpc_drop_reply;
-out:
        return rpc_success;
 }