The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6a2f774424bfdcc2df3e17de0cefe74a4269cad5 Mon Sep 17 00:00:00 2001 From: Chuck Lever chuck.lever@oracle.com Date: Tue, 21 Dec 2021 11:52:06 -0500 Subject: [PATCH] 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 4418517f6f12..2c681785186f 100644 --- 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 eea5b59b6a6c..1743ed04197e 100644 --- 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; }