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Subject[PATCH 5.15 044/262] NFSD: Fix zero-length NFSv3 WRITEs
Date
From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit 6a2f774424bfdcc2df3e17de0cefe74a4269cad5 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfsd/nfs3proc.c | 6 +-----
fs/nfsd/nfsproc.c | 5 -----
2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 354bbfcd96aae..b540489ea240d 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -211,15 +211,11 @@ 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 de282f3273c50..312fd289be583 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;
}

--
2.34.1


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