NFSD: Fix checksum mismatches in the duplicate reply cache

nfsd_cache_csum() currently assumes that the server's RPC layer has
been advancing rq_arg.head[0].iov_base as it decodes an incoming
request, because that's the way it used to work. On entry, it
expects that buf->head[0].iov_base points to the start of the NFS
header, and excludes the already-decoded RPC header.

These days however, head[0].iov_base now points to the start of the
RPC header during all processing. It no longer points at the NFS
Call header when execution arrives at nfsd_cache_csum().

In a retransmitted RPC the XID and the NFS header are supposed to
be the same as the original message, but the contents of the
retransmitted RPC header can be different. For example, for krb5,
the GSS sequence number will be different between the two. Thus if
the RPC header is always included in the DRC checksum computation,
the checksum of the retransmitted message might not match the
checksum of the original message, even though the NFS part of these
messages is identical.

The result is that, even if a matching XID is found in the DRC,
the checksum mismatch causes the server to execute the
retransmitted RPC transaction again.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b4e4e04f9931..fe61d9bbcc1f 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -981,6 +981,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
 	const struct svc_procedure *proc = rqstp->rq_procinfo;
 	__be32 *statp = rqstp->rq_accept_statp;
 	struct nfsd_cacherep *rp;
+	unsigned int start, len;
 	__be32 *nfs_reply;
 
 	/*
@@ -989,6 +990,13 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
 	 */
 	rqstp->rq_cachetype = proc->pc_cachetype;
 
+	/*
+	 * ->pc_decode advances the argument stream past the NFS
+	 * Call header, so grab the header's starting location and
+	 * size now for the call to nfsd_cache_lookup().
+	 */
+	start = xdr_stream_pos(&rqstp->rq_arg_stream);
+	len = xdr_stream_remaining(&rqstp->rq_arg_stream);
 	if (!proc->pc_decode(rqstp, &rqstp->rq_arg_stream))
 		goto out_decode_err;
 
@@ -1002,7 +1010,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
 	smp_store_release(&rqstp->rq_status_counter, rqstp->rq_status_counter | 1);
 
 	rp = NULL;
-	switch (nfsd_cache_lookup(rqstp, &rp)) {
+	switch (nfsd_cache_lookup(rqstp, start, len, &rp)) {
 	case RC_DOIT:
 		break;
 	case RC_REPLY: