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Subject: [PATCH v1] NFSD: Fix handling of oversized NFSv4 COMPOUND requests
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org
Cc:     bfields@fieldses.org
Date:   Mon, 05 Sep 2022 15:33:32 -0400
Message-ID: <166240641266.2834.1862985890566562958.stgit@bazille.1015granger.net>
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If an NFS server returns NFS4ERR_RESOURCE on the first operation in
an NFSv4 COMPOUND, there's no way for a client to know where the
problem is and then simplify the compound to make forward progress.

So instead, make NFSD process as many operations in an oversized
COMPOUND as it can and then return NFS4ERR_RESOURCE on the first
operation it did not process.

pynfs NFSv4.0 COMP6 exercises this case, but checks only for the
COMPOUND status code, not whether the server has processed any
of the operations.

pynfs NFSv4.1 SEQ6 and SEQ7 exercise the NFSv4.1 case, which detects
too many operations per COMPOUND by checking against the limits
negotiated when the session was created.

Suggested-by: Bruce Fields <bfields@fieldses.org>
Fixes: 0078117c6d91 ("nfsd: return RESOURCE not GARBAGE_ARGS on too many ops")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4proc.c |   19 +++++++++++++------
 fs/nfsd/nfs4xdr.c  |   12 +++---------
 fs/nfsd/xdr4.h     |    3 ++-
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 7055e1c91d0e..6ef0795fefb4 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -2631,9 +2631,6 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 	status = nfserr_minor_vers_mismatch;
 	if (nfsd_minorversion(nn, args->minorversion, NFSD_TEST) <= 0)
 		goto out;
-	status = nfserr_resource;
-	if (args->opcnt > NFSD_MAX_OPS_PER_COMPOUND)
-		goto out;
 
 	status = nfs41_check_op_ordering(args);
 	if (status) {
@@ -2646,10 +2643,20 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 
 	rqstp->rq_lease_breaker = (void **)&cstate->clp;
 
-	trace_nfsd_compound(rqstp, args->opcnt);
+	trace_nfsd_compound(rqstp, args->client_opcnt);
 	while (!status && resp->opcnt < args->opcnt) {
 		op = &args->ops[resp->opcnt++];
 
+		if (unlikely(resp->opcnt == NFSD_MAX_OPS_PER_COMPOUND)) {
+			/* If there are still more operations to process,
+			 * stop here and report NFS4ERR_RESOURCE. */
+			if (cstate->minorversion == 0 &&
+			    args->client_opcnt > resp->opcnt) {
+				op->status = nfserr_resource;
+				goto encode_op;
+			}
+		}
+
 		/*
 		 * The XDR decode routines may have pre-set op->status;
 		 * for example, if there is a miscellaneous XDR error
@@ -2725,8 +2732,8 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 			status = op->status;
 		}
 
-		trace_nfsd_compound_status(args->opcnt, resp->opcnt, status,
-					   nfsd4_op_name(op->opnum));
+		trace_nfsd_compound_status(args->client_opcnt, resp->opcnt,
+					   status, nfsd4_op_name(op->opnum));
 
 		nfsd4_cstate_clear_replay(cstate);
 		nfsd4_increment_op_stats(op->opnum);
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 4b69e86240eb..09519b4a860a 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2359,16 +2359,10 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp)
 
 	if (xdr_stream_decode_u32(argp->xdr, &argp->minorversion) < 0)
 		return false;
-	if (xdr_stream_decode_u32(argp->xdr, &argp->opcnt) < 0)
+	if (xdr_stream_decode_u32(argp->xdr, &argp->client_opcnt) < 0)
 		return false;
-
-	/*
-	 * NFS4ERR_RESOURCE is a more helpful error than GARBAGE_ARGS
-	 * here, so we return success at the xdr level so that
-	 * nfsd4_proc can handle this is an NFS-level error.
-	 */
-	if (argp->opcnt > NFSD_MAX_OPS_PER_COMPOUND)
-		return true;
+	argp->opcnt = min_t(u32, argp->client_opcnt,
+			    NFSD_MAX_OPS_PER_COMPOUND);
 
 	if (argp->opcnt > ARRAY_SIZE(argp->iops)) {
 		argp->ops = vcalloc(argp->opcnt, sizeof(*argp->ops));
diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index 96267258e629..466e2786fc97 100644
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -717,9 +717,10 @@ struct nfsd4_compoundargs {
 	struct svcxdr_tmpbuf		*to_free;
 	struct svc_rqst			*rqstp;
 
-	u32				taglen;
 	char *				tag;
+	u32				taglen;
 	u32				minorversion;
+	u32				client_opcnt;
 	u32				opcnt;
 	struct nfsd4_op			*ops;
 	struct nfsd4_op			iops[8];