[PATCH 2/2] nfsd: set op->status when an operation's header cannot be encoded

[Chuck Lever <cel@kernel.org>]

nfsd4_encode_operation() leaves op->status alone when the reply
buffer has no room for the operation's opcode and status word.
nfsd4_proc_compound() reads the unchanged nfs_ok as success and
goes on to the next operation, so the reply counts an operation
whose result was never encoded.

Report the failure through nfsd4_check_resp_size(), which the rest
of the function already uses. It returns NFS4ERR_REP_TOO_BIG, or
NFS4ERR_REP_TOO_BIG_TO_CACHE on a session, and the COMPOUND ends
at that operation.

Two paths narrow the reply buffer: nfsd4_sequence(), which rejects
a SEQUENCE result that does not fit, and nfsd4_encode_splice_read(),
which can leave a single XDR word in the head page. Whether a
COMPOUND reaches that boundary is unproven, so this is a guard
rather than a fix.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfs4xdr.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 7d1b2d6f57f2..a154b02d82b3 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -6723,11 +6723,20 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 	unsigned int op_status_offset;
 	nfsd4_enc encoder;
 
-	if (xdr_stream_encode_u32(xdr, op->opnum) != XDR_UNIT)
+	/*
+	 * nfsd4_proc_compound() stops the COMPOUND early only
+	 * when op->status is set, so a header that cannot be
+	 * encoded has to report the failure here.
+	 */
+	if (xdr_stream_encode_u32(xdr, op->opnum) != XDR_UNIT) {
+		op->status = nfsd4_check_resp_size(resp, XDR_UNIT * 2);
 		goto release;
+	}
 	op_status_offset = xdr->buf->len;
-	if (!xdr_reserve_space(xdr, XDR_UNIT))
+	if (!xdr_reserve_space(xdr, XDR_UNIT)) {
+		op->status = nfsd4_check_resp_size(resp, XDR_UNIT);
 		goto release;
+	}
 
 	if (op->opnum == OP_ILLEGAL)
 		goto status;

-- 
2.54.0