From daa52e37851a5a1b5890e7a250a27e94a8b9f273 Mon Sep 17 00:00:00 2001
From: Chuck Lever <cel@kernel.org>
Date: Sun, 12 Jul 2026 15:31:22 -0400
Subject: [PATCH] xdrgen: Fix opaque and string encoders for unbounded members

The variable-length opaque and string encoder templates emit an
unconditional bound check, "if (value->NAME.len > MAXSIZE) return
false". XDR represents an unbounded specifier (opaque foo<>, string
foo<>) as a maxsize of 0, so for an unbounded member the check
degenerates to "len > 0" and the generated encoder refuses every
non-empty value.

The decoder does not share this defect. It delegates to
xdrgen_decode_opaque() and xdrgen_decode_string(), which treat a
maxlen of 0 as unbounded and skip the length check. The sibling
variable-length array templates already guard their bound check
with maxsize != "0".

Guard the bound check the same way in each affected template -- the
struct and pointer forms of both the opaque and string encoders --
so an unbounded member encodes a payload of any length while a
bounded member keeps its limit.

An explicit zero-length bound (foo<0>) parses to the same maxsize of
0 and so also skips the check; xdrgen does not distinguish it from
the unbounded form, matching the decoder and the array encoders.

Fixes: 4b132aacb076 ("tools: Add xdrgen")
Link: https://patch.msgid.link/20260712193122.116845-6-cel@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/string.j2   | 2 ++
 .../templates/C/pointer/encoder/variable_length_opaque.j2       | 2 ++
 tools/net/sunrpc/xdrgen/templates/C/struct/encoder/string.j2    | 2 ++
 .../xdrgen/templates/C/struct/encoder/variable_length_opaque.j2 | 2 ++
 4 files changed, 8 insertions(+)

diff --git a/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/string.j2 b/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/string.j2
index cf65b71eaef3..7ddc2bf3edac 100644
--- a/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/string.j2
+++ b/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/string.j2
@@ -2,7 +2,9 @@
 {% if annotate %}
 	/* member {{ name }} (variable-length string) */
 {% endif %}
+{% if maxsize != "0" %}
 	if (value->{{ name }}.len > {{ maxsize }})
 		return false;
+{% endif %}
 	if (xdr_stream_encode_opaque(xdr, value->{{ name }}.data, value->{{ name }}.len) < 0)
 		return false;
diff --git a/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/variable_length_opaque.j2 b/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/variable_length_opaque.j2
index 1d477c2d197a..5bf00070ae95 100644
--- a/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/variable_length_opaque.j2
+++ b/tools/net/sunrpc/xdrgen/templates/C/pointer/encoder/variable_length_opaque.j2
@@ -2,7 +2,9 @@
 {% if annotate %}
 	/* member {{ name }} (variable-length opaque) */
 {% endif %}
+{% if maxsize != "0" %}
 	if (value->{{ name }}.len > {{ maxsize }})
 		return false;
+{% endif %}
 	if (xdr_stream_encode_opaque(xdr, value->{{ name }}.data, value->{{ name }}.len) < 0)
 		return false;
diff --git a/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/string.j2 b/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/string.j2
index cf65b71eaef3..7ddc2bf3edac 100644
--- a/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/string.j2
+++ b/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/string.j2
@@ -2,7 +2,9 @@
 {% if annotate %}
 	/* member {{ name }} (variable-length string) */
 {% endif %}
+{% if maxsize != "0" %}
 	if (value->{{ name }}.len > {{ maxsize }})
 		return false;
+{% endif %}
 	if (xdr_stream_encode_opaque(xdr, value->{{ name }}.data, value->{{ name }}.len) < 0)
 		return false;
diff --git a/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/variable_length_opaque.j2 b/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/variable_length_opaque.j2
index 1d477c2d197a..5bf00070ae95 100644
--- a/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/variable_length_opaque.j2
+++ b/tools/net/sunrpc/xdrgen/templates/C/struct/encoder/variable_length_opaque.j2
@@ -2,7 +2,9 @@
 {% if annotate %}
 	/* member {{ name }} (variable-length opaque) */
 {% endif %}
+{% if maxsize != "0" %}
 	if (value->{{ name }}.len > {{ maxsize }})
 		return false;
+{% endif %}
 	if (xdr_stream_encode_opaque(xdr, value->{{ name }}.data, value->{{ name }}.len) < 0)
 		return false;