queue-6.12/xdrgen-initialize-data-pointer-for-zero-length-items.patch

From 223f22b4887ce954ea6ec8d40ee1a88d8283a48d Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Sat, 20 Dec 2025 10:41:09 -0500
Subject: xdrgen: Initialize data pointer for zero-length items

From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit 27b0fcae8f535fb882b1876227a935dcfdf576aa ]

The xdrgen decoders for strings and opaque data had an
optimization that skipped calling xdr_inline_decode() when the
item length was zero. This left the data pointer uninitialized,
which could lead to unpredictable behavior when callers access
it.

Remove the zero-length check and always call xdr_inline_decode().
When passed a length of zero, xdr_inline_decode() returns the
current buffer position, which is valid and matches the behavior
of hand-coded XDR decoders throughout the kernel.

Fixes: 4b132aacb076 ("tools: Add xdrgen")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/sunrpc/xdrgen/_builtins.h | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/include/linux/sunrpc/xdrgen/_builtins.h b/include/linux/sunrpc/xdrgen/_builtins.h
index 66ca3ece951ab..a5ab75d2db044 100644
--- a/include/linux/sunrpc/xdrgen/_builtins.h
+++ b/include/linux/sunrpc/xdrgen/_builtins.h
@@ -188,12 +188,10 @@ xdrgen_decode_string(struct xdr_stream *xdr, string *ptr, u32 maxlen)
 		return false;
 	if (unlikely(maxlen && len > maxlen))
 		return false;
-	if (len != 0) {
-		p = xdr_inline_decode(xdr, len);
-		if (unlikely(!p))
-			return false;
-		ptr->data = (unsigned char *)p;
-	}
+	p = xdr_inline_decode(xdr, len);
+	if (unlikely(!p))
+		return false;
+	ptr->data = (unsigned char *)p;
 	ptr->len = len;
 	return true;
 }
@@ -219,12 +217,10 @@ xdrgen_decode_opaque(struct xdr_stream *xdr, opaque *ptr, u32 maxlen)
 		return false;
 	if (unlikely(maxlen && len > maxlen))
 		return false;
-	if (len != 0) {
-		p = xdr_inline_decode(xdr, len);
-		if (unlikely(!p))
-			return false;
-		ptr->data = (u8 *)p;
-	}
+	p = xdr_inline_decode(xdr, len);
+	if (unlikely(!p))
+		return false;
+	ptr->data = (u8 *)p;
 	ptr->len = len;
 	return true;
 }
-- 
2.51.0