From 34d9ab78568d63d8097911237897b188bdaba9c2 Mon Sep 17 00:00:00 2001
From: Filippo Valsorda <filippo@golang.org>
Date: Thu, 31 Mar 2022 12:31:58 -0400
Subject: [PATCH] crypto/elliptic: tolerate zero-padded scalars in generic
 P-256

Upstream-Status: Backport [https://github.com/golang/go/commit/7139e8b024604ab168b51b99c6e8168257a5bf58]
CVE: CVE-2022-28327
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>


Updates #52075
Fixes #52076
Fixes CVE-2022-28327

Change-Id: I595a7514c9a0aa1b9c76aedfc2307e1124271f27
Reviewed-on: https://go-review.googlesource.com/c/go/+/397136
Trust: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>
---
 src/crypto/elliptic/p256.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/crypto/elliptic/p256.go b/src/crypto/elliptic/p256.go
index c23e414..787e3e7 100644
--- a/src/crypto/elliptic/p256.go
+++ b/src/crypto/elliptic/p256.go
@@ -51,7 +51,7 @@ func p256GetScalar(out *[32]byte, in []byte) {
 	n := new(big.Int).SetBytes(in)
 	var scalarBytes []byte
 
-	if n.Cmp(p256Params.N) >= 0 {
+	if n.Cmp(p256Params.N) >= 0 || len(in) > len(out) {
 		n.Mod(n, p256Params.N)
 		scalarBytes = n.Bytes()
 	} else {