linux-kernel - [PATCH 3/5] rslib: Fix wrong result if gffunc(0) != 1

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240924123141.16962-4-zhangboyang.id@gmail.com>
Date: Tue, 24 Sep 2024 20:31:39 +0800
From: Zhang Boyang <zhangboyang.id@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ferdinand Blomqvist <ferdinand.blomqvist@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Zhang Boyang <zhangboyang.id@...il.com>
Subject: [PATCH 3/5] rslib: Fix wrong result if gffunc(0) != 1

The rslib allows customizing the finite field by the `gffunc' parameter
of init_rs_non_canonical(). However, there are several places in rslib
use hard-coded 1, leading to errors if gffunc(0) != 1. This patch
replaces hard-coded 1 with alpha_to[0] to fix this problem. One of such
`gffunc' might be gffunc'(x) = swab16(gffunc(swab16(x))), as
gffunc'(0) = swab16(1). This special gffunc'(x) is useful when
implementing RS coder for 16 bit foreign-endian symbols.

Fixes: d7e5a5462f68 ("[RSLIB] Support non-canonical GF representations")
Signed-off-by: Zhang Boyang <zhangboyang.id@...il.com>
---
 lib/reed_solomon/decode_rs.c    | 4 ++--
 lib/reed_solomon/reed_solomon.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
index 805de84ae83d..6c1d53d1b702 100644
--- a/lib/reed_solomon/decode_rs.c
+++ b/lib/reed_solomon/decode_rs.c
@@ -104,7 +104,7 @@
 
  decode:
 	memset(&lambda[1], 0, nroots * sizeof(lambda[0]));
-	lambda[0] = 1;
+	lambda[0] = alpha_to[0];
 
 	if (no_eras > 0) {
 		/* Init lambda to be the erasure locator polynomial */
@@ -198,7 +198,7 @@
 	memcpy(&reg[1], &lambda[1], nroots * sizeof(reg[0]));
 	count = 0;		/* Number of roots of lambda(x) */
 	for (i = 1, k = iprim - 1; i <= nn; i++, k = rs_modnn(rs, k + iprim)) {
-		q = 1;		/* lambda[0] is always 0 */
+		q = alpha_to[0];	/* lambda[0] is always 0 */
 		for (j = deg_lambda; j > 0; j--) {
 			if (reg[j] != nn) {
 				reg[j] = rs_modnn(rs, reg[j] + j);
diff --git a/lib/reed_solomon/reed_solomon.c b/lib/reed_solomon/reed_solomon.c
index bbc01bad3053..bb4f44c8edba 100644
--- a/lib/reed_solomon/reed_solomon.c
+++ b/lib/reed_solomon/reed_solomon.c
@@ -131,9 +131,9 @@ static struct rs_codec *codec_init(int symsize, int gfpoly, int (*gffunc)(int),
 	rs->iprim = iprim / prim;
 
 	/* Form RS code generator polynomial from its roots */
-	rs->genpoly[0] = 1;
+	rs->genpoly[0] = rs->alpha_to[0];
 	for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
-		rs->genpoly[i + 1] = 1;
+		rs->genpoly[i + 1] = rs->alpha_to[0];
 		/* Multiply rs->genpoly[] by  @**(root + x) */
 		for (j = i; j > 0; j--) {
 			if (rs->genpoly[j] != 0) {
-- 
2.30.2