cifs: fork arc4 and create a separate module for it for cifs and other users

We can not drop ARC4 and basically destroy CIFS connectivity for
almost all CIFS users so create a new forked ARC4 module that CIFS and other
subsystems that have a hard dependency on ARC4 can use.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/Kconfig

@@ -358,7 +358,14 @@ config NFS_V4_2_SSC_HELPER
 
 source "net/sunrpc/Kconfig"
 source "fs/ceph/Kconfig"
+
 source "fs/cifs/Kconfig"
+
+config CIFS_COMMON
+	tristate
+	default y if CIFS=y
+	default m if CIFS=m
+
 source "fs/coda/Kconfig"
 source "fs/afs/Kconfig"
 source "fs/9p/Kconfig"

fs/Makefile

@@ -96,6 +96,7 @@ obj-$(CONFIG_LOCKD)		+= lockd/
 obj-$(CONFIG_NLS)		+= nls/
 obj-$(CONFIG_UNICODE)		+= unicode/
 obj-$(CONFIG_SYSV_FS)		+= sysv/
+obj-$(CONFIG_CIFS_COMMON)	+= cifs_common/
 obj-$(CONFIG_CIFS)		+= cifs/
 obj-$(CONFIG_HPFS_FS)		+= hpfs/
 obj-$(CONFIG_NTFS_FS)		+= ntfs/

fs/cifs/Kconfig

@@ -10,7 +10,6 @@ config CIFS
 	select CRYPTO_SHA512
 	select CRYPTO_CMAC
 	select CRYPTO_HMAC
-	select CRYPTO_LIB_ARC4
 	select CRYPTO_AEAD2
 	select CRYPTO_CCM
 	select CRYPTO_GCM

fs/cifs/cifsencrypt.c

@@ -22,7 +22,7 @@
 #include <linux/random.h>
 #include <linux/highmem.h>
 #include <linux/fips.h>
-#include <crypto/arc4.h>
+#include "../cifs_common/arc4.h"
 #include <crypto/aead.h>
 
 int __cifs_calc_signature(struct smb_rqst *rqst,
@@ -699,9 +699,9 @@ calc_seckey(struct cifs_ses *ses)
 		return -ENOMEM;
 	}
 
-	arc4_setkey(ctx_arc4, ses->auth_key.response, CIFS_SESS_KEY_SIZE);
-	arc4_crypt(ctx_arc4, ses->ntlmssp->ciphertext, sec_key,
-		   CIFS_CPHTXT_SIZE);
+	cifs_arc4_setkey(ctx_arc4, ses->auth_key.response, CIFS_SESS_KEY_SIZE);
+	cifs_arc4_crypt(ctx_arc4, ses->ntlmssp->ciphertext, sec_key,
+			CIFS_CPHTXT_SIZE);
 
 	/* make secondary_key/nonce as session key */
 	memcpy(ses->auth_key.response, sec_key, CIFS_SESS_KEY_SIZE);

fs/cifs_common/Makefile

+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for Linux filesystem routines that are shared by client and server.
+#
+
+obj-$(CONFIG_CIFS_COMMON) += cifs_arc4.o

fs/cifs_common/arc4.h

+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Common values for ARC4 Cipher Algorithm
+ */
+
+#ifndef _CRYPTO_ARC4_H
+#define _CRYPTO_ARC4_H
+
+#include <linux/types.h>
+
+#define ARC4_MIN_KEY_SIZE	1
+#define ARC4_MAX_KEY_SIZE	256
+#define ARC4_BLOCK_SIZE		1
+
+struct arc4_ctx {
+	u32 S[256];
+	u32 x, y;
+};
+
+int cifs_arc4_setkey(struct arc4_ctx *ctx, const u8 *in_key, unsigned int key_len);
+void cifs_arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in, unsigned int len);
+
+#endif /* _CRYPTO_ARC4_H */

fs/cifs_common/cifs_arc4.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Cryptographic API
+ *
+ * ARC4 Cipher Algorithm
+ *
+ * Jon Oberheide <jon@oberheide.org>
+ */
+
+#include <linux/module.h>
+#include "arc4.h"
+
+MODULE_LICENSE("GPL");
+
+int cifs_arc4_setkey(struct arc4_ctx *ctx, const u8 *in_key, unsigned int key_len)
+{
+	int i, j = 0, k = 0;
+
+	ctx->x = 1;
+	ctx->y = 0;
+
+	for (i = 0; i < 256; i++)
+		ctx->S[i] = i;
+
+	for (i = 0; i < 256; i++) {
+		u32 a = ctx->S[i];
+
+		j = (j + in_key[k] + a) & 0xff;
+		ctx->S[i] = ctx->S[j];
+		ctx->S[j] = a;
+		if (++k >= key_len)
+			k = 0;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(cifs_arc4_setkey);
+
+void cifs_arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in, unsigned int len)
+{
+	u32 *const S = ctx->S;
+	u32 x, y, a, b;
+	u32 ty, ta, tb;
+
+	if (len == 0)
+		return;
+
+	x = ctx->x;
+	y = ctx->y;
+
+	a = S[x];
+	y = (y + a) & 0xff;
+	b = S[y];
+
+	do {
+		S[y] = a;
+		a = (a + b) & 0xff;
+		S[x] = b;
+		x = (x + 1) & 0xff;
+		ta = S[x];
+		ty = (y + ta) & 0xff;
+		tb = S[ty];
+		*out++ = *in++ ^ S[a];
+		if (--len == 0)
+			break;
+		y = ty;
+		a = ta;
+		b = tb;
+	} while (true);
+
+	ctx->x = x;
+	ctx->y = y;
+}
+EXPORT_SYMBOL_GPL(cifs_arc4_crypt);
+
+static int __init
+init_cifs_common(void)
+{
+	return 0;
+}
+static void __init
+exit_cifs_common(void)
+{
+}
+
+module_init(init_cifs_common)
+module_exit(exit_cifs_common)