This was the original commit:
commit 71c02863246167b3d1639b8278681ca8ebedcb4e
Author: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Date: Thu Aug 19 20:34:59 2021 +1000
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@xxxxxxxxxx>
On Sun, Sep 7, 2025 at 12:59 PM Steve French <smfrench@xxxxxxxxx> wrote:
>
> Ronnie may have additional context, but it may have been forked due to
> unrelated restrictions on the arc4 module (that had nothing to do with
> cifs.ko very narrow usage of arc4) breaking cifs.ko.
>
> Ronnie,
> Do you remember the context?
>
> On Sat, Sep 6, 2025 at 10:22 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> >
> > fs/smb/common/cifs_arc4.c has an implementation of ARC4, but a copy of
> > this same code is also present in lib/crypto/arc4.c to serve the other
> > users of this legacy algorithm in the kernel. Remove the duplicate
> > implementation in fs/smb/, which seems to have been added because of a
> > misunderstanding, and just use the lib/crypto/ one.
> >
> > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> > ---
> > fs/smb/client/Kconfig | 1 +
> > fs/smb/client/cifsencrypt.c | 8 ++--
> > fs/smb/common/Makefile | 1 -
> > fs/smb/common/arc4.h | 23 ------------
> > fs/smb/common/cifs_arc4.c | 75 -------------------------------------
> > fs/smb/server/Kconfig | 1 +
> > fs/smb/server/auth.c | 9 ++---
> > 7 files changed, 10 insertions(+), 108 deletions(-)
> > delete mode 100644 fs/smb/common/arc4.h
> > delete mode 100644 fs/smb/common/cifs_arc4.c
> >
> > diff --git a/fs/smb/client/Kconfig b/fs/smb/client/Kconfig
> > index 9f05f94e265a6..a4c02199fef48 100644
> > --- a/fs/smb/client/Kconfig
> > +++ b/fs/smb/client/Kconfig
> > @@ -13,10 +13,11 @@ config CIFS
> > select CRYPTO_AEAD2
> > select CRYPTO_CCM
> > select CRYPTO_GCM
> > select CRYPTO_ECB
> > select CRYPTO_AES
> > + select CRYPTO_LIB_ARC4
> > select KEYS
> > select DNS_RESOLVER
> > select ASN1
> > select OID_REGISTRY
> > select NETFS_SUPPORT
> > diff --git a/fs/smb/client/cifsencrypt.c b/fs/smb/client/cifsencrypt.c
> > index 3cc6862469087..7b7c8c38fdd08 100644
> > --- a/fs/smb/client/cifsencrypt.c
> > +++ b/fs/smb/client/cifsencrypt.c
> > @@ -20,12 +20,12 @@
> > #include <linux/ctype.h>
> > #include <linux/random.h>
> > #include <linux/highmem.h>
> > #include <linux/fips.h>
> > #include <linux/iov_iter.h>
> > -#include "../common/arc4.h"
> > #include <crypto/aead.h>
> > +#include <crypto/arc4.h>
> >
> > static size_t cifs_shash_step(void *iter_base, size_t progress, size_t len,
> > void *priv, void *priv2)
> > {
> > struct shash_desc *shash = priv;
> > @@ -723,13 +723,13 @@ calc_seckey(struct cifs_ses *ses)
> > if (!ctx_arc4) {
> > cifs_dbg(VFS, "Could not allocate arc4 context\n");
> > return -ENOMEM;
> > }
> >
> > - 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);
> > + arc4_setkey(ctx_arc4, ses->auth_key.response, CIFS_SESS_KEY_SIZE);
> > + 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);
> > /* and make len as that of session key only */
> > ses->auth_key.len = CIFS_SESS_KEY_SIZE;
> > diff --git a/fs/smb/common/Makefile b/fs/smb/common/Makefile
> > index c66dbbc1469c3..9e0730a385fb1 100644
> > --- a/fs/smb/common/Makefile
> > +++ b/fs/smb/common/Makefile
> > @@ -1,7 +1,6 @@
> > # SPDX-License-Identifier: GPL-2.0-only
> > #
> > # Makefile for Linux filesystem routines that are shared by client and server.
> > #
> >
> > -obj-$(CONFIG_SMBFS) += cifs_arc4.o
> > obj-$(CONFIG_SMBFS) += cifs_md4.o
> > diff --git a/fs/smb/common/arc4.h b/fs/smb/common/arc4.h
> > deleted file mode 100644
> > index 12e71ec033a18..0000000000000
> > --- a/fs/smb/common/arc4.h
> > +++ /dev/null
> > @@ -1,23 +0,0 @@
> > -/* 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 */
> > diff --git a/fs/smb/common/cifs_arc4.c b/fs/smb/common/cifs_arc4.c
> > deleted file mode 100644
> > index df360ca47826a..0000000000000
> > --- a/fs/smb/common/cifs_arc4.c
> > +++ /dev/null
> > @@ -1,75 +0,0 @@
> > -// SPDX-License-Identifier: GPL-2.0-or-later
> > -/*
> > - * Cryptographic API
> > - *
> > - * ARC4 Cipher Algorithm
> > - *
> > - * Jon Oberheide <jon@xxxxxxxxxxxxx>
> > - */
> > -
> > -#include <linux/module.h>
> > -#include "arc4.h"
> > -
> > -MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
> > -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);
> > diff --git a/fs/smb/server/Kconfig b/fs/smb/server/Kconfig
> > index 4a23a5e7e8fec..098cac98d31e6 100644
> > --- a/fs/smb/server/Kconfig
> > +++ b/fs/smb/server/Kconfig
> > @@ -8,10 +8,11 @@ config SMB_SERVER
> > select NLS_UCS2_UTILS
> > select CRYPTO
> > select CRYPTO_MD5
> > select CRYPTO_HMAC
> > select CRYPTO_ECB
> > + select CRYPTO_LIB_ARC4
> > select CRYPTO_LIB_DES
> > select CRYPTO_LIB_SHA256
> > select CRYPTO_SHA256
> > select CRYPTO_CMAC
> > select CRYPTO_SHA512
> > diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
> > index d99871c214518..b4020bb55a268 100644
> > --- a/fs/smb/server/auth.c
> > +++ b/fs/smb/server/auth.c
> > @@ -18,20 +18,20 @@
> >
> > #include "auth.h"
> > #include "glob.h"
> >
> > #include <linux/fips.h>
> > +#include <crypto/arc4.h>
> > #include <crypto/des.h>
> >
> > #include "server.h"
> > #include "smb_common.h"
> > #include "connection.h"
> > #include "mgmt/user_session.h"
> > #include "mgmt/user_config.h"
> > #include "crypto_ctx.h"
> > #include "transport_ipc.h"
> > -#include "../common/arc4.h"
> >
> > /*
> > * Fixed format data defining GSS header and fixed string
> > * "not_defined_in_RFC4178@please_ignore".
> > * So sec blob data in neg phase could be generated statically.
> > @@ -363,14 +363,13 @@ int ksmbd_decode_ntlmssp_auth_blob(struct authenticate_message *authblob,
> >
> > ctx_arc4 = kmalloc(sizeof(*ctx_arc4), KSMBD_DEFAULT_GFP);
> > if (!ctx_arc4)
> > return -ENOMEM;
> >
> > - cifs_arc4_setkey(ctx_arc4, sess->sess_key,
> > - SMB2_NTLMV2_SESSKEY_SIZE);
> > - cifs_arc4_crypt(ctx_arc4, sess->sess_key,
> > - (char *)authblob + sess_key_off, sess_key_len);
> > + arc4_setkey(ctx_arc4, sess->sess_key, SMB2_NTLMV2_SESSKEY_SIZE);
> > + arc4_crypt(ctx_arc4, sess->sess_key,
> > + (char *)authblob + sess_key_off, sess_key_len);
> > kfree_sensitive(ctx_arc4);
> > }
> >
> > return ret;
> > }
> >
> > base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
> > --
> > 2.50.1
> >
> >
>
>
> --
> Thanks,
>
> Steve
--
Thanks,
Steve
