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crypto: arc4 - mark ecb(arc4) skcipher as obsolete 

Cryptographic algorithms may have a lifespan that is significantly
shorter than Linux's, and so we need to start phasing out algorithms
that are known to be broken, and are no longer fit for general use.

RC4 (or arc4) is a good example here: there are a few areas where its
use is still somewhat acceptable, e.g., for interoperability with legacy
wifi hardware that can only use WEP or TKIP data encryption, but that
should not imply that, for instance, use of RC4 based EAP-TLS by the WPA
supplicant for negotiating TKIP keys is equally acceptable, or that RC4
should remain available as a general purpose cryptographic transform for
all in-kernel and user space clients.

Now that all in-kernel users that need to retain support have moved to
the arc4 library interface, and the known users of ecb(arc4) via the
socket API (iwd [0] and libell [1][2]) have been updated to switch to a
local implementation, we can take the next step, and mark the ecb(arc4)
skcipher as obsolete, and only provide it if the socket API is enabled in
the first place, as well as provide the option to disable all algorithms
that have been marked as obsolete.

[0] https://git.kernel.org/pub/scm/network/wireless/iwd.git/commit/?id=1db8a85a60c64523
[1] https://git.kernel.org/pub/scm/libs/ell/ell.git/commit/?id=53482ce421b727c2
[2] https://git.kernel.org/pub/scm/libs/ell/ell.git/commit/?id=7f6a137809d42f6b

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Ard Biesheuvel 2020-08-31 18:16:49 +03:00 committed by Herbert Xu
parent 274290ed98
commit 9ace677183
2 changed files with 21 additions and 0 deletions
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10
crypto/Kconfig
View File

@ -1199,6 +1199,7 @@ config CRYPTO_ANUBIS
config CRYPTO_ARC4 config CRYPTO_ARC4
tristate "ARC4 cipher algorithm" tristate "ARC4 cipher algorithm"
depends on CRYPTO_USER_API_ENABLE_OBSOLETE
select CRYPTO_SKCIPHER select CRYPTO_SKCIPHER
select CRYPTO_LIB_ARC4 select CRYPTO_LIB_ARC4
help help
@ -1881,6 +1882,15 @@ config CRYPTO_USER_API_AEAD
This option enables the user-spaces interface for AEAD This option enables the user-spaces interface for AEAD
cipher algorithms. cipher algorithms.
config CRYPTO_USER_API_ENABLE_OBSOLETE
bool "Enable obsolete cryptographic algorithms for userspace"
depends on CRYPTO_USER_API
default y
help
Allow obsolete cryptographic algorithms to be selected that have
already been phased out from internal use by the kernel, and are
only useful for userspace clients that still rely on them.
config CRYPTO_STATS config CRYPTO_STATS
bool "Crypto usage statistics for User-space" bool "Crypto usage statistics for User-space"
depends on CRYPTO_USER depends on CRYPTO_USER

11
crypto/arc4.c
View File

@ -11,7 +11,9 @@
#include <crypto/arc4.h> #include <crypto/arc4.h>
#include <crypto/internal/skcipher.h> #include <crypto/internal/skcipher.h>
#include <linux/init.h> #include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/sched.h>
static int crypto_arc4_setkey(struct crypto_skcipher *tfm, const u8 *in_key, static int crypto_arc4_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
unsigned int key_len) unsigned int key_len)
@ -39,6 +41,14 @@ static int crypto_arc4_crypt(struct skcipher_request *req)
return err; return err;
} }
static int crypto_arc4_init(struct crypto_skcipher *tfm)
{
pr_warn_ratelimited("\"%s\" (%ld) uses obsolete ecb(arc4) skcipher\n",
current->comm, (unsigned long)current->pid);
return 0;
}
static struct skcipher_alg arc4_alg = { static struct skcipher_alg arc4_alg = {
/* /*
* For legacy reasons, this is named "ecb(arc4)", not "arc4". * For legacy reasons, this is named "ecb(arc4)", not "arc4".
@ -55,6 +65,7 @@ static struct skcipher_alg arc4_alg = {
.setkey = crypto_arc4_setkey, .setkey = crypto_arc4_setkey,
.encrypt = crypto_arc4_crypt, .encrypt = crypto_arc4_crypt,
.decrypt = crypto_arc4_crypt, .decrypt = crypto_arc4_crypt,
.init = crypto_arc4_init,
}; };
static int __init arc4_init(void) static int __init arc4_init(void)