Re: [v2 PATCH] crypto: api - Disallow sha1 in FIPS-mode while allowing hmac(sha1)

[Nicolai Stange <nstange@suse.de>]

Hi Herbert,

many thanks for this, I think this approach can be applied as-is to the
ffdheXYZ(dh) situation. I have some questions/comments inline.

Herbert Xu <herbert@gondor.apana.org.au> writes:

> On Tue, Jan 11, 2022 at 09:34:19PM +1100, Herbert Xu wrote:
>>
>> You're right.  The real issue is that any algorithm with no tests
>> at all is allowed in FIPS mode.  That's clearly suboptimal.  But we
>> can't just ban every unknown algorithm because we rely on that
>> to let things like echainiv through.
>> 
>> Let me figure out a way to differentiate these two cases.
>
> So what I've done is modify hmac so that if the underlying algo
> is FIPS_INTERNAL, then we pre-emptively set FIPS_INTERNAL on the
> hmac side as well.  This can then be cleared if the hmac algorithm
> is explicitly listed as fips_allowed.

I wonder whether this can be made more generic. I.e. would it be possible
to make crypto_grab_spawn() to or in FIPS_INTERNAL into type (iff !(mask
& FIPS_INTERNAL)) and to make crypto_register_instance() to propagate
FIPS_INTERNAL from the template instance's spawns upwards into the
instance's ->cra_flags?


> ---8<---
> Currently we do not distinguish between algorithms that fail on
> the self-test vs. those which are disabled in FIPS mode (not allowed).
> Both are marked as having failed the self-test.
>
> As it has been requested that we need to disable sha1 in FIPS
> mode while still allowing hmac(sha1) this approach needs to change.

On an unrelated note, this will break trusted_key_tpm_ops->init() in
FIPS mode, because trusted_shash_alloc() would fail to get a hold of
sha1. AFAICT, this could potentially make the init_trusted() module_init
to fail, and, as encrypted-keys.ko imports key_type_trusted, prevent the
loading of that one as well. Not sure that's desired...


> This patch allows this scenario by adding a new flag FIPS_INTERNAL
> to indicate those algorithms that have passed the self-test and are
> not FIPS-allowed.  They can then be used for the self-testing of
> other algorithms or by those that are explicitly allowed to use them
> (currently just hmac).
>
> Note that as a side-effect of this patch algorithms which are not
> FIPS-allowed will now return ENOENT instead of ELIBBAD.  Hopefully
> this is not an issue as some people were relying on this already.
>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
>
> diff --git a/crypto/algapi.c b/crypto/algapi.c
> index a366cb3e8aa1..09fb75806e87 100644
> --- a/crypto/algapi.c
> +++ b/crypto/algapi.c
> @@ -322,8 +322,16 @@ void crypto_alg_tested(const char *name, int err)
>  found:
>  	q->cra_flags |= CRYPTO_ALG_DEAD;
>  	alg = test->adult;
> -	if (err || list_empty(&alg->cra_list))
> +
> +	if (list_empty(&alg->cra_list))
> +		goto complete;
> +
> +	if (err == -ECANCELED)
> +		alg->cra_flags |= CRYPTO_ALG_FIPS_INTERNAL;
> +	else if (err)
>  		goto complete;
> +	else
> +		alg->cra_flags &= ~CRYPTO_ALG_FIPS_INTERNAL;
>  
>  	alg->cra_flags |= CRYPTO_ALG_TESTED;
>  
> diff --git a/crypto/api.c b/crypto/api.c
> index cf0869dd130b..549f9aced1da 100644
> --- a/crypto/api.c
> +++ b/crypto/api.c
> @@ -223,6 +223,8 @@ static struct crypto_alg *crypto_larval_wait(struct crypto_alg *alg)
>  	else if (crypto_is_test_larval(larval) &&
>  		 !(alg->cra_flags & CRYPTO_ALG_TESTED))
>  		alg = ERR_PTR(-EAGAIN);
> +	else if (alg->cra_flags & CRYPTO_ALG_FIPS_INTERNAL)
> +		alg = ERR_PTR(-EAGAIN);

I might be mistaken, but I think this would cause hmac(sha1)
instantiation to fail if sha1 is not already there. I.e. if hmac(sha1)
instantiation would load sha1, then it would invoke crypto_larval_wait()
on the sha1 larval, see the FIPS_INTERNAL and fail?

However, wouldn't it be possible to simply implement FIPS_INTERNAL
lookups in analogy to the INTERNAL ones instead? That is, would adding

	if (!((type | mask) & CRYPTO_ALG_FIPS_INTERNAL))
		mask |= CRYPTO_ALG_FIPS_INTERNAL;

to the preamble of crypto_alg_mod_lookup() work instead?

AFAICS, ...


>  	else if (!crypto_mod_get(alg))
>  		alg = ERR_PTR(-EAGAIN);
>  	crypto_mod_put(&larval->alg);
> @@ -233,6 +235,7 @@ static struct crypto_alg *crypto_larval_wait(struct crypto_alg *alg)
>  static struct crypto_alg *crypto_alg_lookup(const char *name, u32 type,
>  					    u32 mask)
>  {
> +	const u32 fips = CRYPTO_ALG_FIPS_INTERNAL;
>  	struct crypto_alg *alg;
>  	u32 test = 0;
>  
> @@ -240,8 +243,20 @@ static struct crypto_alg *crypto_alg_lookup(const char *name, u32 type,
>  		test |= CRYPTO_ALG_TESTED;
>  
>  	down_read(&crypto_alg_sem);
> -	alg = __crypto_alg_lookup(name, type | test, mask | test);
> -	if (!alg && test) {
> +	alg = __crypto_alg_lookup(name, (type | test) & ~fips,
> +				  (mask | test) & ~fips);
> +	if (alg) {
> +		if (((type | mask) ^ fips) & fips)
> +			mask |= fips;
> +		mask &= fips;
> +
> +		if (!crypto_is_larval(alg) &&
> +		    ((type ^ alg->cra_flags) & mask)) {
> +			/* Algorithm is disallowed in FIPS mode. */
> +			crypto_mod_put(alg);
> +			alg = ERR_PTR(-ENOENT);
> +		}
> +	} else if (test) {

... this check here would not be needed anymore then? But I might be
missing something.


>  		alg = __crypto_alg_lookup(name, type, mask);
>  		if (alg && !crypto_is_larval(alg)) {
>  			/* Test failed */
> diff --git a/crypto/hmac.c b/crypto/hmac.c
> index 25856aa7ccbf..af82e3eeb7d0 100644
> --- a/crypto/hmac.c
> +++ b/crypto/hmac.c
> @@ -169,6 +169,7 @@ static int hmac_create(struct crypto_template *tmpl, struct rtattr **tb)
>  	struct crypto_alg *alg;
>  	struct shash_alg *salg;
>  	u32 mask;
> +	u32 type;
>  	int err;
>  	int ds;
>  	int ss;
> @@ -182,8 +183,9 @@ static int hmac_create(struct crypto_template *tmpl, struct rtattr **tb)
>  		return -ENOMEM;
>  	spawn = shash_instance_ctx(inst);
>  
> +	type = CRYPTO_ALG_FIPS_INTERNAL;
>  	err = crypto_grab_shash(spawn, shash_crypto_instance(inst),
> -				crypto_attr_alg_name(tb[1]), 0, mask);
> +				crypto_attr_alg_name(tb[1]), type, mask);
>  	if (err)
>  		goto err_free_inst;
>  	salg = crypto_spawn_shash_alg(spawn);
> @@ -204,6 +206,7 @@ static int hmac_create(struct crypto_template *tmpl, struct rtattr **tb)
>  	if (err)
>  		goto err_free_inst;
>  
> +	inst->alg.base.cra_flags = alg->cra_flags & CRYPTO_ALG_FIPS_INTERNAL;
>  	inst->alg.base.cra_priority = alg->cra_priority;
>  	inst->alg.base.cra_blocksize = alg->cra_blocksize;
>  	inst->alg.base.cra_alignmask = alg->cra_alignmask;
> diff --git a/crypto/testmgr.c b/crypto/testmgr.c
> index 5831d4bbc64f..995d44db6154 100644
> --- a/crypto/testmgr.c
> +++ b/crypto/testmgr.c
> @@ -1664,7 +1664,8 @@ static int test_hash_vs_generic_impl(const char *generic_driver,
>  	if (strcmp(generic_driver, driver) == 0) /* Already the generic impl? */
>  		return 0;
>  
> -	generic_tfm = crypto_alloc_shash(generic_driver, 0, 0);
> +	generic_tfm = crypto_alloc_shash(generic_driver,
> +					 CRYPTO_ALG_FIPS_INTERNAL, 0);
>  	if (IS_ERR(generic_tfm)) {
>  		err = PTR_ERR(generic_tfm);
>  		if (err == -ENOENT) {
> @@ -2387,7 +2388,8 @@ static int test_aead_vs_generic_impl(struct aead_extra_tests_ctx *ctx)
>  	if (strcmp(generic_driver, driver) == 0) /* Already the generic impl? */
>  		return 0;
>  
> -	generic_tfm = crypto_alloc_aead(generic_driver, 0, 0);
> +	generic_tfm = crypto_alloc_aead(generic_driver,
> +					CRYPTO_ALG_FIPS_INTERNAL, 0);
>  	if (IS_ERR(generic_tfm)) {
>  		err = PTR_ERR(generic_tfm);
>  		if (err == -ENOENT) {
> @@ -2986,7 +2988,8 @@ static int test_skcipher_vs_generic_impl(const char *generic_driver,
>  	if (strcmp(generic_driver, driver) == 0) /* Already the generic impl? */
>  		return 0;
>  
> -	generic_tfm = crypto_alloc_skcipher(generic_driver, 0, 0);
> +	generic_tfm = crypto_alloc_skcipher(generic_driver,
> +					    CRYPTO_ALG_FIPS_INTERNAL, 0);
>  	if (IS_ERR(generic_tfm)) {
>  		err = PTR_ERR(generic_tfm);
>  		if (err == -ENOENT) {
> @@ -5328,7 +5331,6 @@ static const struct alg_test_desc alg_test_descs[] = {
>  	}, {
>  		.alg = "sha1",
>  		.test = alg_test_hash,
> -		.fips_allowed = 1,
>  		.suite = {
>  			.hash = __VECS(sha1_tv_template)
>  		}
> @@ -5613,6 +5615,13 @@ static int alg_find_test(const char *alg)
>  	return -1;
>  }
>  
> +static int alg_fips_disabled(const char *driver, const char *alg)
> +{
> +	pr_info("alg: %s (%s) is disabled due to FIPS\n", alg, driver);
> +
> +	return -ECANCELED;
> +}
> +
>  int alg_test(const char *driver, const char *alg, u32 type, u32 mask)
>  {
>  	int i;
> @@ -5637,9 +5646,6 @@ int alg_test(const char *driver, const char *alg, u32 type, u32 mask)
>  		if (i < 0)
>  			goto notest;
>  
> -		if (fips_enabled && !alg_test_descs[i].fips_allowed)
> -			goto non_fips_alg;
> -
>  		rc = alg_test_cipher(alg_test_descs + i, driver, type, mask);
>  		goto test_done;
>  	}
> @@ -5649,8 +5655,7 @@ int alg_test(const char *driver, const char *alg, u32 type, u32 mask)
>  	if (i < 0 && j < 0)
>  		goto notest;
>  
> -	if (fips_enabled && ((i >= 0 && !alg_test_descs[i].fips_allowed) ||
> -			     (j >= 0 && !alg_test_descs[j].fips_allowed)))
> +	if (fips_enabled && (j >= 0 && !alg_test_descs[j].fips_allowed))
>  		goto non_fips_alg;
>  
>  	rc = 0;
> @@ -5671,16 +5676,22 @@ int alg_test(const char *driver, const char *alg, u32 type, u32 mask)
>  		}
>  		WARN(1, "alg: self-tests for %s (%s) failed (rc=%d)",
>  		     driver, alg, rc);
> -	} else {
> -		if (fips_enabled)
> -			pr_info("alg: self-tests for %s (%s) passed\n",
> -				driver, alg);
> +	} else if (fips_enabled) {
> +		pr_info("alg: self-tests for %s (%s) passed\n",
> +			driver, alg);
> +
> +		if (i >= 0 && !alg_test_descs[i].fips_allowed)
> +			rc = alg_fips_disabled(driver, alg);
>  	}
>  
>  	return rc;
>  
>  notest:
>  	printk(KERN_INFO "alg: No test for %s (%s)\n", alg, driver);
> +
> +	if (type & CRYPTO_ALG_FIPS_INTERNAL)
> +		return alg_fips_disabled(driver, alg);
> +
>  	return 0;
>  non_fips_alg:
>  	return -EINVAL;

This looks all good to me, but as !->fips_allowed tests aren't skipped
over anymore now, it would perhaps make sense to make their failure
non-fatal in FIPS mode. Because in FIPS mode a failure could mean a
panic and some of the existing TVs might not pass because of e.g. some
key length checks or so active only for fips_enabled...

Many thanks again!

Nicolai



> diff --git a/include/linux/crypto.h b/include/linux/crypto.h
> index 855869e1fd32..df3f68dfe8c7 100644
> --- a/include/linux/crypto.h
> +++ b/include/linux/crypto.h
> @@ -132,6 +132,15 @@
>   */
>  #define CRYPTO_ALG_ALLOCATES_MEMORY	0x00010000
>  
> +/*
> + * Mark an algorithm as a service implementation only usable by a
> + * template and never by a normal user of the kernel crypto API.
> + * This is intended to be used by algorithms that are themselves
> + * not FIPS-approved but may instead be used to implement parts of
> + * a FIPS-approved algorithm (e.g., sha1 vs. hmac(sha1)).
> + */
> +#define CRYPTO_ALG_FIPS_INTERNAL	0x00020000
> +
>  /*
>   * Transform masks and values (for crt_flags).
>   */

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