[v2 PATCH] crypto: api - fix unexpectedly getting generic implementation

Herbert Xu
2019-12-04T09:19:15Z

Eric Biggers <ebiggers@kernel.org> wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> When CONFIG_CRYPTO_MANAGER_EXTRA_TESTS=y, the first lookup of an
> algorithm that needs to be instantiated using a template will always get
> the generic implementation, even when an accelerated one is available.
>
> This happens because the extra self-tests for the accelerated
> implementation allocate the generic implementation for comparison
> purposes, and then crypto_alg_tested() for the generic implementation
> "fulfills" the original request (i.e. sets crypto_larval::adult).
>
> Fix this by making crypto_alg_tested() replace an already-set
> crypto_larval::adult when it has lower priority and the larval hasn't
> already been complete()d (by cryptomgr_probe()).
>
> This also required adding crypto_alg_sem protection to completing the
> larval in cryptomgr_probe().
>
> Also add some comments to crypto_alg_tested() to make it easier to
> understand what's going on.
>
> Fixes: 9a8a6b3f0950 ("crypto: testmgr - fuzz hashes against their generic implementation")
> Fixes: d435e10e67be ("crypto: testmgr - fuzz skciphers against their generic implementation")
> Fixes: 40153b10d91c ("crypto: testmgr - fuzz AEADs against their generic implementation")
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
> crypto/algapi.c | 46 +++++++++++++++++++++++++++++++++++++++++-----
> crypto/algboss.c | 4 ++++
> crypto/api.c | 5 -----
> crypto/internal.h | 5 +++++
> 4 files changed, 50 insertions(+), 10 deletions(-)

Thanks for the patch! I had forgotten about this problem :)

> @@ -290,26 +302,50 @@ void crypto_alg_tested(const char *name, int err)
> if (crypto_is_larval(q)) {
> struct crypto_larval *larval = (void *)q;
>
> + if (crypto_is_test_larval(larval))
> + continue;
> +
> /*
> - * Check to see if either our generic name or
> - * specific name can satisfy the name requested
> - * by the larval entry q.
> + * Fulfill the request larval 'q' (set larval->adult) if
> + * the tested algorithm is compatible with it, i.e. if
> + * the request is for the same generic or driver name
> + * and for compatible flags.
> + *
> + * If larval->adult is already set, replace it if the
> + * tested algorithm is higher priority and the larval
> + * hasn't been completed()d yet. This is needed to
> + * avoid users always getting the generic implementation
> + * on first use when the extra self-tests are enabled.
> */
> +
> if (strcmp(alg->cra_name, q->cra_name) &&
> strcmp(alg->cra_driver_name, q->cra_name))
> continue;
>
> - if (larval->adult)
> - continue;
> if ((q->cra_flags ^ alg->cra_flags) & larval->mask)
> continue;
> +
> + if (larval->adult &&
> + larval->adult->cra_priority >= alg->cra_priority)
> + continue;
> +
> + if (completion_done(&larval->completion))
> + continue;
> +
> if (!crypto_mod_get(alg))
> continue;
>
> + if (larval->adult)
> + crypto_mod_put(larval->adult);
> larval->adult = alg;
> continue;
> }

I think this is a tad over-complicated. All we really need to do
is avoid changing larval->adult if we are not the best larval.
Something like this (totally untested!):

---8<---
When CONFIG_CRYPTO_MANAGER_EXTRA_TESTS=y, the first lookup of an
algorithm that needs to be instantiated using a template will always get
the generic implementation, even when an accelerated one is available.

This happens because the extra self-tests for the accelerated
implementation allocate the generic implementation for comparison
purposes, and then crypto_alg_tested() for the generic implementation
"fulfills" the original request (i.e. sets crypto_larval::adult).

This patch fixes this by only fulfilling the original request if
we are currently the best outstanding larval as judged by the
priority.

Fixes: 9a8a6b3f0950 ("crypto: testmgr - fuzz hashes against their generic implementation")
Fixes: d435e10e67be ("crypto: testmgr - fuzz skciphers against their generic implementation")
Fixes: 40153b10d91c ("crypto: testmgr - fuzz AEADs against their generic implementation")
Reported-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/algapi.c b/crypto/algapi.c
index b052f38edba6..3e65653735f4 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -280,6 +280,18 @@ void crypto_alg_tested(const char *name, int err)

alg->cra_flags |= CRYPTO_ALG_TESTED;

+ /* Only satisfy larval waiters if we are the best. */
+ list_for_each_entry(q, &crypto_alg_list, cra_list) {
+ if (!crypto_is_larval(q))
+ continue;
+
+ if (strcmp(alg->cra_name, q->cra_name))
+ continue;
+
+ if (q->cra_priority > alg->cra_priority)
+ goto complete;
+ }
+
list_for_each_entry(q, &crypto_alg_list, cra_list) {
if (q == alg)
continue;
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt