From: Eric Biggers ebiggers@google.com

GCM instances can be created by either the "gcm" template, which only allows choosing the block cipher, e.g. "gcm(aes)"; or by "gcm_base", which allows choosing the ctr and ghash implementations, e.g. "gcm_base(ctr(aes-generic),ghash-generic)".

However, a "gcm_base" instance prevents a "gcm" instance from being registered using the same implementations. Nor will the instance be found by lookups of "gcm". This can be used as a denial of service. Moreover, "gcm_base" instances are never tested by the crypto self-tests, even if there are compatible "gcm" tests.

The root cause of these problems is that instances of the two templates use different cra_names. Therefore, fix these problems by making "gcm_base" instances set the same cra_name as "gcm" instances, e.g. "gcm(aes)" instead of "gcm_base(ctr(aes-generic),ghash-generic)".

This requires extracting the block cipher name from the name of the ctr algorithm. It also requires starting to verify that the algorithms are really ctr and ghash, not something else entirely. But it would be bizarre if anyone were actually using non-gcm-compatible algorithms with gcm_base, so this shouldn't break anyone in practice.

Fixes: d00aa19b507b ("[CRYPTO] gcm: Allow block cipher parameter") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@google.com --- crypto/gcm.c | 32 +++++++++----------------------- 1 file changed, 9 insertions(+), 23 deletions(-)

diff --git a/crypto/gcm.c b/crypto/gcm.c index e1a11f529d257..c7354ed1fa4d4 100644 --- a/crypto/gcm.c +++ b/crypto/gcm.c @@ -597,7 +597,6 @@ static void crypto_gcm_free(struct aead_instance *inst)

static int crypto_gcm_create_common(struct crypto_template *tmpl, struct rtattr **tb, - const char *full_name, const char *ctr_name, const char *ghash_name) { @@ -638,7 +637,7 @@ static int crypto_gcm_create_common(struct crypto_template *tmpl, goto err_free_inst;

err = -EINVAL; - if (ghash->digestsize != 16) + if (strcmp(ghash->base.cra_name, "ghash") != 0) goto err_drop_ghash;

crypto_set_skcipher_spawn(&ctx->ctr, aead_crypto_instance(inst)); @@ -650,24 +649,23 @@ static int crypto_gcm_create_common(struct crypto_template *tmpl,

ctr = crypto_spawn_skcipher_alg(&ctx->ctr);

- /* We only support 16-byte blocks. */ + /* The skcipher algorithm must be CTR mode, using 16-byte blocks. */ err = -EINVAL; - if (crypto_skcipher_alg_ivsize(ctr) != 16) + if (strncmp(ctr->base.cra_name, "ctr(", 4) != 0 || + crypto_skcipher_alg_ivsize(ctr) != 16) goto out_put_ctr;

- /* Not a stream cipher? */ - if (ctr->base.cra_blocksize != 1) + err = -ENAMETOOLONG; + if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME, + "gcm(%s", ctr->base.cra_name + 4) >= CRYPTO_MAX_ALG_NAME) goto out_put_ctr;

- err = -ENAMETOOLONG; if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME, "gcm_base(%s,%s)", ctr->base.cra_driver_name, ghash_alg->cra_driver_name) >= CRYPTO_MAX_ALG_NAME) goto out_put_ctr;

- memcpy(inst->alg.base.cra_name, full_name, CRYPTO_MAX_ALG_NAME); - inst->alg.base.cra_flags = (ghash->base.cra_flags | ctr->base.cra_flags) & CRYPTO_ALG_ASYNC; inst->alg.base.cra_priority = (ghash->base.cra_priority + @@ -709,7 +707,6 @@ static int crypto_gcm_create(struct crypto_template *tmpl, struct rtattr **tb) { const char *cipher_name; char ctr_name[CRYPTO_MAX_ALG_NAME]; - char full_name[CRYPTO_MAX_ALG_NAME];

cipher_name = crypto_attr_alg_name(tb[1]); if (IS_ERR(cipher_name)) @@ -719,12 +716,7 @@ static int crypto_gcm_create(struct crypto_template *tmpl, struct rtattr **tb) CRYPTO_MAX_ALG_NAME) return -ENAMETOOLONG;

- if (snprintf(full_name, CRYPTO_MAX_ALG_NAME, "gcm(%s)", cipher_name) >= - CRYPTO_MAX_ALG_NAME) - return -ENAMETOOLONG; - - return crypto_gcm_create_common(tmpl, tb, full_name, - ctr_name, "ghash"); + return crypto_gcm_create_common(tmpl, tb, ctr_name, "ghash"); }

static int crypto_gcm_base_create(struct crypto_template *tmpl, @@ -732,7 +724,6 @@ static int crypto_gcm_base_create(struct crypto_template *tmpl, { const char *ctr_name; const char *ghash_name; - char full_name[CRYPTO_MAX_ALG_NAME];

ctr_name = crypto_attr_alg_name(tb[1]); if (IS_ERR(ctr_name)) @@ -742,12 +733,7 @@ static int crypto_gcm_base_create(struct crypto_template *tmpl, if (IS_ERR(ghash_name)) return PTR_ERR(ghash_name);

- if (snprintf(full_name, CRYPTO_MAX_ALG_NAME, "gcm_base(%s,%s)", - ctr_name, ghash_name) >= CRYPTO_MAX_ALG_NAME) - return -ENAMETOOLONG; - - return crypto_gcm_create_common(tmpl, tb, full_name, - ctr_name, ghash_name); + return crypto_gcm_create_common(tmpl, tb, ctr_name, ghash_name); }

static int crypto_rfc4106_setkey(struct crypto_aead *parent, const u8 *key,