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crypto: hash - set CRYPTO_TFM_NEED_KEY if ->setkey() fails

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Some algorithms have a ->setkey() method that is not atomic, in the
sense that setting a key can fail after changes were already made to the
tfm context.  In this case, if a key was already set the tfm can end up
in a state that corresponds to neither the old key nor the new key.

It's not feasible to make all ->setkey() methods atomic, especially ones
that have to key multiple sub-tfms.  Therefore, make the crypto API set
CRYPTO_TFM_NEED_KEY if ->setkey() fails and the algorithm requires a
key, to prevent the tfm from being used until a new key is set.

Note: we can't set CRYPTO_TFM_NEED_KEY for OPTIONAL_KEY algorithms, so
->setkey() for those must nevertheless be atomic.  That's fine for now
since only the crc32 and crc32c algorithms set OPTIONAL_KEY, and it's
not intended that OPTIONAL_KEY be used much.

[Cc stable mainly because when introducing the NEED_KEY flag I changed
 AF_ALG to rely on it; and unlike in-kernel crypto API users, AF_ALG
 previously didn't have this problem.  So these "incompletely keyed"
 states became theoretically accessible via AF_ALG -- though, the
 opportunities for causing real mischief seem pretty limited.]

Fixes: 9fa68f6200 ("crypto: hash - prevent using keyed hashes without setting key")
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>
This commit is contained in:
Eric Biggers 2019-01-06 18:47:42 -08:00 • committed by Herbert Xu
commit ba7d7433a0
2 changed files with 32 additions and 14 deletions
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28
crypto/ahash.c
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@ -190,6 +190,21 @@ static int ahash_setkey_unaligned(struct crypto_ahash *tfm, const u8 *key,
return ret;
}
static int ahash_nosetkey(struct crypto_ahash *tfm, const u8 *key,
unsigned int keylen)
{
return -ENOSYS;
}
static void ahash_set_needkey(struct crypto_ahash *tfm)
{
const struct hash_alg_common *alg = crypto_hash_alg_common(tfm);
if (tfm->setkey != ahash_nosetkey &&
!(alg->base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY))
crypto_ahash_set_flags(tfm, CRYPTO_TFM_NEED_KEY);
}
int crypto_ahash_setkey(struct crypto_ahash *tfm, const u8 *key,
unsigned int keylen)
{
@ -201,20 +216,16 @@ int crypto_ahash_setkey(struct crypto_ahash *tfm, const u8 *key,
else
err = tfm->setkey(tfm, key, keylen);
if (err)
if (unlikely(err)) {
ahash_set_needkey(tfm);
return err;
}
crypto_ahash_clear_flags(tfm, CRYPTO_TFM_NEED_KEY);
return 0;
}
EXPORT_SYMBOL_GPL(crypto_ahash_setkey);
static int ahash_nosetkey(struct crypto_ahash *tfm, const u8 *key,
unsigned int keylen)
{
return -ENOSYS;
}
static inline unsigned int ahash_align_buffer_size(unsigned len,
unsigned long mask)
{
@ -489,8 +500,7 @@ static int crypto_ahash_init_tfm(struct crypto_tfm *tfm)
if (alg->setkey) {
hash->setkey = alg->setkey;
if (!(alg->halg.base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY))
crypto_ahash_set_flags(hash, CRYPTO_TFM_NEED_KEY);
ahash_set_needkey(hash);
}
return 0;