[fixed mhalcrow's email address] Hi Dan - thanks for the alert. I think the code is fine in this situation.
On 2016-01-25 17:23:11, Dan Carpenter wrote:
> Hello Michael Halcrow,
>
> The patch e5d9cbde6ce0: "[PATCH] eCryptfs: Clean up crypto
> initialization" from Oct 30, 2006, leads to the following static
> checker warning:
>
> fs/ecryptfs/crypto.c:1625 ecryptfs_process_key_cipher()
> error: get_random_bytes() 'dummy_key' too small (64 vs 4294967295)
>
> fs/ecryptfs/crypto.c
> 1593 static int
> 1594 ecryptfs_process_key_cipher(struct crypto_blkcipher **key_tfm,
> 1595 char *cipher_name, size_t *key_size)
> 1596 {
> 1597 char dummy_key[ECRYPTFS_MAX_KEY_BYTES];
> 1598 char *full_alg_name = NULL;
> 1599 int rc;
> 1600
> 1601 *key_tfm = NULL;
> 1602 if (*key_size > ECRYPTFS_MAX_KEY_BYTES) {
> 1603 rc = -EINVAL;
> 1604 printk(KERN_ERR "Requested key size is [%zd] bytes;
> maximum "
> 1605 "allowable is [%d]\n", *key_size,
> ECRYPTFS_MAX_KEY_BYTES);
> 1606 goto out;
> 1607 }
> 1608 rc = ecryptfs_crypto_api_algify_cipher_name(&full_alg_name,
> cipher_name,
> 1609 "ecb");
> 1610 if (rc)
> 1611 goto out;
> 1612 *key_tfm = crypto_alloc_blkcipher(full_alg_name, 0,
> CRYPTO_ALG_ASYNC);
> 1613 if (IS_ERR(*key_tfm)) {
> 1614 rc = PTR_ERR(*key_tfm);
> 1615 printk(KERN_ERR "Unable to allocate crypto cipher
> with name "
> 1616 "[%s]; rc = [%d]\n", full_alg_name, rc);
> 1617 goto out;
> 1618 }
> 1619 crypto_blkcipher_set_flags(*key_tfm, CRYPTO_TFM_REQ_WEAK_KEY);
> 1620 if (*key_size == 0) {
> 1621 struct blkcipher_alg *alg =
> crypto_blkcipher_alg(*key_tfm);
> 1622
> 1623 *key_size = alg->max_keysize;
>
> My concern here is that arc4 has a max_keysize of ARC4_MAX_KEY_SIZE (256).
>
> 1624 }
> 1625 get_random_bytes(dummy_key, *key_size);
>
> Potentially leading to memory corruption here. This is static analysis
> work so I may be wrong.
There are two things stopping this from being an issue. The first is the
check on key_size at line 1602. The second is that eCryptfs only
supports a small set of ciphers that have max key sizes well within
ECRYPTFS_MAX_KEY_BYTES:
fs/ecryptfs/crypto.c
962 /* Add support for additional ciphers by adding elements here. The
963 * cipher_code is whatever OpenPGP applicatoins use to identify the
964 * ciphers. List in order of probability. */
965 static struct ecryptfs_cipher_code_str_map_elem
966 ecryptfs_cipher_code_str_map[] = {
967 {"aes",RFC2440_CIPHER_AES_128 },
968 {"blowfish", RFC2440_CIPHER_BLOWFISH},
969 {"des3_ede", RFC2440_CIPHER_DES3_EDE},
970 {"cast5", RFC2440_CIPHER_CAST_5},
971 {"twofish", RFC2440_CIPHER_TWOFISH},
972 {"cast6", RFC2440_CIPHER_CAST_6},
973 {"aes", RFC2440_CIPHER_AES_192},
974 {"aes", RFC2440_CIPHER_AES_256}
975 };
Tyler
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