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KEYS: encrypted: fix race causing incorrect HMAC calculations

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The encrypted-keys module was using a single global HMAC transform,
which could be rekeyed by multiple threads concurrently operating on
different keys, causing incorrect HMAC values to be calculated.  Fix
this by allocating a new HMAC transform whenever we need to calculate a
HMAC.  Also simplify things a bit by allocating the shash_desc's using
SHASH_DESC_ON_STACK() for both the HMAC and unkeyed hashes.

The following script reproduces the bug:

    keyctl new_session
    keyctl add user master "abcdefghijklmnop" @s
    for i in $(seq 2); do
        (
            set -e
            for j in $(seq 1000); do
                keyid=$(keyctl add encrypted desc$i "new user:master 25" @s)
                datablob="$(keyctl pipe $keyid)"
                keyctl unlink $keyid > /dev/null
                keyid=$(keyctl add encrypted desc$i "load $datablob" @s)
                keyctl unlink $keyid > /dev/null
            done
        ) &
    done

Output with bug:

    [  439.691094] encrypted_key: bad hmac (-22)
    add_key: Invalid argument
    add_key: Invalid argument

Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
This commit is contained in:
Eric Biggers 2017-06-08 14:48:25 +01:00 committed by James Morris
parent 794b4bc292
commit 64d107d3ac
1 changed files with 33 additions and 84 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

117
security/keys/encrypted-keys/encrypted.c
View File

@ -54,13 +54,7 @@ static int blksize;
#define MAX_DATA_SIZE 4096
#define MIN_DATA_SIZE 20
struct sdesc {
struct shash_desc shash;
char ctx[];
};
static struct crypto_shash *hashalg;
static struct crypto_shash *hmacalg;
static struct crypto_shash *hash_tfm;
enum {
Opt_err = -1, Opt_new, Opt_load, Opt_update
@ -320,53 +314,38 @@ error:
return ukey;
}
static struct sdesc *alloc_sdesc(struct crypto_shash *alg)
static int calc_hash(struct crypto_shash *tfm, u8 *digest,
const u8 *buf, unsigned int buflen)
{
struct sdesc *sdesc;
int size;
SHASH_DESC_ON_STACK(desc, tfm);
int err;
size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
sdesc = kmalloc(size, GFP_KERNEL);
if (!sdesc)
return ERR_PTR(-ENOMEM);
sdesc->shash.tfm = alg;
sdesc->shash.flags = 0x0;
return sdesc;
desc->tfm = tfm;
desc->flags = 0;
err = crypto_shash_digest(desc, buf, buflen, digest);
shash_desc_zero(desc);
return err;
}
static int calc_hmac(u8 *digest, const u8 *key, unsigned int keylen,
const u8 *buf, unsigned int buflen)
{
struct sdesc *sdesc;
int ret;
struct crypto_shash *tfm;
int err;
sdesc = alloc_sdesc(hmacalg);
if (IS_ERR(sdesc)) {
pr_info("encrypted_key: can't alloc %s\n", hmac_alg);
return PTR_ERR(sdesc);
tfm = crypto_alloc_shash(hmac_alg, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(tfm)) {
pr_err("encrypted_key: can't alloc %s transform: %ld\n",
hmac_alg, PTR_ERR(tfm));
return PTR_ERR(tfm);
}
ret = crypto_shash_setkey(hmacalg, key, keylen);
if (!ret)
ret = crypto_shash_digest(&sdesc->shash, buf, buflen, digest);
kfree(sdesc);
return ret;
}
static int calc_hash(u8 *digest, const u8 *buf, unsigned int buflen)
{
struct sdesc *sdesc;
int ret;
sdesc = alloc_sdesc(hashalg);
if (IS_ERR(sdesc)) {
pr_info("encrypted_key: can't alloc %s\n", hash_alg);
return PTR_ERR(sdesc);
}
ret = crypto_shash_digest(&sdesc->shash, buf, buflen, digest);
kfree(sdesc);
return ret;
err = crypto_shash_setkey(tfm, key, keylen);
if (!err)
err = calc_hash(tfm, digest, buf, buflen);
crypto_free_shash(tfm);
return err;
}
enum derived_key_type { ENC_KEY, AUTH_KEY };
@ -394,7 +373,7 @@ static int get_derived_key(u8 *derived_key, enum derived_key_type key_type,
memcpy(derived_buf + strlen(derived_buf) + 1, master_key,
master_keylen);
ret = calc_hash(derived_key, derived_buf, derived_buf_len);
ret = calc_hash(hash_tfm, derived_key, derived_buf, derived_buf_len);
kfree(derived_buf);
return ret;
}
@ -998,47 +977,17 @@ struct key_type key_type_encrypted = {
};
EXPORT_SYMBOL_GPL(key_type_encrypted);
static void encrypted_shash_release(void)
{
if (hashalg)
crypto_free_shash(hashalg);
if (hmacalg)
crypto_free_shash(hmacalg);
}
static int __init encrypted_shash_alloc(void)
{
int ret;
hmacalg = crypto_alloc_shash(hmac_alg, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(hmacalg)) {
pr_info("encrypted_key: could not allocate crypto %s\n",
hmac_alg);
return PTR_ERR(hmacalg);
}
hashalg = crypto_alloc_shash(hash_alg, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(hashalg)) {
pr_info("encrypted_key: could not allocate crypto %s\n",
hash_alg);
ret = PTR_ERR(hashalg);
goto hashalg_fail;
}
return 0;
hashalg_fail:
crypto_free_shash(hmacalg);
return ret;
}
static int __init init_encrypted(void)
{
int ret;
ret = encrypted_shash_alloc();
if (ret < 0)
return ret;
hash_tfm = crypto_alloc_shash(hash_alg, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(hash_tfm)) {
pr_err("encrypted_key: can't allocate %s transform: %ld\n",
hash_alg, PTR_ERR(hash_tfm));
return PTR_ERR(hash_tfm);
}
ret = aes_get_sizes();
if (ret < 0)
goto out;
@ -1047,14 +996,14 @@ static int __init init_encrypted(void)
goto out;
return 0;
out:
encrypted_shash_release();
crypto_free_shash(hash_tfm);
return ret;
}
static void __exit cleanup_encrypted(void)
{
encrypted_shash_release();
crypto_free_shash(hash_tfm);
unregister_key_type(&key_type_encrypted);
}