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Date: Wed, 13 Nov 2013 13:45:49 -0500
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: David Howells <dhowells@...hat.com>
Cc: d.kasatkin@...sung.com, zohar@...ibm.com, keyrings@...ux-nfs.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] KEYS: Fix encrypted key type update method
On Mon, 2013-11-04 at 16:23 +0000, David Howells wrote:
> The encrypted key type was using the update method to change the master key
> used to encrypt a key without passing in all the requisite parameters to
> completely replace the key contents (it was taking some parameters from the
> old key contents). Unfortunately, this has a number of problems:
>
> (1) Update is conceptually meant to be the same as add_key() except that it
> replaces the contents of the nominated key completely rather than creating
> a new key.
>
> (2) add_key() can call ->update() if it detects that the key exists. This can
> cause the operation to fail if the caller embedded the wrong command in
> the payload when they called it. The caller cannot know what the right
> command is without someway to lock the keyring.
>
> (3) keyctl_update() and add_key() can thus race with adding, linking,
> requesting and unlinking a key.
>
> The best way to fix this is to offload this operation to keyctl_control() and
> make encrypted_update() just replace the contents of a key entirely (or maybe
> just not permit updates if this would be a problem).
>
> Signed-off-by: David Howells <dhowells@...hat.com>
The code looks good, other than breaking the existing userspace/kernel
API, but I haven't tested it yet. Is there a keyutils git repo with a
version of keyctl that supports the control option?
A couple of minor comments:
- type size_t is unsigned, no need to verify that it is negative.
- missing Documentation/security/keys-trusted-encrypted.txt updates
- the encrypted_preparse() comment still says 'encrypted_instantiate'
thanks,
Mimi
> ---
>
> security/keys/encrypted-keys/encrypted.c | 101 ++++++++++++++----------------
> 1 file changed, 47 insertions(+), 54 deletions(-)
>
> diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
> index f9e7b808fa47..c9e4fa5b1e2c 100644
> --- a/security/keys/encrypted-keys/encrypted.c
> +++ b/security/keys/encrypted-keys/encrypted.c
> @@ -595,7 +595,7 @@ out:
> }
>
> /* Allocate memory for decrypted key and datablob. */
> -static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
> +static struct encrypted_key_payload *encrypted_key_alloc(size_t *_quotalen,
> const char *format,
> const char *master_desc,
> const char *datalen)
> @@ -632,10 +632,7 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
> datablob_len = format_len + 1 + strlen(master_desc) + 1
> + strlen(datalen) + 1 + ivsize + 1 + encrypted_datalen;
>
> - ret = key_payload_reserve(key, payload_datalen + datablob_len
> - + HASH_SIZE + 1);
> - if (ret < 0)
> - return ERR_PTR(ret);
> + *_quotalen = payload_datalen + datablob_len + HASH_SIZE + 1;
>
> epayload = kzalloc(sizeof(*epayload) + payload_datalen +
> datablob_len + HASH_SIZE + 1, GFP_KERNEL);
> @@ -773,8 +770,7 @@ static int encrypted_init(struct encrypted_key_payload *epayload,
> *
> * On success, return 0. Otherwise return errno.
> */
> -static int encrypted_instantiate(struct key *key,
> - struct key_preparsed_payload *prep)
> +static int encrypted_preparse(struct key_preparsed_payload *prep)
> {
> struct encrypted_key_payload *epayload = NULL;
> char *datablob = NULL;
> @@ -798,25 +794,55 @@ static int encrypted_instantiate(struct key *key,
> if (ret < 0)
> goto out;
>
> - epayload = encrypted_key_alloc(key, format, master_desc,
> + epayload = encrypted_key_alloc(&prep->quotalen, format, master_desc,
> decrypted_datalen);
> if (IS_ERR(epayload)) {
> ret = PTR_ERR(epayload);
> goto out;
> }
> - ret = encrypted_init(epayload, key->description, format, master_desc,
> + ret = encrypted_init(epayload, prep->description, format, master_desc,
> decrypted_datalen, hex_encoded_iv);
> if (ret < 0) {
> kfree(epayload);
> goto out;
> }
>
> - rcu_assign_keypointer(key, epayload);
> + prep->payload[0] = epayload;
> +
> out:
> kfree(datablob);
> return ret;
> }
>
> +/*
> + * encrypted_free_preparse - Clean up preparse data for an encrypted key
> + */
> +static void encrypted_free_preparse(struct key_preparsed_payload *prep)
> +{
> + struct encrypted_key_payload *epayload = prep->payload[0];
> +
> + if (epayload) {
> + memset(epayload->decrypted_data, 0,
> + epayload->decrypted_datalen);
> + kfree(epayload);
> + }
> +}
> +
> +static int encrypted_instantiate(struct key *key,
> + struct key_preparsed_payload *prep)
> +{
> + struct encrypted_key_payload *epayload = prep->payload[0];
> + int ret;
> +
> + ret = key_payload_reserve(key, prep->quotalen);
> + if (ret < 0)
> + return ret;
> +
> + rcu_assign_keypointer(key, epayload);
> + prep->payload[0] = NULL;
> + return 0;
> +}
> +
> static void encrypted_rcu_free(struct rcu_head *rcu)
> {
> struct encrypted_key_payload *epayload;
> @@ -837,50 +863,15 @@ static void encrypted_rcu_free(struct rcu_head *rcu)
> */
> static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
> {
> - struct encrypted_key_payload *epayload = key->payload.data;
> - struct encrypted_key_payload *new_epayload;
> - char *buf;
> - char *new_master_desc = NULL;
> - const char *format = NULL;
> - size_t datalen = prep->datalen;
> - int ret = 0;
> -
> - if (datalen <= 0 || datalen > 32767 || !prep->data)
> - return -EINVAL;
> + struct encrypted_key_payload *old;
> + struct encrypted_key_payload *new = prep->payload[0];
>
> - buf = kmalloc(datalen + 1, GFP_KERNEL);
> - if (!buf)
> - return -ENOMEM;
> -
> - buf[datalen] = 0;
> - memcpy(buf, prep->data, datalen);
> - ret = datablob_parse(buf, &format, &new_master_desc, NULL, NULL);
> - if (ret < 0)
> - goto out;
> + old = rcu_dereference_protected(key->payload.rcudata, &key->sem);
>
> - ret = valid_master_desc(new_master_desc, epayload->master_desc);
> - if (ret < 0)
> - goto out;
> -
> - new_epayload = encrypted_key_alloc(key, epayload->format,
> - new_master_desc, epayload->datalen);
> - if (IS_ERR(new_epayload)) {
> - ret = PTR_ERR(new_epayload);
> - goto out;
> - }
> -
> - __ekey_init(new_epayload, epayload->format, new_master_desc,
> - epayload->datalen);
> -
> - memcpy(new_epayload->iv, epayload->iv, ivsize);
> - memcpy(new_epayload->payload_data, epayload->payload_data,
> - epayload->payload_datalen);
> -
> - rcu_assign_keypointer(key, new_epayload);
> - call_rcu(&epayload->rcu, encrypted_rcu_free);
> -out:
> - kfree(buf);
> - return ret;
> + rcu_assign_keypointer(key, new);
> + prep->payload[0] = NULL;
> + call_rcu(&old->rcu, encrypted_rcu_free);
> + return 0;
> }
>
> /*
> @@ -893,7 +884,7 @@ static long encrypted_control(struct key *key, char *command,
> struct encrypted_key_payload *epayload, *new_epayload;
> char *new_master_desc = NULL;
> const char *format = NULL;
> - size_t datalen;
> + size_t datalen, quotalen;
> int ret;
>
> if (memcmp(command, expected_command, sizeof(expected_command) - 1) != 0)
> @@ -917,7 +908,7 @@ static long encrypted_control(struct key *key, char *command,
> return ret;
> }
>
> - new_epayload = encrypted_key_alloc(key, epayload->format,
> + new_epayload = encrypted_key_alloc("alen, epayload->format,
> new_master_desc, epayload->datalen);
> if (IS_ERR(new_epayload)) {
> up_write(&key->sem);
> @@ -1023,6 +1014,8 @@ static void encrypted_destroy(struct key *key)
>
> struct key_type key_type_encrypted = {
> .name = "encrypted",
> + .preparse = encrypted_preparse,
> + .free_preparse = encrypted_free_preparse,
> .instantiate = encrypted_instantiate,
> .update = encrypted_update,
> .match = user_match,
>
> --
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