Re: [RFC PATCH v5 1/4] KEYS: special dot prefixed keyring name bug fix

Dmitry Kasatkin
2014-06-09T08:17:34Z

On 09/06/14 10:56, Dmitry Kasatkin wrote:
> On 07/06/14 01:00, Mimi Zohar wrote:
>> On Sat, 2014-06-07 at 00:48 +0300, Dmitry Kasatkin wrote:
>>> On 3 June 2014 20:58, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
>>>> Dot prefixed keyring names are supposed to be reserved for the
>>>> kernel, but add_key() calls key_get_type_from_user(), which
>>>> incorrectly verifies the 'type' field, not the 'description' field.
>>>> This patch verifies the 'description' field isn't dot prefixed,
>>>> when creating a new keyring, and removes the dot prefix test in
>>>> key_get_type_from_user().
>>>>
>>>> Changelog v5:
>>>> - Only prevent userspace from creating a dot prefixed keyring, not
>>>> regular keys - Dmitry
>>>>
>>>> Reported-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
>>>> Cc: David Howells <dhowells@redhat.com>
>>>> Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
>>>> ---
>>>> security/keys/keyctl.c | 6 ++++--
>>>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
>>>> index cd5bd0c..62a9952 100644
>>>> --- a/security/keys/keyctl.c
>>>> +++ b/security/keys/keyctl.c
>>>> @@ -37,8 +37,6 @@ static int key_get_type_from_user(char *type,
>>>> return ret;
>>>> if (ret == 0 || ret >= len)
>>>> return -EINVAL;
>>>> - if (type[0] == '.')
>>>> - return -EPERM;
>>>> type[len - 1] = '\0';
>>>> return 0;
>>>> }
>>>> @@ -86,6 +84,10 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
>>>> if (!*description) {
>>>> kfree(description);
>>>> description = NULL;
>>>> + } else if ((description[0] == '.') &&
>>>> + (strncmp(type, "keyring", 7) == 0)) {

BTW. using strcmp is good enough here. string constants are always NULL
terminated.
Comparison will terminate after no more than 7 bytes.

>>>> + ret = -EPERM;
>>>> + goto error2;
>>>> }
>>>> }
>>> I think it does not another problem...
>>> It is not only prevent creating new keyring with ".abc" name but also
>>> prevent adding new key...
>>>
>>> this is wrong...
>> Seems to prevent creating a dot prefixed keyring, but permits creating a
>> dot prefixed key. Do you have an example?
> I think by mistake I was checking old patch in the thread because I have
> not noticed strncmp(type, "keyring", 7).
> This patch definitely should do the job.
>
> - Dmitry
>
>
>> thanks,
>>
>> Mimi
>>
>> Mimi
>>
>>
>>