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

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Date:	Mon, 09 Jun 2014 11:17:08 +0300
From:	Dmitry Kasatkin <d.kasatkin@...sung.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:	linux-security-module <linux-security-module@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Josh Boyer <jwboyer@...hat.com>,
	keyrings <keyrings@...ux-nfs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 1/4] KEYS: special dot prefixed keyring name bug fix

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@...ux.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@...sung.com>
>>>> Cc: David Howells <dhowells@...hat.com>
>>>> Signed-off-by: Mimi Zohar <zohar@...ux.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
>>
>>
>>

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