Re: [PATCH -next,v2] gss_krb5: refactor code to return correct PTR_ERR in krb5_DK

[cuigaosheng <cuigaosheng1@huawei.com>]

But crypto_sync_skcipher_setkey maybe return -ENOMEM, Should this be 
modified?

thanks!

On 2024/7/15 0:18, Chuck Lever III wrote:
>
>> On Jul 14, 2024, at 12:31 AM, NeilBrown <neilb@suse.de> wrote:
>>
>> On Sat, 13 Jul 2024, Chuck Lever wrote:
>>> On Fri, Jul 12, 2024 at 09:39:08AM -0400, Chuck Lever wrote:
>>>> On Fri, Jul 12, 2024 at 03:24:23PM +0800, Gaosheng Cui wrote:
>>>>> Refactor the code in krb5_DK to return PTR_ERR when an error occurs.
>>>> My understanding of the current code is that if either
>>>> crypto_alloc_sync_skcipher() or crypto_sync_skcipher_blocksize()
>>>> fails, then krb5_DK() returns -EINVAL. At the only call site for
>>>> krb5_DK(), that return code is unconditionally discarded. Thus I
>>>> don't see that the proposed change is necessary or improves
>>>> anything.
>>> My understanding is wrong  ;-)
>> True, but I think your conclusion was correct.
>>
>> krb5_DK() returns zero or -EINVAL.
>> It is only used by krb5_derive_key_v2(), which returns zero or -EINVAL,
>> or -ENOMEM.
> These are really the only three interesting return codes.
> Leaking other error codes to callers is not desirable, IMO.
>
> But looking at the current implementation of
> crypto_alloc_sync_skcipher(), it returns either
> ERR_PTR(-EINVAL) or a valid pointer; it doesn't return any
> other error value. Since it never returns -ENOMEM, there
> still doesn't seem to be a technical reason for modifying
> krb5_DK() to pass errors through.
>
>
>> krb4_derive_key_v2() is only used as a ->derive_key() method.
>> This is called from krb5_derive_key(), and various unit tests in
>> gss_krb5_tests.c
>>
>> krb5_derive_key() is only called in gss_krb5_mech.c, and each call site
>> is of the form:
>>   if (krb5_derive_key(...)) goto out;
>> so it doesn't matter what error is returned.
>>
>> The unit test calls are all followed by
>> KUNIT_ASSERT_EQ(test, err, 0);
>> so the only place the err is used is (presumably) in failure reports
>> from the unit tests.
>>
>> So the proposed change seems unnecessary from a practical perspective.
>>
>> Maybe it is justified from an aesthetic perspective, but I think that
>> should be clearly stated in the commit message.  e.g.
>>
>>   This change has no practical effect as all non-zero error statuses
>>   are treated equally, however the distinction between EINVAL and ENOMEM
>>   may be relevant at some future time and it seems cleaner to maintain
>>   the distinction.
>>
>> NeilBrown
>>
>>
>>> The return code isn't discarded. A non-zero return code from
>>> krb5_DK() is carried back up the call stack. The logic in
>>> krb5_derive_key_v2() does not use the kernel's usual error flow
>>> form, so I missed this.
>>>
>>> However, it still isn't clear to me why the error behavior here
>>> needs to change. It's possible, for example, that -EINVAL is
>>> perfectly adequate to indicate when sync_skcipher() can't find the
>>> specified encryption algorithm (gk5e->encrypt_name).
>>>
>>> Specifying the wrong encryption type: -EINVAL. That makes sense.
>>>
>>>
>>>>> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
>>>>> ---
>>>>> v2: Update IS_ERR to PTR_ERR, thanks very much!
>>>>> net/sunrpc/auth_gss/gss_krb5_keys.c | 8 ++++++--
>>>>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/net/sunrpc/auth_gss/gss_krb5_keys.c b/net/sunrpc/auth_gss/gss_krb5_keys.c
>>>>> index 4eb19c3a54c7..5ac8d06ab2c0 100644
>>>>> --- a/net/sunrpc/auth_gss/gss_krb5_keys.c
>>>>> +++ b/net/sunrpc/auth_gss/gss_krb5_keys.c
>>>>> @@ -164,10 +164,14 @@ static int krb5_DK(const struct gss_krb5_enctype *gk5e,
>>>>> goto err_return;
>>>>>
>>>>> cipher = crypto_alloc_sync_skcipher(gk5e->encrypt_name, 0, 0);
>>>>> - if (IS_ERR(cipher))
>>>>> + if (IS_ERR(cipher)) {
>>>>> + ret = PTR_ERR(cipher);
>>>>> goto err_return;
>>>>> + }
>>>>> +
>>>>> blocksize = crypto_sync_skcipher_blocksize(cipher);
>>>>> - if (crypto_sync_skcipher_setkey(cipher, inkey->data, inkey->len))
>>>>> + ret = crypto_sync_skcipher_setkey(cipher, inkey->data, inkey->len);
>>>>> + if (ret)
>>>>> goto err_free_cipher;
>>>>>
>>>>> ret = -ENOMEM;
>>>>> -- 
>>>>> 2.25.1
>>>>>
>>>> -- 
>>>> Chuck Lever
>>>>
>>> -- 
>>> Chuck Lever
>>>
> --
> Chuck Lever
>
>