linux-kernel - Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

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Date:   Tue, 1 Aug 2017 16:33:50 -0500
From:   Gary R Hook <gary.hook@....com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

On 08/01/2017 03:35 PM, Arnd Bergmann wrote:
> On Tue, Aug 1, 2017 at 4:52 PM, Gary R Hook <gary.hook@....com> wrote:
>> On 07/31/2017 03:49 PM, Arnd Bergmann wrote:
>>>
>>> The added support for version 5 CCPs introduced a false-positive
>>> warning in the RSA implementation:
>>>
>>> drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
>>> drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used
>>> uninitialized in this function [-Werror=maybe-uninitialized]
>>>
>>> This changes the code in a way that should make it easier for
>>> the compiler to track the state of the sb_count variable, and
>>> avoid the warning.
>>>
>>> Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5
>>> CCPs")
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>> ---
>>>  drivers/crypto/ccp/ccp-ops.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
>>> index 40c062ad8726..a8bc207b099a 100644
>>> --- a/drivers/crypto/ccp/ccp-ops.c
>>> +++ b/drivers/crypto/ccp/ccp-ops.c
>>> @@ -1758,6 +1758,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
>>> *cmd_q, struct ccp_cmd *cmd)
>>>         o_len = 32 * ((rsa->key_size + 255) / 256);
>>>         i_len = o_len * 2;
>>>
>>> +       sb_count = 0;
>>>         if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
>>>                 /* sb_count is the number of storage block slots required
>>>                  * for the modulus.
>>> @@ -1852,7 +1853,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
>>> *cmd_q, struct ccp_cmd *cmd)
>>>         ccp_dm_free(&exp);
>>>
>>>  e_sb:
>>> -       if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
>>> +       if (sb_count)
>>>                 cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key,
>>> sb_count);
>>>
>>>         return ret;
>>>
>>
>> This is a fine solution. However, having lived with this annoyance for a
>> while, and even hoping that a
>> a later compiler fixes it, I would have preferred to either:
>>
>> 1) Initialize the local variable at declaration time, or
>
> I try to never do that in general, see https://rusty.ozlabs.org/?p=232

I know. I just globally disagree with a global decision of this sort.
Now I make errors that are more complex, partially because I've shot myself
in the foot repeatedly, and learned from it.

Nonetheless...

I will ack your suggested patch. Thank you for addressing this. I've learned
something.