linux-kernel - Re: [RFC v2 1/7] integrity: added digest calculation function

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Date:	Thu, 16 Aug 2012 23:32:03 +0300
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	Serge Hallyn <serge.hallyn@...onical.com>
Cc:	zohar@...ux.vnet.ibm.com, jmorris@...ei.org, rusty@...tcorp.com.au,
	dhowells@...hat.com, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 1/7] integrity: added digest calculation function

On Thu, Aug 16, 2012 at 12:11 AM, Kasatkin, Dmitry
<dmitry.kasatkin@...el.com> wrote:
> On Wed, Aug 15, 2012 at 11:11 PM, Serge Hallyn
> <serge.hallyn@...onical.com> wrote:
>> Quoting Dmitry Kasatkin (dmitry.kasatkin@...el.com):
>>> There are several functions, that need to calculate digest.
>>> This patch adds common function for use by integrity subsystem.
>>>
>>> Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@...el.com>
>>> ---
>>>  security/integrity/digsig.c    |   31 +++++++++++++++++++++++++++++--
>>>  security/integrity/integrity.h |    3 +++
>>>  2 files changed, 32 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
>>> index 2dc167d..61a0c92 100644
>>> --- a/security/integrity/digsig.c
>>> +++ b/security/integrity/digsig.c
>>> @@ -13,9 +13,9 @@
>>>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>>>
>>>  #include <linux/err.h>
>>> -#include <linux/rbtree.h>
>>>  #include <linux/key-type.h>
>>>  #include <linux/digsig.h>
>>> +#include <crypto/hash.h>
>>>
>>>  #include "integrity.h"
>>>
>>> @@ -28,7 +28,7 @@ static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
>>>  };
>>>
>>>  int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
>>> -                                     const char *digest, int digestlen)
>>> +                         const char *digest, int digestlen)
>>>  {
>>>       if (id >= INTEGRITY_KEYRING_MAX)
>>>               return -EINVAL;
>>> @@ -46,3 +46,30 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
>>>
>>>       return digsig_verify(keyring[id], sig, siglen, digest, digestlen);
>>>  }
>>> +
>>> +int integrity_calc_digest(const char *algo, const void *data, const int len,
>>> +                       char *digest)
>>> +{
>>> +     int rc = -ENOMEM;
>>> +     struct crypto_shash *tfm;
>>> +
>>> +     tfm = crypto_alloc_shash(algo, 0, 0);
>>> +     if (IS_ERR(tfm)) {
>>> +             rc = PTR_ERR(tfm);
>>> +             pr_err("Can not allocate %s (reason: %d)\n", algo, rc);
>>> +             return rc;
>>> +     } else {
>>> +             struct {
>>> +                     struct shash_desc shash;
>>> +                     char ctx[crypto_shash_descsize(tfm)];
>>> +             } desc;
>>
>> Needless confusing indentation here.  Just move the struct {} desc; to the
>> top and drop the else.  That will make it much more readable.
>>
>
> Intention was to allocate it only if tfm allocation succeeded..
> But indeed failure very unlikely..
>

BTW.. The reason for such code is that ctx member uses function in the
parameter:

char ctx[crypto_shash_descsize(tfm)];

It is not possible to do it before tfm allocation...
So I cannot move it up..
I can only kmalloc it then.

There are many places of such allocation on stack in the kernel code.
sparse also complains. I know..
But it looks for me reasonable, as descriptor size is not big...

- Dmitry

> thanks.
>
>>> +             desc.shash.tfm = tfm;
>>> +             desc.shash.flags = 0;
>>> +
>>> +             rc = crypto_shash_digest(&desc.shash, data, len, digest);
>>> +     }
>>> +
>>> +     crypto_free_shash(tfm);
>>> +     return rc;
>>> +}
>>> diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
>>> index e21362a..48ee2d4 100644
>>> --- a/security/integrity/integrity.h
>>> +++ b/security/integrity/integrity.h
>>> @@ -59,6 +59,9 @@ struct integrity_iint_cache *integrity_iint_find(struct inode *inode);
>>>
>>>  #ifdef CONFIG_INTEGRITY_SIGNATURE
>>>
>>> +int integrity_calc_digest(const char *algo, const void *data, const int len,
>>> +                       char *digest);
>>> +
>>>  int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
>>>                                       const char *digest, int digestlen);
>>>
>>> --
>>> 1.7.9.5
>>>
>>> --
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