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SubjectRe: [RFC v2 1/7] integrity: added digest calculation function
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On Thu, Aug 16, 2012 at 12:11 AM, Kasatkin, Dmitry
<dmitry.kasatkin@intel.com> wrote:
> On Wed, Aug 15, 2012 at 11:11 PM, Serge Hallyn
> <serge.hallyn@canonical.com> wrote:
>> Quoting Dmitry Kasatkin (dmitry.kasatkin@intel.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@intel.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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