linux-kernel - Re: [PATCHv3 3/6] evm: enable EVM when X509 certificate is loaded

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Date:	Mon, 26 Oct 2015 21:18:24 +0200
From:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	linux-ima-devel <linux-ima-devel@...ts.sourceforge.net>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Kasatkin <dmitry.kasatkin@...wei.com>
Subject: Re: [PATCHv3 3/6] evm: enable EVM when X509 certificate is loaded

Hi,

I added error printing to the patch

http://git.kernel.org/cgit/linux/kernel/git/kasatkin/linux-digsig.git/log/?h=ima-next

Dmitry


On Fri, Oct 23, 2015 at 9:31 PM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> On Thu, 2015-10-22 at 21:49 +0300, Dmitry Kasatkin wrote:
>> In order to enable EVM before starting 'init' process,
>> evm_initialized needs to be non-zero. Before it was
>> indicating that HMAC key is loaded. When EVM loads
>> X509 before calling 'init', it is possible to enable
>> EVM to start signature based verification.
>>
>> This patch defines bits to enable EVM if key of any type
>> is loaded.
>
> Thanks, Dmitry.  There's one comment inline.
>
>> Changes in v2:
>> * EVM_STATE_KEY_SET replaced by EVM_INIT_HMAC
>> * EVM_STATE_X509_SET replaced by EVM_INIT_X509
>>
>> Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@...wei.com>
>> ---
>>  security/integrity/evm/evm.h        | 3 +++
>>  security/integrity/evm/evm_crypto.c | 2 ++
>>  security/integrity/evm/evm_main.c   | 6 +++++-
>>  security/integrity/evm/evm_secfs.c  | 4 ++--
>>  4 files changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
>> index 88bfe77..f5f1272 100644
>> --- a/security/integrity/evm/evm.h
>> +++ b/security/integrity/evm/evm.h
>> @@ -21,6 +21,9 @@
>>
>>  #include "../integrity.h"
>>
>> +#define EVM_INIT_HMAC        0x0001
>> +#define EVM_INIT_X509        0x0002
>> +
>>  extern int evm_initialized;
>>  extern char *evm_hmac;
>>  extern char *evm_hash;
>> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
>> index 159ef3e..34e1a6f 100644
>> --- a/security/integrity/evm/evm_crypto.c
>> +++ b/security/integrity/evm/evm_crypto.c
>> @@ -40,6 +40,8 @@ static struct shash_desc *init_desc(char type)
>>       struct shash_desc *desc;
>>
>>       if (type == EVM_XATTR_HMAC) {
>> +             if (!(evm_initialized & EVM_INIT_HMAC))
>> +                     return ERR_PTR(-ENOKEY);
>
> init_desc() is called from a couple of different places.  In some
> instances, like when converting from a signature to an hmac, if
> init_desc() fails, the xattr isn't converted to an HMAC.  No big deal.
> But there are other cases, like when a protected xattr is modified,
> failing the write will make the file inaccessible.  Does there need to
> be an error msg of some sort or an audit msg?
>
> Mimi
>
>>               tfm = &hmac_tfm;
>>               algo = evm_hmac;
>>       } else {
>> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
>> index 519de0a..420d94d 100644
>> --- a/security/integrity/evm/evm_main.c
>> +++ b/security/integrity/evm/evm_main.c
>> @@ -475,7 +475,11 @@ EXPORT_SYMBOL_GPL(evm_inode_init_security);
>>  #ifdef CONFIG_EVM_LOAD_X509
>>  void __init evm_load_x509(void)
>>  {
>> -     integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
>> +     int rc;
>> +
>> +     rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
>> +     if (!rc)
>> +             evm_initialized |= EVM_INIT_X509;
>>  }
>>  #endif
>>
>> diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
>> index cf12a04..3f775df 100644
>> --- a/security/integrity/evm/evm_secfs.c
>> +++ b/security/integrity/evm/evm_secfs.c
>> @@ -64,7 +64,7 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
>>       char temp[80];
>>       int i, error;
>>
>> -     if (!capable(CAP_SYS_ADMIN) || evm_initialized)
>> +     if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_INIT_HMAC))
>>               return -EPERM;
>>
>>       if (count >= sizeof(temp) || count == 0)
>> @@ -80,7 +80,7 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
>>
>>       error = evm_init_key();
>>       if (!error) {
>> -             evm_initialized = 1;
>> +             evm_initialized |= EVM_INIT_HMAC;
>>               pr_info("initialized\n");
>>       } else
>>               pr_err("initialization failed\n");
>
>



-- 
Thanks,
Dmitry
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