linux-kernel - Re: [PATCH 2/2] IMA: Add audit log for failure conditions

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Message-ID: <1591993431.11061.116.camel@linux.ibm.com>
Date:   Fri, 12 Jun 2020 16:23:51 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        sgrubb@...hat.com, paul@...l-moore.com
Cc:     rgb@...hat.com, linux-integrity@...r.kernel.org,
        linux-audit@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] IMA: Add audit log for failure conditions

Hi Lakshmi,

I haven't yet tested the patch.  Below are a couple of comments.

On Wed, 2020-06-10 at 17:04 -0700, Lakshmi Ramasubramanian wrote:
> The final log statement in process_buffer_measurement() for failure
> condition is at debug level. This does not log the message unless
> the system log level is raised which would significantly increase
> the messages in the system log. Change this to an audit message to
> audit integrity failures with the "op" field of the audit message
> set to indicate the measurement operation that failed.

The problem with the existing "pr" level is kind of irrelevant.   You
could keep the existing pr_debug() statement, if you wanted to.  The
reason for auditing a failure is because it is "integrity" relevant or
more generically "security" relevant.  The first patch addresses the
change in the audit message format.

> 
> Also, add an audit message for failures in ima_alloc_key_entry().
> 
> Sample audit messages:
> 
> [    6.284329] audit: type=1804 audit(1591756723.627:2): pid=1 uid=0
> auid=4294967295 ses=4294967295 subj=kernel
> op=measuring_kexec_cmdline cause=alloc_entry errno=-12
> comm="swapper/0" name="kexec-cmdline" res=0
> 
> [    8.017126] audit: type=1804 audit(1591756725.360:10): pid=1
> uid=0 auid=4294967295 ses=4294967295
> subj=system_u:system_r:init_t:s0 op=measuring_key
> cause=hashing_error errno=-22 comm="systemd"
> name=".builtin_trusted_keys" res=0
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
> Suggested-by: Mimi Zohar <zohar@...ux.ibm.com>
> ---
>  security/integrity/ima/ima.h            | 48 ++++++++++++++++---------
>  security/integrity/ima/ima_main.c       | 18 +++++++---
>  security/integrity/ima/ima_policy.c     |  2 +-
>  security/integrity/ima/ima_queue_keys.c |  5 +++
>  4 files changed, 51 insertions(+), 22 deletions(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index df93ac258e01..e42101eebd69 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -186,27 +186,43 @@ static inline unsigned int ima_hash_key(u8 *digest)
>  	return (digest[0] | digest[1] << 8) % IMA_MEASURE_HTABLE_SIZE;
>  }
>  
> -#define __ima_hooks(hook)		\
> -	hook(NONE)			\
> -	hook(FILE_CHECK)		\
> -	hook(MMAP_CHECK)		\
> -	hook(BPRM_CHECK)		\
> -	hook(CREDS_CHECK)		\
> -	hook(POST_SETATTR)		\
> -	hook(MODULE_CHECK)		\
> -	hook(FIRMWARE_CHECK)		\
> -	hook(KEXEC_KERNEL_CHECK)	\
> -	hook(KEXEC_INITRAMFS_CHECK)	\
> -	hook(POLICY_CHECK)		\
> -	hook(KEXEC_CMDLINE)		\
> -	hook(KEY_CHECK)			\
> -	hook(MAX_CHECK)
> -#define __ima_hook_enumify(ENUM)	ENUM,
> +#define __ima_hooks(hook)				\
> +	hook(NONE, none)				\
> +	hook(FILE_CHECK, file)				\
> +	hook(MMAP_CHECK, mmap)				\
> +	hook(BPRM_CHECK, bprm)				\
> +	hook(CREDS_CHECK, creds)			\
> +	hook(POST_SETATTR, post_setattr)		\
> +	hook(MODULE_CHECK, module)			\
> +	hook(FIRMWARE_CHECK, firmware)			\
> +	hook(KEXEC_KERNEL_CHECK, kexec_kernel)		\
> +	hook(KEXEC_INITRAMFS_CHECK, kexec_initramfs)	\
> +	hook(POLICY_CHECK, policy)			\
> +	hook(KEXEC_CMDLINE, kexec_cmdline)		\
> +	hook(KEY_CHECK, key)				\
> +	hook(MAX_CHECK, none)
> +
> +#define __ima_hook_enumify(ENUM, str)	ENUM,
> +#define __ima_stringify(arg) (#arg)
> +#define __ima_hook_measuring_stringify(ENUM, str) \
> +		(__ima_stringify(measuring_ ##str)),
>  
>  enum ima_hooks {
>  	__ima_hooks(__ima_hook_enumify)
>  };
>  
> +static const char * const ima_hooks_measure_str[] = {
> +	__ima_hooks(__ima_hook_measuring_stringify)
> +};
> +
> +static inline const char *ima_hooks_func_measure_str(enum ima_hooks func)

"ima_hooks_func_measure_str" is a bit long.  There's no reason for
having both "hooks" and "func" in the name.  Also this is a static
function, so it doesn't really need to be prefixed with "ima_".  Maybe
truncate it to "func_measure_str()", similar to "func_token".

Mimi

> +{
> +	if (func >= MAX_CHECK)
> +		return ima_hooks_measure_str[NONE];
> +
> +	return ima_hooks_measure_str[func];
> +}
> +
>  extern const char *const func_tokens[];