linux-kernel - Re: [RFC][PATCH 4/7] smack: fix label check in smack_kernel_act

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Date:	Wed, 27 Apr 2011 16:22:34 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Roberto Sassu <roberto.sassu@...ito.it>
CC:	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	dhowells@...hat.com, jmorris@...ei.org, zohar@...ux.vnet.ibm.com,
	safford@...son.ibm.com, tyhicks@...ux.vnet.ibm.com,
	kirkland@...onical.com, ecryptfs-devel@...ts.launchpad.net,
	eparis@...hat.com, sds@...ho.nsa.gov, selinux@...ho.nsa.gov,
	viro@...iv.linux.org.uk
Subject: Re: [RFC][PATCH 4/7] smack: fix label check in smack_kernel_act_as()

On 4/27/2011 5:34 AM, Roberto Sassu wrote:
> The function smack_kernel_act_as() must return -EINVAL if the label
> returned by smack_from_secid() is equal to 'smack_known_invalid.smk_known',
> which means that no entries in the 'smack_known_list' list matching the
> security identifier given are found.

I'll admit that the code here is wrong, but I disagree with the fix.

smack_from_secid() will never return NULL, so the check for NULL is
pointless. Checking for known_invalid is not right either, as the
Smack philosophy is to return a label in all cases, as is evident
by the behavior of smack_from_secid(). Thus, the correct change
would be to remove the error check completely and set the new task
value to the value obtained from smack_from_secid in all cases.

Besides, where did the caller of this function get a secid that isn't
going to map to a Smack label?

> Signed-off-by: Roberto Sassu <roberto.sassu@...ito.it>
> ---
>  security/smack/smack_lsm.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index e3c9e54..0e7ed31 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -1415,7 +1415,7 @@ static int smack_kernel_act_as(struct cred *new, u32 secid)
>  	struct task_smack *new_tsp = new->security;
>  	char *smack = smack_from_secid(secid);
>  
> -	if (smack == NULL)
> +	if (smack == smack_known_invalid.smk_known)
>  		return -EINVAL;
>  
>  	new_tsp->smk_task = smack;

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