linux-kernel - Re: [PATCH v15 08/11] Smack: implement setselfattr and getselfattr hooks

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Message-ID: <8880b6e1-eae7-4317-b038-05aedcb41532@schaufler-ca.com>
Date:   Fri, 20 Oct 2023 12:42:43 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     paul@...l-moore.com, linux-security-module@...r.kernel.org,
        jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v15 08/11] Smack: implement setselfattr and getselfattr
 hooks

On 10/3/2023 7:28 AM, Mickaël Salaün wrote:
> On Tue, Sep 12, 2023 at 01:56:53PM -0700, Casey Schaufler wrote:
>> Implement Smack support for security_[gs]etselfattr.
>> Refactor the setprocattr hook to avoid code duplication.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> Reviewed-by: John Johansen <john.johansen@...onical.com>
>> ---
>>  security/smack/smack_lsm.c | 95 ++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 90 insertions(+), 5 deletions(-)
>>
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index f73f9a2834eb..12160d060cc1 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -3626,6 +3626,46 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>>  	return;
>>  }
>>  
>> +/**
>> + * smack_getselfattr - Smack current process attribute
>> + * @attr: which attribute to fetch
>> + * @ctx: buffer to receive the result
>> + * @size: available size in, actual size out
>> + * @flags: unused
>> + *
>> + * Fill the passed user space @ctx with the details of the requested
>> + * attribute.
>> + *
>> + * Returns the number of attributes on success, an error code otherwise.
>> + * There will only ever be one attribute.
>> + */
>> +static int smack_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
>> +			     size_t *size, u32 flags)
>> +{
>> +	struct smack_known *skp = smk_of_current();
>> +	int total;
>> +	int slen;
>> +	int rc;
>> +
>> +	if (attr != LSM_ATTR_CURRENT)
>> +		return -EOPNOTSUPP;
>> +
>> +	slen = strlen(skp->smk_known) + 1;
>
>> +	total = ALIGN(slen + sizeof(*ctx), 8);
>> +	if (total > *size)
>> +		rc = -E2BIG;
>> +	else if (ctx)
>> +		rc = lsm_fill_user_ctx(ctx, skp->smk_known, slen, LSM_ID_SMACK,
>> +				       0);
>> +	else
>> +		rc = 1;
> Can we move these checks into lsm_fill_user_ctx()? They are similar for
> AppArmor and SELinux.

Possibly, but that would make lsm_fill_user_ctx() into lsm_validiate_and_fill_user_ctx(),
and I don't want to do that.

>
>> +
>> +	*size = total;
>> +	if (rc >= 0)
>> +		return 1;
>> +	return rc;
>> +}