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

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Date:   Tue, 3 Oct 2023 16:28:19 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Casey Schaufler <casey@...aufler-ca.com>
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
Subject: Re: [PATCH v15 08/11] Smack: implement setselfattr and getselfattr
 hooks

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.

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