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Subject: Re: [PATCH V4 2/2] EVM: Allow runtime modification of the set of
 verified xattrs
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Matthew Garrett <mjg59@google.com>, linux-integrity@vger.kernel.org
Date: Fri, 11 May 2018 12:58:23 -0400
In-Reply-To: <20180509202811.29875-2-mjg59@google.com>
References: <20180509202811.29875-1-mjg59@google.com>
         <20180509202811.29875-2-mjg59@google.com>
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On Wed, 2018-05-09 at 13:28 -0700, Matthew Garrett wrote:

> +/**
> + * evm_write_xattrs - write() for <securityfs>/evm_xattrs
> + * @file: file pointer, not actually used
> + * @buf: where to get the data from
> + * @count: bytes sent
> + * @ppos: where to start
> + *
> + * Returns number of bytes written or error code, as appropriate
> + */
> +static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
> +				size_t count, loff_t *ppos)
> +{
> +	int len, err;
> +	struct xattr_list *xattr, *tmp;
> +
> +	if (!capable(CAP_SYS_ADMIN) || evm_xattrs_locked)
> +		return -EPERM;
> +
> +	if (*ppos != 0)
> +		return -EINVAL;
> +
> +	if (count > XATTR_NAME_MAX)
> +		return -E2BIG;
> +
> +	xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL);
> +	if (!xattr)
> +		return -ENOMEM;
> +
> +	xattr->name = memdup_user_nul(buf, count);
> +	if (IS_ERR(xattr->name)) {
> +		err = PTR_ERR(xattr->name);
> +		kfree(xattr);
> +		return err;
> +	}
> +
> +	/* Remove any trailing newline */
> +	len = strlen(xattr->name);
> +	if (xattr->name[len-1] == '\n')
> +		xattr->name[len-1] = '\0';
> +
> +	if (strcmp(xattr->name, ".") == 0) {
> +		evm_xattrs_locked = 1;
> +		err = count;
> +		goto out;
> +	}
> +
> +	/* Guard against races in evm_read_xattrs */
> +	mutex_lock(&xattr_list_mutex);
> +	list_for_each_entry(tmp, &evm_config_xattrnames, list) {
> +		if (strcmp(xattr->name, tmp->name) == 0) {
> +			err = -EEXIST;
> +			mutex_unlock(&xattr_list_mutex);
> +			goto out;
> +		}
> +	}
> +	list_add_tail_rcu(&xattr->list, &evm_config_xattrnames);
> +	mutex_unlock(&xattr_list_mutex);
> +
> +	return count;
> +out:
> +	kfree(xattr->name);
> +	kfree(xattr);
> +	return err;
> +}

Shouldn't new xattrs be audited/logged?

Mimi