From: Harald Freudenberger Subject: [PATCH 2/2] crypto: hwrng remember rng chosen by user Date: Tue, 11 Jul 2017 09:36:23 +0200 Message-ID: <1499758583-14626-3-git-send-email-freude@linux.vnet.ibm.com> References: <1499758583-14626-1-git-send-email-freude@linux.vnet.ibm.com> Cc: herbert@gondor.apana.org.au, arnd@arndb.de, gregkh@linuxfoundation.org, prasannatsmkumar@gmail.com, schwidefsky@de.ibm.com, Harald Freudenberger To: linux-crypto@vger.kernel.org Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45580 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755382AbdGKHhY (ORCPT ); Tue, 11 Jul 2017 03:37:24 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v6B7YOOO047348 for ; Tue, 11 Jul 2017 03:37:18 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0b-001b2d01.pphosted.com with ESMTP id 2bmd4c12b2-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 11 Jul 2017 03:37:18 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 11 Jul 2017 08:37:16 +0100 In-Reply-To: <1499758583-14626-1-git-send-email-freude@linux.vnet.ibm.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: When a user chooses a rng source via sysfs attribute this rng should be sticky, even when other sources with better quality to register. This patch introduces a simple way to remember the user's choice. This is reflected by a new sysfs attribute file 'rng_selected' which shows if the current rng has been chosen by userspace. The new attribute file shows '1' for user selected rng and '0' otherwise. Signed-off-by: Harald Freudenberger Reviewed-by: PrasannaKumar Muralidharan --- drivers/char/hw_random/core.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index e9dda16..9701ac7 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -28,6 +28,8 @@ #define RNG_MODULE_NAME "hw_random" static struct hwrng *current_rng; +/* the current rng has been explicitly chosen by user via sysfs */ +static int cur_rng_set_by_user; static struct task_struct *hwrng_fill; /* list of registered rngs, sorted decending by quality */ static LIST_HEAD(rng_list); @@ -304,6 +306,7 @@ static ssize_t hwrng_attr_current_store(struct device *dev, list_for_each_entry(rng, &rng_list, list) { if (sysfs_streq(rng->name, buf)) { err = 0; + cur_rng_set_by_user = 1; if (rng != current_rng) err = set_current_rng(rng); break; @@ -352,16 +355,27 @@ static ssize_t hwrng_attr_available_show(struct device *dev, return strlen(buf); } +static ssize_t hwrng_attr_selected_show(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user); +} + static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR, hwrng_attr_current_show, hwrng_attr_current_store); static DEVICE_ATTR(rng_available, S_IRUGO, hwrng_attr_available_show, NULL); +static DEVICE_ATTR(rng_selected, S_IRUGO, + hwrng_attr_selected_show, + NULL); static struct attribute *rng_dev_attrs[] = { &dev_attr_rng_current.attr, &dev_attr_rng_available.attr, + &dev_attr_rng_selected.attr, NULL }; @@ -444,10 +458,12 @@ int hwrng_register(struct hwrng *rng) old_rng = current_rng; err = 0; - if (!old_rng || (rng->quality > old_rng->quality)) { + if (!old_rng || + (!cur_rng_set_by_user && rng->quality > old_rng->quality)) { /* * Set new rng as current as the new rng source - * provides better entropy quality. + * provides better entropy quality and was not + * chosen by userspace. */ err = set_current_rng(rng); if (err) @@ -479,6 +495,7 @@ void hwrng_unregister(struct hwrng *rng) list_del(&rng->list); if (current_rng == rng) { drop_current_rng(); + cur_rng_set_by_user = 0; /* rng_list is sorted by quality, use the best (=first) one */ if (!list_empty(&rng_list)) { struct hwrng *new_rng; -- 2.7.4