linux-hardening - [PATCH v3] net: bonding: Use strscpy_pad() instead of manually-truncated strncpy()

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Date:   Wed,  2 Jun 2021 13:58:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     Kees Cook <keescook@...omium.org>,
        kernel test robot <lkp@...el.com>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v3] net: bonding: Use strscpy_pad() instead of manually-truncated strncpy()

Silence this warning by using strscpy_pad() directly:

drivers/net/bonding/bond_main.c:4877:3: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
    4877 |   strncpy(params->primary, primary, IFNAMSIZ);
         |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Additionally replace other strncpy() uses, as it is considered deprecated:
https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings

Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/202102150705.fdR6obB0-lkp@intel.com
Acked-by: Jay Vosburgh <jay.vosburgh@...onical.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
v3: - other files in drivers/net/bonding/ too!
v2: https://lore.kernel.org/lkml/20210602203138.4082470-1-keescook@chromium.org
v1: https://lore.kernel.org/lkml/20210602181133.3326856-1-keescook@chromium.org

---
 drivers/net/bonding/bond_main.c    | 8 +++-----
 drivers/net/bonding/bond_options.c | 3 +--
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index c5a646d06102..e9cb716ad849 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -620,7 +620,7 @@ static int bond_check_dev_link(struct bonding *bond,
 		 */
 
 		/* Yes, the mii is overlaid on the ifreq.ifr_ifru */
-		strncpy(ifr.ifr_name, slave_dev->name, IFNAMSIZ);
+		strscpy_pad(ifr.ifr_name, slave_dev->name, IFNAMSIZ);
 		mii = if_mii(&ifr);
 		if (ioctl(slave_dev, &ifr, SIOCGMIIPHY) == 0) {
 			mii->reg_num = MII_BMSR;
@@ -5329,10 +5329,8 @@ static int bond_check_params(struct bond_params *params)
 			(struct reciprocal_value) { 0 };
 	}
 
-	if (primary) {
-		strncpy(params->primary, primary, IFNAMSIZ);
-		params->primary[IFNAMSIZ - 1] = 0;
-	}
+	if (primary)
+		strscpy_pad(params->primary, primary, sizeof(params->primary));
 
 	memcpy(params->arp_targets, arp_target, sizeof(arp_target));
 
diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
index c9d3604ae129..81c039531e66 100644
--- a/drivers/net/bonding/bond_options.c
+++ b/drivers/net/bonding/bond_options.c
@@ -1206,8 +1206,7 @@ static int bond_option_primary_set(struct bonding *bond,
 		RCU_INIT_POINTER(bond->primary_slave, NULL);
 		bond_select_active_slave(bond);
 	}
-	strncpy(bond->params.primary, primary, IFNAMSIZ);
-	bond->params.primary[IFNAMSIZ - 1] = 0;
+	strscpy_pad(bond->params.primary, primary, IFNAMSIZ);
 
 	netdev_dbg(bond->dev, "Recording %s as primary, but it has not been enslaved yet\n",
 		   primary);
-- 
2.25.1