linux-hardening - Re: [PATCH v2] net: bonding: Use strscpy() instead of manually-truncated strncpy()

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Date:   Wed, 02 Jun 2021 13:47:20 -0700
From:   Jay Vosburgh <jay.vosburgh@...onical.com>
To:     Kees Cook <keescook@...omium.org>
cc:     kernel test robot <lkp@...el.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: Re: [PATCH v2] net: bonding: Use strscpy() instead of manually-truncated strncpy()

Kees Cook <keescook@...omium.org> wrote:

>Silence this warning by just 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
>Signed-off-by: Kees Cook <keescook@...omium.org>

	There's one more "strncpy(...); primary[IFNAMSIZ - 1] = 0;" set
in bond_options.c:bond_option_primary_set(), doesn't it also generate
this warning?

	Either way, the change looks good to me.

Acked-by: Jay Vosburgh <jay.vosburgh@...onical.com>

	-J


>---
>v2:
> - switch to strscpy_pad() and replace earlier strncpy() too
>v1: https://lore.kernel.org/lkml/20210602181133.3326856-1-keescook@chromium.org
>---
> drivers/net/bonding/bond_main.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 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));
> 
>-- 
>2.25.1

---
	-Jay Vosburgh, jay.vosburgh@...onical.com