linux-kernel - Re: [Cocci] [PATCH] net: Zeroing the structure ethtool_wolinfo in ethtool_get

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Message-ID: <20191121120733.GF5604@kadam>
Date:   Thu, 21 Nov 2019 15:07:33 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Joe Perches <joe@...ches.com>,
        zhanglin <zhang.lin16@....com.cn>, davem@...emloft.net,
        cocci <cocci@...teme.lip6.fr>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        jakub.kicinski@...ronome.com, ast@...nel.org,
        jiang.xuexin@....com.cn, f.fainelli@...il.com,
        daniel@...earbox.net, john.fastabend@...il.com,
        lirongqing@...du.com, maxime.chevallier@...tlin.com,
        vivien.didelot@...il.com, wang.yi59@....com.cn, hawk@...nel.org,
        arnd@...db.de, jiri@...lanox.com, xue.zhihong@....com.cn,
        natechancellor@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linyunsheng@...wei.com,
        pablo@...filter.org, bpf@...r.kernel.org
Subject: Re: [Cocci] [PATCH] net: Zeroing the structure ethtool_wolinfo in
 ethtool_get_wol()

On Thu, Nov 21, 2019 at 12:19:17PM +0100, Michal Kubecek wrote:
> On Thu, Nov 21, 2019 at 11:23:34AM +0100, Enrico Weigelt, metux IT consult wrote:
> > On 26.10.19 21:40, Joe Perches wrote:
> > > On Sat, 2019-10-26 at 15:54 +0800, zhanglin wrote:
> > >> memset() the structure ethtool_wolinfo that has padded bytes
> > >> but the padded bytes have not been zeroed out.
> > > []
> > >> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> > > []
> > >> @@ -1471,11 +1471,13 @@ static int ethtool_reset(struct net_device *dev, char __user *useraddr)
> > >>  
> > >>  static int ethtool_get_wol(struct net_device *dev, char __user *useraddr)
> > >>  {
> > >> -	struct ethtool_wolinfo wol = { .cmd = ETHTOOL_GWOL };
> > >> +	struct ethtool_wolinfo wol;
> > >>  
> > >>  	if (!dev->ethtool_ops->get_wol)
> > >>  		return -EOPNOTSUPP;
> > >>  
> > >> +	memset(&wol, 0, sizeof(struct ethtool_wolinfo));
> > >> +	wol.cmd = ETHTOOL_GWOL;
> > >>  	dev->ethtool_ops->get_wol(dev, &wol);
> > >>  
> > >>  	if (copy_to_user(useraddr, &wol, sizeof(wol)))
> > > 
> > > It seems likely there are more of these.
> > > 
> > > Is there any way for coccinelle to find them?
> > 
> > Just curios: is static struct initialization (on stack) something that
> > should be avoided ? I've been under the impression that static
> > initialization allows thinner code and gives the compiler better chance
> > for optimizations.
> 
> Not in general. The (potential) problem here is that the structure has
> padding and it is as a whole (i.e. including the padding) copied to
> userspace. While I'm not aware of a compiler that wouldn't actually
> initialize the whole data block including the padding in this case, the
> C standard provides no guarantee about that so that to be sure we cannot
> leak leftover kernel data to userspace, we need to explicitly initialize
> the whole block.

GCC will not always initialize the struct holes.  This patch fixes a
real bug that GCC on my system (v7.4)

regards,
dan carpenter