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

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Date:   Sat, 26 Oct 2019 12:40:23 -0700
From:   Joe Perches <joe@...ches.com>
To:     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>
Cc:     ast@...nel.org, daniel@...earbox.net, jakub.kicinski@...ronome.com,
        hawk@...nel.org, john.fastabend@...il.com, mkubecek@...e.cz,
        jiri@...lanox.com, pablo@...filter.org, f.fainelli@...il.com,
        maxime.chevallier@...tlin.com, lirongqing@...du.com,
        vivien.didelot@...il.com, linyunsheng@...wei.com,
        natechancellor@...il.com, arnd@...db.de, dan.carpenter@...cle.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, xue.zhihong@....com.cn, wang.yi59@....com.cn,
        jiang.xuexin@....com.cn
Subject: Re: [PATCH] net: Zeroing the structure ethtool_wolinfo in
 ethtool_get_wol()

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?

There are ~4000 structs in include/uapi and
there are ~3000 uses of copy_to_user in the tree.

$ git grep -P '\bstruct\s+\w+\s*{' include/uapi/ | cut -f2 -d" "|sort|uniq|wc -l
3785
$ git grep -w copy_to_user|wc -l
2854

A trivial grep and manual search using:

$ git grep -B20 -w copy_to_user | grep -A20 -P '\bstruct\s+\w+\s*=\s*{'

shows at least 1 (I didn't look very hard and stopped after finding 1):

   include/uapi/linux/utsname.h:struct oldold_utsname {
   include/uapi/linux/utsname.h-   char sysname[9];
   include/uapi/linux/utsname.h-   char nodename[9];
   include/uapi/linux/utsname.h-   char release[9];
   include/uapi/linux/utsname.h-   char version[9];
   include/uapi/linux/utsname.h-   char machine[9];
   include/uapi/linux/utsname.h-};

and 

   kernel/sys.c-	struct oldold_utsname tmp = {};
   kernel/sys.c-
   kernel/sys.c-	if (!name)
   kernel/sys.c-		return -EFAULT;
   kernel/sys.c-
   kernel/sys.c-	down_read(&uts_sem);
   kernel/sys.c-	memcpy(&tmp.sysname, &utsname()->sysname, __OLD_UTS_LEN);
   kernel/sys.c-	memcpy(&tmp.nodename, &utsname()->nodename, __OLD_UTS_LEN);
   kernel/sys.c-	memcpy(&tmp.release, &utsname()->release, __OLD_UTS_LEN);
   kernel/sys.c-	memcpy(&tmp.version, &utsname()->version, __OLD_UTS_LEN);
   kernel/sys.c-	memcpy(&tmp.machine, &utsname()->machine, __OLD_UTS_LEN);
   kernel/sys.c-	up_read(&uts_sem);
   kernel/sys.c:	if (copy_to_user(name, &tmp, sizeof(tmp)))

where there is likely 3 bytes of padding after 45 bytes of data
in the struct.