netdev - 答复: 答复: [PATCH] net: ethtool: not call vzalloc for zero sized memory request

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Message-ID: <260f8b4bfffc4a838683bc3906c1c799@baidu.com>
Date:   Thu, 28 Mar 2019 11:00:12 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     Michal Kubecek <mkubecek@...e.cz>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: 答复: 答复: [PATCH] net: ethtool: not call vzalloc for zero sized memory request



> -----邮件原件-----
> 发件人: Michal Kubecek [mailto:mkubecek@...e.cz]
> 发送时间: 2019年3月28日 18:26
> 收件人: Li,Rongqing <lirongqing@...du.com>
> 抄送: netdev@...r.kernel.org
> 主题: Re: 答复: [PATCH] net: ethtool: not call vzalloc for zero sized memory
> request
> 
> On Thu, Mar 28, 2019 at 09:51:56AM +0000, Li,Rongqing wrote:
> > > -----邮件原件-----
> > > 发件人: Michal Kubecek [mailto:mkubecek@...e.cz]
> > > 发送时间: 2019年3月28日 17:09
> > > 收件人: Li,Rongqing <lirongqing@...du.com>
> > > 抄送: netdev@...r.kernel.org
> > > 主题: Re: [PATCH] net: ethtool: not call vzalloc for zero sized memory
> > > request
> > >
> > > On Thu, Mar 28, 2019 at 02:01:09PM +0800, Li RongQing wrote:
> > > > NULL or ZERO_SIZE_PTR will be returned for zero sized memory
> > > > request, and derefencing them will lead to a segfault
> > > >
> > > > so it is unnecessory to call vzalloc for zero sized memory request
> > > > and not call __ethtool_get_strings which always uses the allocated
> > > > memory
> > > >
> > > > this also fixes a possible memory leak if phy_ethtool_get_stats
> > > > returns error, memory should be freed before exit
> > > >
> > > > Signed-off-by: Li RongQing <lirongqing@...du.com>
> > > > Reviewed-by: Wang Li <wangli39@...du.com>
> > > > ---
> > > >  net/core/ethtool.c | 37 ++++++++++++++++++++++++++-----------
> > > >  1 file changed, 26 insertions(+), 11 deletions(-)
> > > >
> > > > diff --git a/net/core/ethtool.c b/net/core/ethtool.c index
> > > > b1eb32419732..3e971a36e37c 100644
> > > > --- a/net/core/ethtool.c
> > > > +++ b/net/core/ethtool.c
> > > ...
> > > > @@ -1897,9 +1902,14 @@ static int ethtool_get_stats(struct
> > > > net_device
> > > *dev, void __user *useraddr)
> > > >  		return -EFAULT;
> > > >
> > > >  	stats.n_stats = n_stats;
> > > > -	data = vzalloc(array_size(n_stats, sizeof(u64)));
> > > > -	if (n_stats && !data)
> > > > -		return -ENOMEM;
> > > > +
> > > > +	if (n_stats) {
> > > > +		data = vzalloc(array_size(n_stats, sizeof(u64)));
> > > > +		if (!data)
> > > > +			return -ENOMEM;
> > > > +	} else {
> > > > +		data = NULL;
> > > > +	}
> > > >
> > > >  	ops->get_ethtool_stats(dev, &stats, data);
> > > >
> > >
> > > You avoid the vzalloc() call here but you still pass null data
> > > pointer to device's
> > > get_ethtool_stats() handler which seems to contradict what the
> > > commit message says. Is it really what you want? (The same applies
> > > to
> > > ethtool_get_phy_stats() below.)
> > >
> >
> >
> > I keep it deliberately
> >
> > ops->get_ethtool_stats(dev, &stats, data) have three parameter,
> > if n_stats is 0 [we assume the returning 0 of ops->get_sset_count is
> > correct, or get_sset_count should be fixed], data is NULL,
> > get_ethtool_stats () maybe still store the data into its seconds
> > parameter, stats, even if I did not find which drivers is like that
> 
> stats is a local variable declared as
> 
> 	struct ethtool_stats stats;
> 
> where struct ethtool_stats which looks like
> 
> struct ethtool_stats {
> 	__u32	cmd;
> 	__u32	n_stats;
> 	__u64	data[0];
> };
> 
> so that storing anything to stats.data would result in stack corruption.
> This is why ethtool_ops::get_ethtool_stats() has the third parameter telling it
> where to put the statistics.
> 
> There isn't much point touching cmd and n_stats should be set to the same
> value as we got from ethtool_ops::get_sset_counts earlier, i.e.
> zero in our case.
> 

Ok, I will send v2 which does not call ops->get_ethtool_stats, if n_stats is 0

Thanks

-RongQing

> Michal