netdev - Re: [PATCH net] net: rtnetlink: fix bugs in rtnl_alt

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Date:   Wed, 12 Feb 2020 22:58:01 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>, Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, Jiri Pirko <jiri@...lanox.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] net: rtnetlink: fix bugs in rtnl_alt_ifname()



On 2/12/20 10:45 PM, Jiri Pirko wrote:
> Thu, Feb 13, 2020 at 05:58:26AM CET, edumazet@...gle.com wrote:
>> Since IFLA_ALT_IFNAME is an NLA_STRING, we have no
>> guarantee it is nul terminated.
>>
>> We should use nla_strdup() instead of kstrdup(), since this
>> helper will make sure not accessing out-of-bounds data.
>>
>> 
>> Fixes: 36fbf1e52bd3 ("net: rtnetlink: add linkprop commands to add and delete alternative ifnames")
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> Cc: Jiri Pirko <jiri@...lanox.com>
>> Reported-by: syzbot <syzkaller@...glegroups.com>
>> ---
>> net/core/rtnetlink.c | 26 ++++++++++++--------------
>> 1 file changed, 12 insertions(+), 14 deletions(-)
>>
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index 09c44bf2e1d28842d77b4ed442ef2c051a25ad21..e1152f4ffe33efb0a69f17a1f5940baa04942e5b 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
>> @@ -3504,27 +3504,25 @@ static int rtnl_alt_ifname(int cmd, struct net_device *dev, struct nlattr *attr,
>> 	if (err)
>> 		return err;
>>
>> -	alt_ifname = nla_data(attr);
>> +	alt_ifname = nla_strdup(attr, GFP_KERNEL);
>> +	if (!alt_ifname)
>> +		return -ENOMEM;
>> +
>> 	if (cmd == RTM_NEWLINKPROP) {
>> -		alt_ifname = kstrdup(alt_ifname, GFP_KERNEL);
>> -		if (!alt_ifname)
>> -			return -ENOMEM;
>> 		err = netdev_name_node_alt_create(dev, alt_ifname);
>> -		if (err) {
>> -			kfree(alt_ifname);
>> -			return err;
>> -		}
>> +		if (!err)
>> +			alt_ifname = NULL;
>> 	} else if (cmd == RTM_DELLINKPROP) {
>> 		err = netdev_name_node_alt_destroy(dev, alt_ifname);
>> -		if (err)
>> -			return err;
>> 	} else {
> 
> 
>> -		WARN_ON(1);
>> -		return 0;
>> +		WARN_ON_ONCE(1);
>> +		err = -EINVAL;
> 
> These 4 lines do not seem to be related to the rest of the patch. Should
> it be a separate patch?

Well, we have to kfree(alt_ifname).

Generally speaking I tried to avoid return in the middle of this function.

The WARN_ON(1) is dead code today, making it a WARN_ON_ONCE(1) is simply
a matter of avoiding syslog floods if this path is ever triggered in the future.

> 
> Otherwise, the patch looks fine to me.
>

Thanks !