netdev - Re: [PATCH net-next v4 05/12] net: rtnetlink: add bulk delete support flag

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Date:   Wed, 13 Apr 2022 18:42:24 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Nikolay Aleksandrov <razor@...ckwall.org>,
        Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, roopa@...dia.com, kuba@...nel.org,
        davem@...emloft.net, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v4 05/12] net: rtnetlink: add bulk delete support
 flag

On 4/13/22 6:21 AM, Nikolay Aleksandrov wrote:
>> If a buggy user space application is sending messages with NLM_F_BULK
>> set (unintentionally), will it break on newer kernel? I couldn't find
>> where the kernel was validating that reserved flags are not used (I
>> suspect it doesn't).
> 
> Correct, it doesn't.
> 
>>
>> Assuming the above is correct and of interest, maybe just emit a warning
>> via extack and drop the goto? Alternatively, we can see if anyone
>> complains which might never happen
>>
> 
> TBH I prefer to error out on an unsupported flag, but I get the problem. These
> weren't validated before and we start checking now. The problem is that we'll
> return an extack without an error, but the delete might also remove something.
> Hrm.. perhaps we can rephrase the error in that case (since it becomes a warning
> in iproute2 terms):
>  "NLM_F_BULK flag is set but bulk delete operation is not supported"
> So it will warn the user it has an unsupported flag.
> 
> WDYT ?
> 
> IMO we should bite the bullet and keep the error though. :)
> 

I agree. The check across the board for BULK flag on any DELETE requests
should tell us pretty quick if someone is setting that flag when it
should not be.