Re: [PATCH v2] bpf: Add length check for SK_DIAG_BPF_STORAGE_REQ_MAP_FD parsing

[Leon Romanovsky <leon@kernel.org>]

On Tue, Jul 25, 2023 at 01:24:38PM +0800, Lin Ma wrote:
> Hello Leon,
> 
> > 
> > Jakub, it seems like Lin adds this check to all nla_for_each_nested() loops.
> > IMHO, the better change will be to change nla_for_each_nested() skip empty/not valid NLAs.
> > 
> > Thanks
> 
> I guess you just get these fixes misunderstood. I do not add the nla_len check
> to  **all nla_for_each_nested** :(. I only add checks to those who do not access 
> the attributes without verifying the length, which is buggy.
> 
> The others, either do a similar nla_len check already or just do nla_validate
> somewhere else. That is to say, they **validate** the relevant attributes.
> 
> In short, nla_for_each_nested is just a loop macro that iterates the nlattrs,
> like nla_for_each macro. It is weird for them to do nlattr validation as there
> could have already been a call to nla_validate to ensure those attributes are
> correct. That is, for those who do not, a simple nla_len check is the simplest
> and most efficient choice.

My concern is related to maintainability in long run. Your check adds
another layer of cabal knowledge which will be copied/pasted in other
places.

Thanks

> 
> Regards
> Lin