Re: [PATCH nf 0/2] nft_set_pipapo: Fix crash due to dangling entries in mapping table

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 26 Feb 2020 11:58:04 +0100
Pablo Neira Ayuso <pablo@netfilter.org> wrote:

> On Tue, Feb 25, 2020 at 09:58:47PM +0100, Pablo Neira Ayuso wrote:
> > On Tue, Feb 25, 2020 at 09:38:15PM +0100, Stefano Brivio wrote:  
> > > On Tue, 25 Feb 2020 21:21:43 +0100
> > > Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > >   
> > > > Hi Stefano,
> > > > 
> > > > On Tue, Feb 25, 2020 at 03:34:35PM +0100, Stefano Brivio wrote:
> > > > [...]  
> > > > > This is the problem Phil reported:    
> > > > [...]  
> > > > > Or also simply with:
> > > > > 
> > > > > # nft add element t s '{ 20-30 . 40 }'
> > > > > # nft add element t s '{ 25-35 . 40 }'
> > > > > 
> > > > > the second element is silently ignored. I'm returning -EEXIST from
> > > > > nft_pipapo_insert(), but nft_add_set_elem() clears it because NLM_F_EXCL
> > > > > is not set.
> > > > > 
> > > > > Are you suggesting that this is consistent and therefore not a problem?    
> > > > 
> > > >                         NLM_F_EXCL      !NLM_F_EXCL
> > > >         exact match       EEXIST             0 [*]
> > > >         partial match     EEXIST           EEXIST
> > > > 
> > > > The [*] case would allow for element timeout/expiration updates from
> > > > the control plane for exact matches.  
> > > 
> > > A-ha. I didn't even consider that.
> > >   
> > > > Note that element updates are not
> > > > supported yet, so this check for !NLM_F_EXCL is a stub. I don't think
> > > > we should allow for updates on partial matches
> > > > 
> > > > I think what it is missing is a error to report "partial match" from
> > > > pipapo. Then, the core translates this "partial match" error to EEXIST
> > > > whether NLM_F_EXCL is set or not.  
> > > 
> > > Yes, given what you explained, I also think it's the case.
> > >   
> > > > Would this work for you?  
> > > 
> > > It would. I need to write a few more lines in nft_pipapo_insert(),
> > > because right now I don't have a special case for "entirely
> > > overlapping". Something on the lines of:
> > > 
> > > 	dup = pipapo_get(net, set, start, genmask);
> > > 	if (PTR_ERR(dup) == -ENOENT) {
> > >   
> > > -->		compare start and end key for this entry with  
> > > 		start and end key from 'ext'
> > > 
> > > Let me know if you want me to post a patch with a placeholder for
> > > whatever you have in mind, or if I can help implementing this, etc.  
> > 
> > Please, go ahead with the placeholder, it might be faster. I'll jump
> > on it.  
> 
> Sorry, I just realized I can be probably quicker on the core side.
> Here is my proposal.
> 
> I'm attaching a patch for the core. This is handling -ENOTEMPTY which
> is (ab)used to report the partial element matching.
> 
> if NLM_F_EXCL is set off, then -EEXIST becomes 0.
>                           then -ENOTEMPTY becomes -EEXIST.
> 
> Would this work for you?

Oops, I sent you my patch 80 seconds later it seems. Yes, we just need
to s/TTY/TEMPTY/ :)

Let me know how to proceed, if you want me to post that or you want to
post that (as a series?).

-- 
Stefano