Re: [nft PATCH] misspell: Avoid segfault with anonymous chains

[Phil Sutter <phil@nwl.cc>]

On Fri, Mar 04, 2022 at 12:11:53PM +0100, Pablo Neira Ayuso wrote:
> Hi Phil,
> 
> On Fri, Mar 04, 2022 at 11:37:11AM +0100, Phil Sutter wrote:
> > When trying to add a rule which contains an anonymous chain to a
> > non-existent chain, string_misspell_update() is called with a NULL
> > string because the anonymous chain has no name. Avoid this by making the
> > function NULL-pointer tolerant.
> > 
> > c330152b7f777 ("src: support for implicit chain bindings")
> > 
> > Signed-off-by: Phil Sutter <phil@nwl.cc>
> > ---
> >  src/misspell.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/misspell.c b/src/misspell.c
> > index 6536d7557a445..f213a240005e6 100644
> > --- a/src/misspell.c
> > +++ b/src/misspell.c
> > @@ -80,8 +80,8 @@ int string_misspell_update(const char *a, const char *b,
> >  {
> >  	unsigned int len_a, len_b, max_len, min_len, distance, threshold;
> >  
> > -	len_a = strlen(a);
> > -	len_b = strlen(b);
> > +	len_a = a ? strlen(a) : 0;
> > +	len_b = b ? strlen(b) : 0;
> 
> string_distance() assumes non-NULL too.

Which is called from string_misspell_update() only which with my patch
returns early due to 'max_len <= 1'.

> probably shortcircuit chain_lookup_fuzzy() earlier since h->chain.name
> is always NULL, to avoid the useless loop.

Fine with me, too! What about allocating a name for the anonymous chain
instead? I guess similar treatment as with sets would make sense. Might
also help with netlink debug output:

| # nft --debug=netlink insert rule inet x y 'goto { accept; }'
| inet (null) (null) use 0
| inet x
|   [ immediate reg 0 accept ]
| 
|   inet x y
|     [ immediate reg 0 goto ]
| [...]

Thanks, Phil