Hi Pablo,
On Sun, Jan 12, 2020 at 11:40:27AM +0100, Pablo Neira Ayuso wrote:
> On Sun, Jan 12, 2020 at 11:28:02AM +0100, Pablo Neira Ayuso wrote:
> > On Fri, Jan 10, 2020 at 01:53:11PM +0100, Phil Sutter wrote:
> > > On Thu, Jan 09, 2020 at 06:21:13PM +0100, Pablo Neira Ayuso wrote:
> > > [...]
> > > > diff --git a/include/nftables/libnftables.h b/include/nftables/libnftables.h
> > > > index 765b20dd71ee..887628959ac6 100644
> > > > --- a/include/nftables/libnftables.h
> > > > +++ b/include/nftables/libnftables.h
> > > > @@ -34,10 +34,13 @@ enum nft_debug_level {
> > > > * Possible flags to pass to nft_ctx_new()
> > > > */
> > > > #define NFT_CTX_DEFAULT 0
> > > > +#define NFT_CTX_NETNS 1
> > >
> > > What is this needed for?
> >
> > The socket is initialized from nft_ctx_init(), and such initialization
> > needs to happen after the netns switch.
>
> s/nft_ctx_init()/nft_ctx_new()
Ah, I missed that socket init in nft_ctx_new() happens only if flags is
zero.
> > > > struct nft_ctx *nft_ctx_new(uint32_t flags);
> > > > void nft_ctx_free(struct nft_ctx *ctx);
> > > >
> > > > +int nft_ctx_set_netns(struct nft_ctx *ctx, const char *netns);
> > >
> > > Is there a way to select init ns again?
> >
> > AFAIK, setns() does not let you go back to init ns once set.
I noticed something I find worse, namely that libnftables as a library
changes the application's netns. Anything it does after changing the
context's netns applies to that netns only, no matter if it's creating a
new nft context with NFT_CtX_DEFAULT flag or call iproute via system().
If we can't find a way to exit the netns again, one can safely assume
that we are trapping a user's application in a netns with this feature.
Maybe we should restrict per-netns operation to nft utility and perform
the netns switch there? Maybe we could provide a "switch_netns()"
routine in libnftables which is not bound to nft context so users may
use it in their application?
Cheers, Phil
