On Thu, Nov 16, 2017 at 02:54:02PM +0100, Phil Sutter wrote:
> On Thu, Nov 16, 2017 at 02:38:24PM +0100, Pablo Neira Ayuso wrote:
> > On Thu, Nov 16, 2017 at 09:06:29AM +0100, Phil Sutter wrote:
> > > This introduces a rather nasty macro to call nftnl_*_fprintf() only if
> > > output_fp is valid. On the other hand, it allows to pull the common
> > > parts (format argument, event conversion) into a single place.
> > >
> > > Signed-off-by: Phil Sutter <phil@xxxxxx>
> > > ---
> > > src/netlink.c | 38 ++++++++++++++++++--------------------
> > > 1 file changed, 18 insertions(+), 20 deletions(-)
> > >
> > > diff --git a/src/netlink.c b/src/netlink.c
> > > index 845eeeffd7387..81b92ac1e2d7c 100644
> > > --- a/src/netlink.c
> > > +++ b/src/netlink.c
> > > @@ -40,6 +40,12 @@
> > > #include <iface.h>
> > >
> > > #define nft_mon_print(monh, ...) nft_print(monh->ctx->octx, __VA_ARGS__)
> > > +#define nftnl_mon_print(monh, type, obj, event) \
> > > + if (monh->ctx->octx->output_fp) { \
> > > + nftnl_##type##_fprintf(monh->ctx->octx->output_fp, \
> > > + obj, monh->format, \
> > > + netlink_msg2nftnl_of(event)); \
> > > + }
> >
> > Wait.
> >
> > Can't we just change nftnl_*_fprintf to do nothing if output_fp is
> > NULL.
> >
> > That should be safe.
>
> Looks like you just caught me trying to avoid changing libnftnl. :D
>
> Yet I still consider the macro valuable since it avoids the nasty
> pointer deref chain.
>
> I'll prepare a patch to libnftnl and then provide v2 of this patch with
> simplified nftnl_mon_print() macro. ACK?
I wonder if we can just avoid such change by making sure that
monh->ctx->octx->output_fp is always set.
May that work too?
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