nftables: parser conflict between tokens & symbols

[Balazs Scheidler <balazs.scheidler@balabit.com>]

Hi,

I've noticed that our set of keywords in nftables is pretty rich and
this can cause conflicts in the grammar when a keyword is also used
as a symbol.

For instance, we do have a "redirect" expression and "redirect" as
a word is also used as an ICMP message type.

# here is the redirect expression in action, which works:
$ nft add rule tcp dport 80 redirect to 8080

# here's an ICMP rule that works
$ nft add rule filter input icmp type echo-request accept

# here's an ICMP rule that should work, but it doesn't
$ nft add rule filter input icmp type redirect accept

The root cause is that "redirect" is now recognized as a token, whereas the
icmp type is expecting a STRING token.

I have tried to solve this but the idea I had didn't work out, and I don't
really have more time now to fix it, but still thought this information
would be useful.

Cheers,
Bazsi