[nft PATCH] parser_bison: Allow parens on RHS of relational_expr

[nft PATCH] parser_bison: Allow parens on RHS of relational_expr

[Phil Sutter]

This is useful to allow a construct such as:

| tcp flags & (syn|fin) == (syn|fin)

Before, only the parentheses on the left side were allowed, but via a
quite funny path through the parser:

* expr might be a concat_expr
* concat_expr might be a basic_expr
* basic_expr is an inclusive_or_expr
* inclusive_or_expr might be an exclusive_or_expr
* exclusive_or_expr might be an and_expr
* and_expr might be 'and_expr AMPERSAND shift_expr'
  -> here we eliminate 'flags &' in above statement
* shift_expr might be a primary_expr
* primary_expr might be '( basic_expr )'

Commit a3e60492a684b ("parser: restrict relational rhs expression
recursion") introduced rhs_expr to disallow recursion on RHS, so just
reverting that change for relational_expr is a no go. Allowing rhs_expr
to be '( rhs_expr )' though seems way too intrusive to me since it's
being used in all kinds of places, so this patch is the safest way to
allow the above I could come up with.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 src/parser_bison.y | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/parser_bison.y b/src/parser_bison.y
index 91955c187f3f0..73a0eda9a5d87 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -2254,6 +2254,10 @@ relational_expr		:	expr	/* implicit */	rhs_expr
 			{
 				$$ = relational_expr_alloc(&@2, $2, $1, $3);
 			}
+			|	expr	relational_op	'(' rhs_expr ')'
+			{
+				$$ = relational_expr_alloc(&@2, $2, $1, $4);
+			}
 			;
 
 list_rhs_expr		:	basic_rhs_expr		COMMA		basic_rhs_expr
-- 
2.10.0

Re: [nft PATCH] parser_bison: Allow parens on RHS of relational_expr

[Pablo Neira Ayuso]

On Mon, Nov 28, 2016 at 06:51:43PM +0100, Phil Sutter wrote:
> This is useful to allow a construct such as:
> 
> | tcp flags & (syn|fin) == (syn|fin)
> 
> Before, only the parentheses on the left side were allowed, but via a
> quite funny path through the parser:
> 
> * expr might be a concat_expr
> * concat_expr might be a basic_expr
> * basic_expr is an inclusive_or_expr
> * inclusive_or_expr might be an exclusive_or_expr
> * exclusive_or_expr might be an and_expr
> * and_expr might be 'and_expr AMPERSAND shift_expr'
>   -> here we eliminate 'flags &' in above statement
> * shift_expr might be a primary_expr
> * primary_expr might be '( basic_expr )'
> 
> Commit a3e60492a684b ("parser: restrict relational rhs expression
> recursion") introduced rhs_expr to disallow recursion on RHS, so just
> reverting that change for relational_expr is a no go. Allowing rhs_expr
> to be '( rhs_expr )' though seems way too intrusive to me since it's
> being used in all kinds of places, so this patch is the safest way to
> allow the above I could come up with.

Applied, thanks Phil!