From 80f3c19bc1b989ab7ba2b917193e8bd3f998ba39 Mon Sep 17 00:00:00 2001
From: Florian Westphal <fw@strlen.de>
Date: Mon, 8 Mar 2021 18:18:33 +0100
Subject: [PATCH] scanner: introduce start condition stack

Add a small initial chunk of flex start conditionals.

This starts with two low-hanging fruits, numgen and j/symhash.

NUMGEN and HASH start conditions are entered from flex when
the corresponding expression token is encountered.

Flex returns to the INIT condition when the bison parser
has seen a complete numgen/hash statement.

This intentionally uses a stack rather than BEGIN()
to eventually support nested states.

The scanner_pop_start_cond() function argument is not used yet, but
will need to be used later to deal with nesting.

Signed-off-by: Florian Westphal <fw@strlen.de>
(cherry picked from commit 5896772fe3c5f01696188ea04957a825ee601b12)
---
 include/parser.h   |  8 ++++++++
 src/parser_bison.y | 11 +++++++----
 src/scanner.l      | 36 +++++++++++++++++++++++++++++-------
 3 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/include/parser.h b/include/parser.h
index 9baa3a4db789f..b2ebd7aa226c5 100644
--- a/include/parser.h
+++ b/include/parser.h
@@ -26,6 +26,12 @@ struct parser_state {
 	struct list_head		*cmds;
 };
 
+enum startcond_type {
+	PARSER_SC_BEGIN,
+	PARSER_SC_EXPR_HASH,
+	PARSER_SC_EXPR_NUMGEN,
+};
+
 struct mnl_socket;
 
 extern void parser_init(struct nft_ctx *nft, struct parser_state *state,
@@ -45,4 +51,6 @@ extern void scanner_push_buffer(void *scanner,
 				const struct input_descriptor *indesc,
 				const char *buffer);
 
+extern void scanner_pop_start_cond(void *scanner, enum startcond_type sc);
+
 #endif /* NFTABLES_PARSER_H */
diff --git a/src/parser_bison.y b/src/parser_bison.y
index 8644f66106496..da3fafcd1eeb1 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -857,6 +857,9 @@ opt_newline		:	NEWLINE
 		 	|	/* empty */
 			;
 
+close_scope_hash	: { scanner_pop_start_cond(nft->scanner, PARSER_SC_EXPR_HASH); };
+close_scope_numgen	: { scanner_pop_start_cond(nft->scanner, PARSER_SC_EXPR_NUMGEN); };
+
 common_block		:	INCLUDE		QUOTED_STRING	stmt_separator
 			{
 				if (scanner_include_file(nft, scanner, $2, &@$) < 0) {
@@ -4811,7 +4814,7 @@ numgen_type		:	INC		{ $$ = NFT_NG_INCREMENTAL; }
 			|	RANDOM		{ $$ = NFT_NG_RANDOM; }
 			;
 
-numgen_expr		:	NUMGEN	numgen_type	MOD	NUM	offset_opt
+numgen_expr		:	NUMGEN	numgen_type	MOD	NUM	offset_opt	close_scope_numgen
 			{
 				$$ = numgen_expr_alloc(&@$, $2, $4, $5);
 			}
@@ -4868,17 +4871,17 @@ xfrm_expr		:	IPSEC	xfrm_dir	xfrm_spnum	xfrm_state_key
 			}
 			;
 
-hash_expr		:	JHASH		expr	MOD	NUM	SEED	NUM	offset_opt
+hash_expr		:	JHASH		expr	MOD	NUM	SEED	NUM	offset_opt	close_scope_hash
 			{
 				$$ = hash_expr_alloc(&@$, $4, true, $6, $7, NFT_HASH_JENKINS);
 				$$->hash.expr = $2;
 			}
-			|	JHASH		expr	MOD	NUM	offset_opt
+			|	JHASH		expr	MOD	NUM	offset_opt	close_scope_hash
 			{
 				$$ = hash_expr_alloc(&@$, $4, false, 0, $5, NFT_HASH_JENKINS);
 				$$->hash.expr = $2;
 			}
-			|	SYMHASH		MOD	NUM	offset_opt
+			|	SYMHASH		MOD	NUM	offset_opt	close_scope_hash
 			{
 				$$ = hash_expr_alloc(&@$, $3, false, 0, $4, NFT_HASH_SYM);
 			}
diff --git a/src/scanner.l b/src/scanner.l
index 8bde1fbe912d8..ec8f252fbc8c8 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -98,6 +98,8 @@ static void reset_pos(struct parser_state *state, struct location *loc)
 	state->indesc->column		= 1;
 }
 
+static void scanner_push_start_cond(void *scanner, enum startcond_type type);
+
 #define YY_USER_ACTION {					\
 	update_pos(yyget_extra(yyscanner), yylloc, yyleng);	\
 	update_offset(yyget_extra(yyscanner), yylloc, yyleng);	\
@@ -193,6 +195,9 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 %option yylineno
 %option nodefault
 %option warn
+%option stack
+%s SCANSTATE_EXPR_HASH
+%s SCANSTATE_EXPR_NUMGEN
 
 %%
 
@@ -551,15 +556,21 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 "state"			{ return STATE; }
 "status"		{ return STATUS; }
 
-"numgen"		{ return NUMGEN; }
-"inc"			{ return INC; }
-"mod"			{ return MOD; }
-"offset"		{ return OFFSET; }
+"numgen"		{ scanner_push_start_cond(yyscanner, SCANSTATE_EXPR_NUMGEN); return NUMGEN; }
+<SCANSTATE_EXPR_NUMGEN>{
+	"inc"		{ return INC; }
+}
 
-"jhash"			{ return JHASH; }
-"symhash"		{ return SYMHASH; }
-"seed"			{ return SEED; }
+"jhash"			{ scanner_push_start_cond(yyscanner, SCANSTATE_EXPR_HASH); return JHASH; }
+"symhash"		{ scanner_push_start_cond(yyscanner, SCANSTATE_EXPR_HASH); return SYMHASH; }
 
+<SCANSTATE_EXPR_HASH>{
+	"seed"		{ return SEED; }
+}
+<SCANSTATE_EXPR_HASH,SCANSTATE_EXPR_NUMGEN>{
+	"mod"		{ return MOD; }
+	"offset"	{ return OFFSET; }
+}
 "dup"			{ return DUP; }
 "fwd"			{ return FWD; }
 
@@ -973,3 +984,14 @@ void scanner_destroy(struct nft_ctx *nft)
 	input_descriptor_list_destroy(state);
 	yylex_destroy(nft->scanner);
 }
+
+static void scanner_push_start_cond(void *scanner, enum startcond_type type)
+{
+	yy_push_state((int)type, scanner);
+}
+
+void scanner_pop_start_cond(void *scanner, enum startcond_type t)
+{
+	yy_pop_state(scanner);
+	(void)yy_top_state(scanner); /* suppress gcc warning wrt. unused function */
+}
-- 
2.33.0