[PATCH iptables v2]: Support the iptables lock in ip[6]tables-restore

[PATCH iptables v2]: Support the iptables lock in ip[6]tables-restore

[Lorenzo Colitti]

This series adds support for -w and -W to ip[6]tables-restore,
which currently do not perform any locking.

The lock is not acquired on startup. Instead, it is acquired when
a new table handle is created (on encountering '*') and released
when the table is committed (COMMIT). This makes it possible to
keep long-running iptables-restore processes in the background
(for example, reading commands from a pipe opened by a system
management daemon) and simultaneously run iptables commands.
An example usage is Android's IptablesRestoreController.cpp.

The first patch factors out to common functions the code that
parses -w and -W, in order not to have to add more copies of it.
The second patch actually adds support to iptables-restore.

[PATCH iptables v2 1/2] iptables: remove duplicated argument parsing code

[Lorenzo Colitti]

1. Factor out repeated code to a new xs_has_arg function.
2. Add a new parse_wait_time option to parse the value of -w.
3. Make parse_wait_interval take argc and argv so its callers
   can be simpler.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
---
 iptables/ip6tables.c   | 62 +++++++++++++-------------------------------------
 iptables/iptables.c    | 62 +++++++++++++-------------------------------------
 iptables/xshared.c     | 35 ++++++++++++++++++++++++++--
 iptables/xshared.h     |  4 +++-
 iptables/xtables-arp.c | 30 ++++++++----------------
 iptables/xtables.c     | 62 ++++++++++++++------------------------------------
 6 files changed, 95 insertions(+), 160 deletions(-)

diff --git a/iptables/ip6tables.c b/iptables/ip6tables.c
index 0bd415dec5..4d77721b04 100644
--- a/iptables/ip6tables.c
+++ b/iptables/ip6tables.c
@@ -1400,8 +1400,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_DELETE, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				rulenum = parse_rulenumber(argv[optind++]);
 				command = CMD_DELETE_NUM;
 			}
@@ -1411,8 +1410,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_REPLACE, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1424,8 +1422,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_INSERT, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			else rulenum = 1;
 			break;
@@ -1434,11 +1431,9 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_LIST,
 				    CMD_ZERO | CMD_ZERO_NUM, cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			break;
 
@@ -1446,11 +1441,9 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_LIST_RULES,
 				    CMD_ZERO | CMD_ZERO_NUM, cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			break;
 
@@ -1458,8 +1451,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_FLUSH, CMD_NONE,
 				    cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1467,11 +1459,9 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_ZERO, CMD_LIST|CMD_LIST_RULES,
 				    cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				rulenum = parse_rulenumber(argv[optind++]);
 				command = CMD_ZERO_NUM;
 			}
@@ -1488,8 +1478,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_DELETE_CHAIN, CMD_NONE,
 				    cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1497,8 +1486,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_RENAME_CHAIN, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				newname = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1511,8 +1499,7 @@ int do_command6(int argc, char *argv[], char **table,
 			add_command(&command, CMD_SET_POLICY, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				policy = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1622,16 +1609,7 @@ int do_command6(int argc, char *argv[], char **table,
 					      "You cannot use `-w' from "
 					      "ip6tables-restore");
 			}
-			wait = -1;
-			if (optarg) {
-				if (sscanf(optarg, "%i", &wait) != 1)
-					xtables_error(PARAMETER_PROBLEM,
-						"wait seconds not numeric");
-			} else if (optind < argc && argv[optind][0] != '-'
-						 && argv[optind][0] != '!')
-				if (sscanf(argv[optind++], "%i", &wait) != 1)
-					xtables_error(PARAMETER_PROBLEM,
-						"wait seconds not numeric");
+			wait = parse_wait_time(argc, argv);
 			break;
 
 		case 'W':
@@ -1640,14 +1618,7 @@ int do_command6(int argc, char *argv[], char **table,
 					      "You cannot use `-W' from "
 					      "ip6tables-restore");
 			}
-			if (optarg)
-				parse_wait_interval(optarg, &wait_interval);
-			else if (optind < argc &&
-				argv[optind][0] != '-' &&
-				argv[optind][0] != '!')
-				parse_wait_interval(argv[optind++],
-						    &wait_interval);
-
+			parse_wait_interval(argc, argv, &wait_interval);
 			wait_interval_set = true;
 			break;
 
@@ -1697,8 +1668,7 @@ int do_command6(int argc, char *argv[], char **table,
 			bcnt = strchr(pcnt + 1, ',');
 			if (bcnt)
 			    bcnt++;
-			if (!bcnt && optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (!bcnt && xs_has_arg(argc, argv))
 				bcnt = argv[optind++];
 			if (!bcnt)
 				xtables_error(PARAMETER_PROBLEM,
diff --git a/iptables/iptables.c b/iptables/iptables.c
index e0d092f0b6..04be5abb10 100644
--- a/iptables/iptables.c
+++ b/iptables/iptables.c
@@ -1393,8 +1393,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_DELETE, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				rulenum = parse_rulenumber(argv[optind++]);
 				command = CMD_DELETE_NUM;
 			}
@@ -1404,8 +1403,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_REPLACE, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1417,8 +1415,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_INSERT, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			else rulenum = 1;
 			break;
@@ -1427,11 +1424,9 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_LIST,
 				    CMD_ZERO | CMD_ZERO_NUM, cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			break;
 
@@ -1439,11 +1434,9 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_LIST_RULES,
 				    CMD_ZERO|CMD_ZERO_NUM, cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			break;
 
@@ -1451,8 +1444,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_FLUSH, CMD_NONE,
 				    cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1460,11 +1452,9 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_ZERO, CMD_LIST|CMD_LIST_RULES,
 				    cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				rulenum = parse_rulenumber(argv[optind++]);
 				command = CMD_ZERO_NUM;
 			}
@@ -1481,8 +1471,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_DELETE_CHAIN, CMD_NONE,
 				    cs.invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1490,8 +1479,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_RENAME_CHAIN, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				newname = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1504,8 +1492,7 @@ int do_command4(int argc, char *argv[], char **table,
 			add_command(&command, CMD_SET_POLICY, CMD_NONE,
 				    cs.invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				policy = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1613,16 +1600,7 @@ int do_command4(int argc, char *argv[], char **table,
 					      "You cannot use `-w' from "
 					      "iptables-restore");
 			}
-			wait = -1;
-			if (optarg) {
-				if (sscanf(optarg, "%i", &wait) != 1)
-					xtables_error(PARAMETER_PROBLEM,
-						"wait seconds not numeric");
-			} else if (optind < argc && argv[optind][0] != '-'
-						 && argv[optind][0] != '!')
-				if (sscanf(argv[optind++], "%i", &wait) != 1)
-					xtables_error(PARAMETER_PROBLEM,
-						"wait seconds not numeric");
+			wait = parse_wait_time(argc, argv);
 			break;
 
 		case 'W':
@@ -1631,14 +1609,7 @@ int do_command4(int argc, char *argv[], char **table,
 					      "You cannot use `-W' from "
 					      "iptables-restore");
 			}
-			if (optarg)
-				parse_wait_interval(optarg, &wait_interval);
-			else if (optind < argc &&
-				 argv[optind][0] != '-' &&
-				 argv[optind][0] != '!')
-				parse_wait_interval(argv[optind++],
-						    &wait_interval);
-
+			parse_wait_interval(argc, argv, &wait_interval);
 			wait_interval_set = true;
 			break;
 
@@ -1688,8 +1659,7 @@ int do_command4(int argc, char *argv[], char **table,
 			bcnt = strchr(pcnt + 1, ',');
 			if (bcnt)
 			    bcnt++;
-			if (!bcnt && optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (!bcnt && xs_has_arg(argc, argv))
 				bcnt = argv[optind++];
 			if (!bcnt)
 				xtables_error(PARAMETER_PROBLEM,
diff --git a/iptables/xshared.c b/iptables/xshared.c
index 383ecf2cf2..dd5f8be028 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -284,12 +284,36 @@ bool xtables_lock(int wait, struct timeval *wait_interval)
 	}
 }
 
-void parse_wait_interval(const char *str, struct timeval *wait_interval)
+int parse_wait_time(int argc, char *argv[])
 {
+	int wait = -1;
+
+	if (optarg) {
+		if (sscanf(optarg, "%i", &wait) != 1)
+			xtables_error(PARAMETER_PROBLEM,
+				"wait seconds not numeric");
+	} else if (xs_has_arg(argc, argv))
+		if (sscanf(argv[optind++], "%i", &wait) != 1)
+			xtables_error(PARAMETER_PROBLEM,
+				"wait seconds not numeric");
+
+	return wait;
+}
+
+void parse_wait_interval(int argc, char *argv[], struct timeval *wait_interval)
+{
+	const char *arg;
 	unsigned int usec;
 	int ret;
 
-	ret = sscanf(str, "%u", &usec);
+	if (optarg)
+		arg = optarg;
+	else if (xs_has_arg(argc, argv))
+		arg = argv[optind++];
+	else
+		return;
+
+	ret = sscanf(arg, "%u", &usec);
 	if (ret == 1) {
 		if (usec > 999999)
 			xtables_error(PARAMETER_PROBLEM,
@@ -302,3 +326,10 @@ void parse_wait_interval(const char *str, struct timeval *wait_interval)
 	}
 	xtables_error(PARAMETER_PROBLEM, "wait interval not numeric");
 }
+
+inline bool xs_has_arg(int argc, char *argv[])
+{
+	return optind < argc &&
+	       argv[optind][0] != '-' &&
+	       argv[optind][0] != '!';
+}
diff --git a/iptables/xshared.h b/iptables/xshared.h
index 18b1cf3764..d8a697ae66 100644
--- a/iptables/xshared.h
+++ b/iptables/xshared.h
@@ -88,7 +88,9 @@ extern void xs_init_target(struct xtables_target *);
 extern void xs_init_match(struct xtables_match *);
 bool xtables_lock(int wait, struct timeval *wait_interval);
 
-void parse_wait_interval(const char *str, struct timeval *wait_interval);
+int parse_wait_time(int argc, char *argv[]);
+void parse_wait_interval(int argc, char *argv[], struct timeval *wait_interval);
+bool xs_has_arg(int argc, char *argv[]);
 
 extern const struct xtables_afinfo *afinfo;
 
diff --git a/iptables/xtables-arp.c b/iptables/xtables-arp.c
index bd6d57c2d8..6aa000a14d 100644
--- a/iptables/xtables-arp.c
+++ b/iptables/xtables-arp.c
@@ -984,8 +984,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_DELETE, CMD_NONE,
 				    invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				rulenum = parse_rulenumber(argv[optind++]);
 				command = CMD_DELETE_NUM;
 			}
@@ -995,8 +994,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_REPLACE, CMD_NONE,
 				    invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1008,8 +1006,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_INSERT, CMD_NONE,
 				    invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				rulenum = parse_rulenumber(argv[optind++]);
 			else rulenum = 1;
 			break;
@@ -1018,8 +1015,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_LIST, CMD_ZERO,
 				    invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1027,8 +1023,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_FLUSH, CMD_NONE,
 				    invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1036,8 +1031,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_ZERO, CMD_LIST,
 				    invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1059,8 +1053,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_DELETE_CHAIN, CMD_NONE,
 				    invert);
 			if (optarg) chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				chain = argv[optind++];
 			break;
 
@@ -1068,8 +1061,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_RENAME_CHAIN, CMD_NONE,
 				    invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				newname = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1082,8 +1074,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			add_command(&command, CMD_SET_POLICY, CMD_NONE,
 				    invert);
 			chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				policy = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1286,8 +1277,7 @@ int do_commandarp(struct nft_handle *h, int argc, char *argv[], char **table)
 			set_option(&options, OPT_COUNTERS, &cs.fw.arp.invflags,
 				   invert);
 			pcnt = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				bcnt = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
diff --git a/iptables/xtables.c b/iptables/xtables.c
index d222ae991d..286866f75d 100644
--- a/iptables/xtables.c
+++ b/iptables/xtables.c
@@ -744,8 +744,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 			add_command(&p->command, CMD_DELETE, CMD_NONE,
 				    cs->invert);
 			p->chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				p->rulenum = parse_rulenumber(argv[optind++]);
 				p->command = CMD_DELETE_NUM;
 			}
@@ -755,8 +754,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 			add_command(&p->command, CMD_REPLACE, CMD_NONE,
 				    cs->invert);
 			p->chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				p->rulenum = parse_rulenumber(argv[optind++]);
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -768,8 +766,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 			add_command(&p->command, CMD_INSERT, CMD_NONE,
 				    cs->invert);
 			p->chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				p->rulenum = parse_rulenumber(argv[optind++]);
 			else
 				p->rulenum = 1;
@@ -780,11 +777,9 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 				    CMD_ZERO | CMD_ZERO_NUM, cs->invert);
 			if (optarg)
 				p->chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				p->chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				p->rulenum = parse_rulenumber(argv[optind++]);
 			break;
 
@@ -793,11 +788,9 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 				    CMD_ZERO|CMD_ZERO_NUM, cs->invert);
 			if (optarg)
 				p->chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				p->chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				p->rulenum = parse_rulenumber(argv[optind++]);
 			break;
 
@@ -806,8 +799,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 				    cs->invert);
 			if (optarg)
 				p->chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				p->chain = argv[optind++];
 			break;
 
@@ -816,11 +808,9 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 				    CMD_LIST|CMD_LIST_RULES, cs->invert);
 			if (optarg)
 				p->chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				p->chain = argv[optind++];
-			if (optind < argc && argv[optind][0] != '-'
-				&& argv[optind][0] != '!') {
+			if (xs_has_arg(argc, argv)) {
 				p->rulenum = parse_rulenumber(argv[optind++]);
 				p->command = CMD_ZERO_NUM;
 			}
@@ -845,8 +835,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 				    cs->invert);
 			if (optarg)
 				p->chain = optarg;
-			else if (optind < argc && argv[optind][0] != '-'
-				 && argv[optind][0] != '!')
+			else if (xs_has_arg(argc, argv))
 				p->chain = argv[optind++];
 			break;
 
@@ -854,8 +843,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 			add_command(&p->command, CMD_RENAME_CHAIN, CMD_NONE,
 				    cs->invert);
 			p->chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				p->newname = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -868,8 +856,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 			add_command(&p->command, CMD_SET_POLICY, CMD_NONE,
 				    cs->invert);
 			p->chain = optarg;
-			if (optind < argc && argv[optind][0] != '-'
-			    && argv[optind][0] != '!')
+			if (xs_has_arg(argc, argv))
 				p->policy = argv[optind++];
 			else
 				xtables_error(PARAMETER_PROBLEM,
@@ -1014,15 +1001,8 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 					      "You cannot use `-w' from "
 					      "iptables-restore");
 			}
-			if (optarg) {
-				if (sscanf(optarg, "%i", &wait) != 1)
-					xtables_error(PARAMETER_PROBLEM,
-						      "wait seconds not numeric");
-			} else if (optind < argc && argv[optind][0] != '-'
-				   && argv[optind][0] != '!')
-				if (sscanf(argv[optind++], "%i", &wait) != 1)
-					xtables_error(PARAMETER_PROBLEM,
-						      "wait seconds not numeric");
+
+			wait = parse_wait_time(argc, argv);
 			break;
 
 		case 'W':
@@ -1031,14 +1011,8 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 					      "You cannot use `-W' from "
 					      "iptables-restore");
 			}
-			if (optarg)
-				parse_wait_interval(optarg, &wait_interval);
-			else if (optind < argc &&
-				   argv[optind][0] != '-' &&
-				   argv[optind][0] != '!')
-				parse_wait_interval(argv[optind++],
-						    &wait_interval);
 
+			parse_wait_interval(argc, argv, &wait_interval);
 			wait_interval_set = true;
 			break;
 
@@ -1058,9 +1032,7 @@ void do_parse(struct nft_handle *h, int argc, char *argv[],
 			args->bcnt = strchr(args->pcnt + 1, ',');
 			if (args->bcnt)
 			    args->bcnt++;
-			if (!args->bcnt && optind < argc &&
-			    argv[optind][0] != '-' &&
-			    argv[optind][0] != '!')
+			if (!args->bcnt && xs_has_arg(argc, argv))
 				args->bcnt = argv[optind++];
 			if (!args->bcnt)
 				xtables_error(PARAMETER_PROBLEM,
-- 
2.12.0.367.g23dc2f6d3c-goog

[PATCH iptables v2 2/2] iptables-restore: support acquiring the lock.

[Lorenzo Colitti]

Currently, ip[6]tables-restore does not perform any locking, so it
is not safe to use concurrently with ip[6]tables.

This patch makes ip[6]tables-restore wait for the lock if -w
was specified. Arguments to -w and -W are supported in the same
was as they are in ip[6]tables.

The lock is not acquired on startup. Instead, it is acquired when
a new table handle is created (on encountering '*') and released
when the table is committed (COMMIT). This makes it possible to
keep long-running iptables-restore processes in the background
(for example, reading commands from a pipe opened by a system
management daemon) and simultaneously run iptables commands.

If -w is not specified, then the command proceeds without taking
the lock.

Tested as follows:

1. Run iptables-restore -w, and check that iptables commands work
   with or without -w.
2. Type "*filter" into the iptables-restore input. Verify that
   a) ip[6]tables commands without -w fail with "another app is
      currently holding the xtables lock...".
   b) ip[6]tables commands with "-w 2" fail after 2 seconds.
   c) ip[6]tables commands with "-w" hang until "COMMIT" is
      typed into the iptables-restore window.
3. With the lock held by an ip6tables-restore process:
     strace -e flock /tmp/iptables/sbin/iptables-restore -w 1 -W 100000
   shows 11 calls to flock and fails.
4. Run an iptables-restore with -w and one without -w, and check:
   a) Type "*filter" in the first and then the second, and the
      second exits with an error.
   b) Type "*filter" in the second and "*filter" "-S" "COMMIT"
      into the first. The rules are listed only when the first
      copy sees "COMMIT".

Signed-off-by: Narayan Kamath <narayan@google.com>
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
---
 iptables/ip6tables-restore.c | 55 ++++++++++++++++++++++++++++++++++----------
 iptables/ip6tables.c         |  2 +-
 iptables/iptables-restore.c  | 55 ++++++++++++++++++++++++++++++++++----------
 iptables/iptables.c          |  2 +-
 iptables/xshared.c           | 18 ++++++++++-----
 iptables/xshared.h           | 23 +++++++++++++++++-
 6 files changed, 122 insertions(+), 33 deletions(-)

diff --git a/iptables/ip6tables-restore.c b/iptables/ip6tables-restore.c
index dc0acb05a4..8a47f09c95 100644
--- a/iptables/ip6tables-restore.c
+++ b/iptables/ip6tables-restore.c
@@ -15,6 +15,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "ip6tables.h"
+#include "xshared.h"
 #include "xtables.h"
 #include "libiptc/libip6tc.h"
 #include "ip6tables-multi.h"
@@ -25,17 +26,23 @@
 #define DEBUGP(x, args...)
 #endif
 
-static int counters = 0, verbose = 0, noflush = 0;
+static int counters = 0, verbose = 0, noflush = 0, wait = 0;
+
+static struct timeval wait_interval = {
+	.tv_sec	= 1,
+};
 
 /* Keeping track of external matches and targets.  */
 static const struct option options[] = {
-	{.name = "counters", .has_arg = false, .val = 'c'},
-	{.name = "verbose",  .has_arg = false, .val = 'v'},
-	{.name = "test",     .has_arg = false, .val = 't'},
-	{.name = "help",     .has_arg = false, .val = 'h'},
-	{.name = "noflush",  .has_arg = false, .val = 'n'},
-	{.name = "modprobe", .has_arg = true,  .val = 'M'},
-	{.name = "table",    .has_arg = true,  .val = 'T'},
+	{.name = "counters",      .has_arg = 0, .val = 'c'},
+	{.name = "verbose",       .has_arg = 0, .val = 'v'},
+	{.name = "test",          .has_arg = 0, .val = 't'},
+	{.name = "help",          .has_arg = 0, .val = 'h'},
+	{.name = "noflush",       .has_arg = 0, .val = 'n'},
+	{.name = "modprobe",      .has_arg = 1, .val = 'M'},
+	{.name = "table",         .has_arg = 1, .val = 'T'},
+	{.name = "wait",          .has_arg = 2, .val = 'w'},
+	{.name = "wait-interval", .has_arg = 2, .val = 'W'},
 	{NULL},
 };
 
@@ -43,14 +50,16 @@ static void print_usage(const char *name, const char *version) __attribute__((no
 
 static void print_usage(const char *name, const char *version)
 {
-	fprintf(stderr, "Usage: %s [-c] [-v] [-t] [-h] [-n] [-T table] [-M command]\n"
+	fprintf(stderr, "Usage: %s [-c] [-v] [-t] [-h] [-n] [-w secs] [-W usecs] [-T table] [-M command]\n"
 			"	   [ --counters ]\n"
 			"	   [ --verbose ]\n"
 			"	   [ --test ]\n"
 			"	   [ --help ]\n"
 			"	   [ --noflush ]\n"
+			"	   [ --wait=<seconds>\n"
+			"	   [ --wait-interval=<usecs>\n"
 			"	   [ --table=<TABLE> ]\n"
-			"          [ --modprobe=<command> ]\n", name);
+			"	   [ --modprobe=<command> ]\n", name);
 
 	exit(1);
 }
@@ -181,7 +190,7 @@ int ip6tables_restore_main(int argc, char *argv[])
 {
 	struct xtc_handle *handle = NULL;
 	char buffer[10240];
-	int c;
+	int c, lock;
 	char curtable[XT_TABLE_MAXNAMELEN + 1];
 	FILE *in;
 	int in_table = 0, testing = 0;
@@ -189,6 +198,7 @@ int ip6tables_restore_main(int argc, char *argv[])
 	const struct xtc_ops *ops = &ip6tc_ops;
 
 	line = 0;
+	lock = XT_LOCK_NOT_ACQUIRED;
 
 	ip6tables_globals.program_name = "ip6tables-restore";
 	c = xtables_init_all(&ip6tables_globals, NFPROTO_IPV6);
@@ -203,7 +213,7 @@ int ip6tables_restore_main(int argc, char *argv[])
 	init_extensions6();
 #endif
 
-	while ((c = getopt_long(argc, argv, "bcvthnM:T:", options, NULL)) != -1) {
+	while ((c = getopt_long(argc, argv, "bcvthnwWM:T:", options, NULL)) != -1) {
 		switch (c) {
 			case 'b':
 				fprintf(stderr, "-b/--binary option is not implemented\n");
@@ -224,6 +234,12 @@ int ip6tables_restore_main(int argc, char *argv[])
 			case 'n':
 				noflush = 1;
 				break;
+			case 'w':
+				wait = parse_wait_time(argc, argv);
+				break;
+			case 'W':
+				parse_wait_interval(argc, argv, &wait_interval);
+				break;
 			case 'M':
 				xtables_modprobe_program = optarg;
 				break;
@@ -268,8 +284,23 @@ int ip6tables_restore_main(int argc, char *argv[])
 				DEBUGP("Not calling commit, testing\n");
 				ret = 1;
 			}
+
+			/* Done with the current table, release the lock. */
+			if (lock >= 0) {
+				xtables_unlock(lock);
+				lock = XT_LOCK_NOT_ACQUIRED;
+			}
+
 			in_table = 0;
 		} else if ((buffer[0] == '*') && (!in_table)) {
+			/* Acquire a lock before we create a new table handle */
+			lock = xtables_lock(wait, &wait_interval);
+			if (lock == XT_LOCK_BUSY) {
+				fprintf(stderr, "Another app is currently holding the xtables lock. "
+					"Perhaps you want to use the -w option?\n");
+				exit(RESOURCE_PROBLEM);
+			}
+
 			/* New table */
 			char *table;
 
diff --git a/iptables/ip6tables.c b/iptables/ip6tables.c
index 4d77721b04..579d347b09 100644
--- a/iptables/ip6tables.c
+++ b/iptables/ip6tables.c
@@ -1779,7 +1779,7 @@ int do_command6(int argc, char *argv[], char **table,
 	generic_opt_check(command, cs.options);
 
 	/* Attempt to acquire the xtables lock */
-	if (!restore && !xtables_lock(wait, &wait_interval)) {
+	if (!restore && xtables_lock(wait, &wait_interval) == XT_LOCK_BUSY) {
 		fprintf(stderr, "Another app is currently holding the xtables lock. ");
 		if (wait == 0)
 			fprintf(stderr, "Perhaps you want to use the -w option?\n");
diff --git a/iptables/iptables-restore.c b/iptables/iptables-restore.c
index 2f1522db52..7bb06d84b1 100644
--- a/iptables/iptables-restore.c
+++ b/iptables/iptables-restore.c
@@ -12,6 +12,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "iptables.h"
+#include "xshared.h"
 #include "xtables.h"
 #include "libiptc/libiptc.h"
 #include "iptables-multi.h"
@@ -22,17 +23,23 @@
 #define DEBUGP(x, args...)
 #endif
 
-static int counters = 0, verbose = 0, noflush = 0;
+static int counters = 0, verbose = 0, noflush = 0, wait = 0;
+
+static struct timeval wait_interval = {
+	.tv_sec	= 1,
+};
 
 /* Keeping track of external matches and targets.  */
 static const struct option options[] = {
-	{.name = "counters", .has_arg = false, .val = 'c'},
-	{.name = "verbose",  .has_arg = false, .val = 'v'},
-	{.name = "test",     .has_arg = false, .val = 't'},
-	{.name = "help",     .has_arg = false, .val = 'h'},
-	{.name = "noflush",  .has_arg = false, .val = 'n'},
-	{.name = "modprobe", .has_arg = true,  .val = 'M'},
-	{.name = "table",    .has_arg = true,  .val = 'T'},
+	{.name = "counters",      .has_arg = 0, .val = 'c'},
+	{.name = "verbose",       .has_arg = 0, .val = 'v'},
+	{.name = "test",          .has_arg = 0, .val = 't'},
+	{.name = "help",          .has_arg = 0, .val = 'h'},
+	{.name = "noflush",       .has_arg = 0, .val = 'n'},
+	{.name = "modprobe",      .has_arg = 1, .val = 'M'},
+	{.name = "table",         .has_arg = 1, .val = 'T'},
+	{.name = "wait",          .has_arg = 2, .val = 'w'},
+	{.name = "wait-interval", .has_arg = 2, .val = 'W'},
 	{NULL},
 };
 
@@ -42,14 +49,16 @@ static void print_usage(const char *name, const char *version) __attribute__((no
 
 static void print_usage(const char *name, const char *version)
 {
-	fprintf(stderr, "Usage: %s [-c] [-v] [-t] [-h] [-n] [-T table] [-M command]\n"
+	fprintf(stderr, "Usage: %s [-c] [-v] [-t] [-h] [-n] [-w secs] [-W usecs] [-T table] [-M command]\n"
 			"	   [ --counters ]\n"
 			"	   [ --verbose ]\n"
 			"	   [ --test ]\n"
 			"	   [ --help ]\n"
 			"	   [ --noflush ]\n"
+			"	   [ --wait=<seconds>\n"
+			"	   [ --wait-interval=<usecs>\n"
 			"	   [ --table=<TABLE> ]\n"
-			"          [ --modprobe=<command> ]\n", name);
+			"	   [ --modprobe=<command> ]\n", name);
 
 	exit(1);
 }
@@ -180,7 +189,7 @@ iptables_restore_main(int argc, char *argv[])
 {
 	struct xtc_handle *handle = NULL;
 	char buffer[10240];
-	int c;
+	int c, lock;
 	char curtable[XT_TABLE_MAXNAMELEN + 1];
 	FILE *in;
 	int in_table = 0, testing = 0;
@@ -188,6 +197,7 @@ iptables_restore_main(int argc, char *argv[])
 	const struct xtc_ops *ops = &iptc_ops;
 
 	line = 0;
+	lock = XT_LOCK_NOT_ACQUIRED;
 
 	iptables_globals.program_name = "iptables-restore";
 	c = xtables_init_all(&iptables_globals, NFPROTO_IPV4);
@@ -202,7 +212,7 @@ iptables_restore_main(int argc, char *argv[])
 	init_extensions4();
 #endif
 
-	while ((c = getopt_long(argc, argv, "bcvthnM:T:", options, NULL)) != -1) {
+	while ((c = getopt_long(argc, argv, "bcvthnwWM:T:", options, NULL)) != -1) {
 		switch (c) {
 			case 'b':
 				fprintf(stderr, "-b/--binary option is not implemented\n");
@@ -223,6 +233,12 @@ iptables_restore_main(int argc, char *argv[])
 			case 'n':
 				noflush = 1;
 				break;
+			case 'w':
+				wait = parse_wait_time(argc, argv);
+				break;
+			case 'W':
+				parse_wait_interval(argc, argv, &wait_interval);
+				break;
 			case 'M':
 				xtables_modprobe_program = optarg;
 				break;
@@ -267,8 +283,23 @@ iptables_restore_main(int argc, char *argv[])
 				DEBUGP("Not calling commit, testing\n");
 				ret = 1;
 			}
+
+			/* Done with the current table, release the lock. */
+			if (lock >= 0) {
+				xtables_unlock(lock);
+				lock = XT_LOCK_NOT_ACQUIRED;
+			}
+
 			in_table = 0;
 		} else if ((buffer[0] == '*') && (!in_table)) {
+			/* Acquire a lock before we create a new table handle */
+			lock = xtables_lock(wait, &wait_interval);
+			if (lock == XT_LOCK_BUSY) {
+				fprintf(stderr, "Another app is currently holding the xtables lock. "
+					"Perhaps you want to use the -w option?\n");
+				exit(RESOURCE_PROBLEM);
+			}
+
 			/* New table */
 			char *table;
 
diff --git a/iptables/iptables.c b/iptables/iptables.c
index 04be5abb10..62731c5ebb 100644
--- a/iptables/iptables.c
+++ b/iptables/iptables.c
@@ -1766,7 +1766,7 @@ int do_command4(int argc, char *argv[], char **table,
 	generic_opt_check(command, cs.options);
 
 	/* Attempt to acquire the xtables lock */
-	if (!restore && !xtables_lock(wait, &wait_interval)) {
+	if (!restore && xtables_lock(wait, &wait_interval) == XT_LOCK_BUSY) {
 		fprintf(stderr, "Another app is currently holding the xtables lock. ");
 		if (wait == 0)
 			fprintf(stderr, "Perhaps you want to use the -w option?\n");
diff --git a/iptables/xshared.c b/iptables/xshared.c
index dd5f8be028..5a7fcc0046 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -245,7 +245,7 @@ void xs_init_match(struct xtables_match *match)
 		match->init(match->m);
 }
 
-bool xtables_lock(int wait, struct timeval *wait_interval)
+int xtables_lock(int wait, struct timeval *wait_interval)
 {
 	struct timeval time_left, wait_time;
 	int fd, i = 0;
@@ -255,22 +255,22 @@ bool xtables_lock(int wait, struct timeval *wait_interval)
 
 	fd = open(XT_LOCK_NAME, O_CREAT, 0600);
 	if (fd < 0)
-		return true;
+		return XT_LOCK_UNSUPPORTED;
 
 	if (wait == -1) {
 		if (flock(fd, LOCK_EX) == 0)
-			return true;
+			return fd;
 
 		fprintf(stderr, "Can't lock %s: %s\n", XT_LOCK_NAME,
 			strerror(errno));
-		return false;
+		return XT_LOCK_BUSY;
 	}
 
 	while (1) {
 		if (flock(fd, LOCK_EX | LOCK_NB) == 0)
-			return true;
+			return fd;
 		else if (timercmp(&time_left, wait_interval, <))
-			return false;
+			return XT_LOCK_BUSY;
 
 		if (++i % 10 == 0) {
 			fprintf(stderr, "Another app is currently holding the xtables lock; "
@@ -284,6 +284,12 @@ bool xtables_lock(int wait, struct timeval *wait_interval)
 	}
 }
 
+void xtables_unlock(int lock)
+{
+	if (lock >= 0)
+		close(lock);
+}
+
 int parse_wait_time(int argc, char *argv[])
 {
 	int wait = -1;
diff --git a/iptables/xshared.h b/iptables/xshared.h
index d8a697ae66..539e6c243b 100644
--- a/iptables/xshared.h
+++ b/iptables/xshared.h
@@ -86,7 +86,28 @@ extern struct xtables_match *load_proto(struct iptables_command_state *);
 extern int subcmd_main(int, char **, const struct subcommand *);
 extern void xs_init_target(struct xtables_target *);
 extern void xs_init_match(struct xtables_match *);
-bool xtables_lock(int wait, struct timeval *wait_interval);
+
+/**
+ * Values for the iptables lock.
+ *
+ * A value >= 0 indicates the lock filedescriptor. Other values are:
+ *
+ * XT_LOCK_UNSUPPORTED : The system does not support locking, execution will
+ * proceed lockless.
+ *
+ * XT_LOCK_BUSY : The lock was held by another process. xtables_lock only
+ * returns this value when |wait| == false. If |wait| == true, xtables_lock
+ * will not return unless the lock has been acquired.
+ *
+ * XT_LOCK_NOT_ACQUIRED : We have not yet attempted to acquire the lock.
+ */
+enum {
+	XT_LOCK_BUSY = -1,
+	XT_LOCK_UNSUPPORTED  = -2,
+	XT_LOCK_NOT_ACQUIRED  = -3,
+};
+extern int xtables_lock(int wait, struct timeval *tv);
+extern void xtables_unlock(int lock);
 
 int parse_wait_time(int argc, char *argv[]);
 void parse_wait_interval(int argc, char *argv[], struct timeval *wait_interval);
-- 
2.12.0.367.g23dc2f6d3c-goog

Re: [PATCH iptables v2 1/2] iptables: remove duplicated argument parsing code

[Pablo Neira Ayuso]

On Thu, Mar 16, 2017 at 04:55:01PM +0900, Lorenzo Colitti wrote:
> 1. Factor out repeated code to a new xs_has_arg function.
> 2. Add a new parse_wait_time option to parse the value of -w.
> 3. Make parse_wait_interval take argc and argv so its callers
>    can be simpler.

Also applied, thanks Lorenzo.

Re: [PATCH iptables v2 2/2] iptables-restore: support acquiring the lock.

[Pablo Neira Ayuso]

Hi Lorenzo,

On Thu, Mar 16, 2017 at 04:55:02PM +0900, Lorenzo Colitti wrote:
> Currently, ip[6]tables-restore does not perform any locking, so it
> is not safe to use concurrently with ip[6]tables.
> 
> This patch makes ip[6]tables-restore wait for the lock if -w
> was specified. Arguments to -w and -W are supported in the same
> was as they are in ip[6]tables.
> 
> The lock is not acquired on startup. Instead, it is acquired when
> a new table handle is created (on encountering '*') and released
> when the table is committed (COMMIT). This makes it possible to
> keep long-running iptables-restore processes in the background
> (for example, reading commands from a pipe opened by a system
> management daemon) and simultaneously run iptables commands.
> 
> If -w is not specified, then the command proceeds without taking
> the lock.
> 
> Tested as follows:
> 
> 1. Run iptables-restore -w, and check that iptables commands work
>    with or without -w.
> 2. Type "*filter" into the iptables-restore input. Verify that
>    a) ip[6]tables commands without -w fail with "another app is
>       currently holding the xtables lock...".
>    b) ip[6]tables commands with "-w 2" fail after 2 seconds.
>    c) ip[6]tables commands with "-w" hang until "COMMIT" is
>       typed into the iptables-restore window.
> 3. With the lock held by an ip6tables-restore process:
>      strace -e flock /tmp/iptables/sbin/iptables-restore -w 1 -W 100000
>    shows 11 calls to flock and fails.
> 4. Run an iptables-restore with -w and one without -w, and check:
>    a) Type "*filter" in the first and then the second, and the
>       second exits with an error.
>    b) Type "*filter" in the second and "*filter" "-S" "COMMIT"
>       into the first. The rules are listed only when the first
>       copy sees "COMMIT".

My concern with this is that one iptables-restore instance may
postpone any other iptables call indefinitely, by simply typing
"*filter" with no COMMIT ever.

The other instance can simply kill this process, as they would be both
running with CAP_NET_ADMIN though.

Re: [PATCH iptables v2 2/2] iptables-restore: support acquiring the lock.

[Lorenzo Colitti]

On Fri, Mar 17, 2017 at 10:20 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> My concern with this is that one iptables-restore instance may
> postpone any other iptables call indefinitely, by simply typing
> "*filter" with no COMMIT ever.

True. But unless the command is run with just plain "-w" (i.e., wait
forever with no timeout) then the user will get an error message that
the lock is held and can take action.

Also: are you thinking about a misconfiguration or an error in a
script, or malicious behaviour? A malicious actor can already block
any iptables commands in the same way by running "flock -e
/run/iptables.lock cat".

Re: [PATCH iptables v2 2/2] iptables-restore: support acquiring the lock.

[Pablo Neira Ayuso]

On Thu, Mar 16, 2017 at 04:55:02PM +0900, Lorenzo Colitti wrote:
> Currently, ip[6]tables-restore does not perform any locking, so it
> is not safe to use concurrently with ip[6]tables.
> 
> This patch makes ip[6]tables-restore wait for the lock if -w
> was specified. Arguments to -w and -W are supported in the same
> was as they are in ip[6]tables.
> 
> The lock is not acquired on startup. Instead, it is acquired when
> a new table handle is created (on encountering '*') and released
> when the table is committed (COMMIT). This makes it possible to
> keep long-running iptables-restore processes in the background
> (for example, reading commands from a pipe opened by a system
> management daemon) and simultaneously run iptables commands.
> 
> If -w is not specified, then the command proceeds without taking
> the lock.
> 
> Tested as follows:
> 
> 1. Run iptables-restore -w, and check that iptables commands work
>    with or without -w.
> 2. Type "*filter" into the iptables-restore input. Verify that
>    a) ip[6]tables commands without -w fail with "another app is
>       currently holding the xtables lock...".
>    b) ip[6]tables commands with "-w 2" fail after 2 seconds.
>    c) ip[6]tables commands with "-w" hang until "COMMIT" is
>       typed into the iptables-restore window.
> 3. With the lock held by an ip6tables-restore process:
>      strace -e flock /tmp/iptables/sbin/iptables-restore -w 1 -W 100000
>    shows 11 calls to flock and fails.
> 4. Run an iptables-restore with -w and one without -w, and check:
>    a) Type "*filter" in the first and then the second, and the
>       second exits with an error.
>    b) Type "*filter" in the second and "*filter" "-S" "COMMIT"
>       into the first. The rules are listed only when the first
>       copy sees "COMMIT".

Applied, thanks Lorenzo.