Re: [PATCH 2/8] conf: Use "-D none" and "-S none" instead of missing empty option arguments

[Stefano Brivio <sbrivio@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 5288 bytes --]

On Fri, 26 Aug 2022 14:58:33 +1000
David Gibson <david(a)gibson.dropbear.id.au> wrote:

> Both the -D (--dns) and -S (--search) options take an optional argument.
> If the argument is omitted the option is disabled entirely.  However,
> handling the optional argument requires some ugly special case handling if
> it's the last option on the command line, and has potential ambiguity with
> non-option arguments used with pasta.  It can also make it more confusing
> to read command lines.
> 
> Simplify the logic here by replacing the non-argument versions with an
> explicit "-D none" or "-S none".
> 
> Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
> ---
>  conf.c  | 18 ++++--------------
>  passt.1 |  7 ++++---
>  2 files changed, 8 insertions(+), 17 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 4eb9e3d..6770be9 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -1022,8 +1022,8 @@ void conf(struct ctx *c, int argc, char **argv)
>  		{"mac-addr",	required_argument,	NULL,		'M' },
>  		{"gateway",	required_argument,	NULL,		'g' },
>  		{"interface",	required_argument,	NULL,		'i' },
> -		{"dns",		optional_argument,	NULL,		'D' },
> -		{"search",	optional_argument,	NULL,		'S' },
> +		{"dns",		required_argument,	NULL,		'D' },
> +		{"search",	required_argument,	NULL,		'S' },
>  		{"no-tcp",	no_argument,		&c->no_tcp,	1 },
>  		{"no-udp",	no_argument,		&c->no_udp,	1 },
>  		{"no-icmp",	no_argument,		&c->no_icmp,	1 },
> @@ -1077,16 +1077,6 @@ void conf(struct ctx *c, int argc, char **argv)
>  
>  		name = getopt_long(argc, argv, optstring, options, NULL);
>  
> -		if ((name == 'D' || name == 'S') && !optarg &&
> -		    optind < argc && *argv[optind] && *argv[optind] != '-') {
> -			if (c->mode == MODE_PASTA) {
> -				if (conf_ns_opt(c, nsdir, userns, argv[optind]))
> -					optarg = argv[optind++];
> -			} else {
> -				optarg = argv[optind++];
> -			}
> -		}
> -
>  		switch (name) {
>  		case -1:
>  		case 0:
> @@ -1403,7 +1393,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  				usage(argv[0]);
>  			}
>  
> -			if (!optarg) {
> +			if (!strcmp(optarg, "none")) {
>  				c->no_dns = 1;
>  				break;
>  			}
> @@ -1430,7 +1420,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  				usage(argv[0]);
>  			}
>  
> -			if (!optarg) {
> +			if (!strcmp(optarg, "none")) {
>  				c->no_dns_search = 1;
>  				break;
>  			}

For these two hunks, clang-tidy reported something I missed in my
review:

/home/sbrivio/passt/conf.c:1417:9: error: Null pointer passed to 1st parameter expecting 'nonnull' [clang-analyzer-core.NonNullParamChecker,-warnings-as-errors]
                        if (!strcmp(optarg, "none")) {
                             ^      ~~~~~~
[...]

/home/sbrivio/passt/conf.c:1411:8: note: Assuming field 'no_dns' is 0
                        if (c->no_dns ||
                            ^~~~~~~~~
/home/sbrivio/passt/conf.c:1411:8: note: Left side of '||' is false
/home/sbrivio/passt/conf.c:1412:9: note: Assuming 'optarg' is null
                            (!optarg && (dns4 - c->ip4.dns || dns6 - c->ip6.dns))) {
                             ^~~~~~~
/home/sbrivio/passt/conf.c:1412:9: note: Left side of '&&' is true
/home/sbrivio/passt/conf.c:1412:21: note: Left side of '||' is false
                            (!optarg && (dns4 - c->ip4.dns || dns6 - c->ip6.dns))) {

...the validation logic needs to be updated here. I'm taking the
liberty of fixing this up on merge, with this diff on top:

diff --git a/conf.c b/conf.c
index 162c2dd..e6d1c62 100644
--- a/conf.c
+++ b/conf.c
@@ -1408,17 +1408,26 @@ void conf(struct ctx *c, int argc, char **argv)
 			}
 			break;
 		case 'D':
-			if (c->no_dns ||
-			    (!optarg && (dns4 - c->ip4.dns || dns6 - c->ip6.dns))) {
-				err("Empty and non-empty DNS options given");
-				usage(argv[0]);
-			}
-
 			if (!strcmp(optarg, "none")) {
+				if (c->no_dns) {
+					err("Redundant DNS options");
+					usage(argv[0]);
+				}
+
+				if (dns4 - c->ip4.dns || dns6 - c->ip6.dns) {
+					err("Conflicting DNS options");
+					usage(argv[0]);
+				}
+
 				c->no_dns = 1;
 				break;
 			}
 
+			if (c->no_dns) {
+				err("Conflicting DNS options");
+				usage(argv[0]);
+			}
+
 			if (dns4 - &c->ip4.dns[0] < ARRAY_SIZE(c->ip4.dns) &&
 			    inet_pton(AF_INET, optarg, dns4)) {
 				dns4++;
@@ -1435,17 +1444,26 @@ void conf(struct ctx *c, int argc, char **argv)
 			usage(argv[0]);
 			break;
 		case 'S':
-			if (c->no_dns_search ||
-			    (!optarg && dnss != c->dns_search)) {
-				err("Empty and non-empty DNS search given");
-				usage(argv[0]);
-			}
-
 			if (!strcmp(optarg, "none")) {
+				if (c->no_dns_search) {
+					err("Redundant DNS search options");
+					usage(argv[0]);
+				}
+
+				if (dnss != c->dns_search) {
+					err("Conflicting DNS search options");
+					usage(argv[0]);
+				}
+
 				c->no_dns_search = 1;
 				break;
 			}
 
+			if (c->no_dns_search) {
+				err("Conflicting DNS search options");
+				usage(argv[0]);
+			}
+
 			if (dnss - c->dns_search < ARRAY_SIZE(c->dns_search)) {
 				ret = snprintf(dnss->n, sizeof(*c->dns_search),
 					       "%s", optarg);


-- 
@@ -1408,17 +1408,26 @@ void conf(struct ctx *c, int argc, char **argv)
 			}
 			break;
 		case 'D':
-			if (c->no_dns ||
-			    (!optarg && (dns4 - c->ip4.dns || dns6 - c->ip6.dns))) {
-				err("Empty and non-empty DNS options given");
-				usage(argv[0]);
-			}
-
 			if (!strcmp(optarg, "none")) {
+				if (c->no_dns) {
+					err("Redundant DNS options");
+					usage(argv[0]);
+				}
+
+				if (dns4 - c->ip4.dns || dns6 - c->ip6.dns) {
+					err("Conflicting DNS options");
+					usage(argv[0]);
+				}
+
 				c->no_dns = 1;
 				break;
 			}
 
+			if (c->no_dns) {
+				err("Conflicting DNS options");
+				usage(argv[0]);
+			}
+
 			if (dns4 - &c->ip4.dns[0] < ARRAY_SIZE(c->ip4.dns) &&
 			    inet_pton(AF_INET, optarg, dns4)) {
 				dns4++;
@@ -1435,17 +1444,26 @@ void conf(struct ctx *c, int argc, char **argv)
 			usage(argv[0]);
 			break;
 		case 'S':
-			if (c->no_dns_search ||
-			    (!optarg && dnss != c->dns_search)) {
-				err("Empty and non-empty DNS search given");
-				usage(argv[0]);
-			}
-
 			if (!strcmp(optarg, "none")) {
+				if (c->no_dns_search) {
+					err("Redundant DNS search options");
+					usage(argv[0]);
+				}
+
+				if (dnss != c->dns_search) {
+					err("Conflicting DNS search options");
+					usage(argv[0]);
+				}
+
 				c->no_dns_search = 1;
 				break;
 			}
 
+			if (c->no_dns_search) {
+				err("Conflicting DNS search options");
+				usage(argv[0]);
+			}
+
 			if (dnss - c->dns_search < ARRAY_SIZE(c->dns_search)) {
 				ret = snprintf(dnss->n, sizeof(*c->dns_search),
 					       "%s", optarg);


-- 
Stefano