netdev - [PATCH iproute2 v2] ip: drop 2-char command assumption

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Date:   Tue, 20 Apr 2021 01:26:36 -0700
From:   Tony Ambardar <tony.ambardar@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        David Ahern <dsahern@...il.com>
Cc:     Tony Ambardar <Tony.Ambardar@...il.com>, netdev@...r.kernel.org
Subject: [PATCH iproute2 v2] ip: drop 2-char command assumption

The 'ip' utility hardcodes the assumption of being a 2-char command, where
any follow-on characters are passed as an argument:

  $ ./ip-full help
  Object "-full" is unknown, try "ip help".

This confusing behaviour isn't seen with 'tc' for example, and was added in
a 2005 commit without documentation. It was noticed during testing of 'ip'
variants built/packaged with different feature sets (e.g. w/o BPF support).

Mitigate the problem by redoing the command without the 2-char assumption
if the follow-on characters fail to parse as a valid command.

Fixes: 351efcde4e62 ("Update header files to 2.6.14")
Signed-off-by: Tony Ambardar <Tony.Ambardar@...il.com>
---
v2: (feedback from David Ahern)
  * work around problem but remain compatible with 2-char assumption

---
 ip/ip.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/ip/ip.c b/ip/ip.c
index 4cf09fc3..8e4c6eb5 100644
--- a/ip/ip.c
+++ b/ip/ip.c
@@ -125,7 +125,7 @@ static const struct cmd {
 	{ 0 }
 };
 
-static int do_cmd(const char *argv0, int argc, char **argv)
+static int do_cmd(const char *argv0, int argc, char **argv, bool final)
 {
 	const struct cmd *c;
 
@@ -134,7 +134,8 @@ static int do_cmd(const char *argv0, int argc, char **argv)
 			return -(c->func(argc-1, argv+1));
 	}
 
-	fprintf(stderr, "Object \"%s\" is unknown, try \"ip help\".\n", argv0);
+	if (final)
+		fprintf(stderr, "Object \"%s\" is unknown, try \"ip help\".\n", argv0);
 	return EXIT_FAILURE;
 }
 
@@ -143,7 +144,7 @@ static int ip_batch_cmd(int argc, char *argv[], void *data)
 	const int *orig_family = data;
 
 	preferred_family = *orig_family;
-	return do_cmd(argv[0], argc, argv);
+	return do_cmd(argv[0], argc, argv, true);
 }
 
 static int batch(const char *name)
@@ -313,11 +314,14 @@ int main(int argc, char **argv)
 
 	rtnl_set_strict_dump(&rth);
 
-	if (strlen(basename) > 2)
-		return do_cmd(basename+2, argc, argv);
+	if (strlen(basename) > 2) {
+		int ret = do_cmd(basename+2, argc, argv, false);
+		if (ret != EXIT_FAILURE)
+			return ret;
+	}
 
 	if (argc > 1)
-		return do_cmd(argv[1], argc-1, argv+1);
+		return do_cmd(argv[1], argc-1, argv+1, true);
 
 	rtnl_close(&rth);
 	usage();
-- 
2.25.1