netdev - [PATCH] iproute2: ip maddress: Check multiaddr length

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Date:   Fri, 14 Aug 2020 10:46:26 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     kernel@...gutronix.de, Sascha Hauer <s.hauer@...gutronix.de>
Subject: [PATCH] iproute2: ip maddress: Check multiaddr length

ip maddress add|del takes a MAC address as argument, so insist on
getting a length of ETH_ALEN bytes. This makes sure the passed argument
is actually a MAC address and especially not an IPv4 address which
was previously accepted and silently taken as a MAC address.

While at it, do not print *argv in the error path as this has been
modified by ll_addr_a2n() and doesn't contain the full string anymore,
which can lead to misleading error messages.

Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
---
 ip/ipmaddr.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/ip/ipmaddr.c b/ip/ipmaddr.c
index 3400e055..9979ed58 100644
--- a/ip/ipmaddr.c
+++ b/ip/ipmaddr.c
@@ -291,7 +291,7 @@ static int multiaddr_modify(int cmd, int argc, char **argv)
 {
 	struct ifreq ifr = {};
 	int family;
-	int fd;
+	int fd, len;
 
 	if (cmd == RTM_NEWADDR)
 		cmd = SIOCADDMULTI;
@@ -313,9 +313,12 @@ static int multiaddr_modify(int cmd, int argc, char **argv)
 				usage();
 			if (ifr.ifr_hwaddr.sa_data[0])
 				duparg("address", *argv);
-			if (ll_addr_a2n(ifr.ifr_hwaddr.sa_data,
-					14, *argv) < 0) {
-				fprintf(stderr, "Error: \"%s\" is not a legal ll address.\n", *argv);
+			len = ll_addr_a2n(ifr.ifr_hwaddr.sa_data, 14, *argv);
+			if (len < 0)
+				exit(1);
+
+			if (len != ETH_ALEN) {
+				fprintf(stderr, "Error: Invalid address length %d - must be %d bytes\n", len, ETH_ALEN);
 				exit(1);
 			}
 		}
-- 
2.28.0