Merge branch 'tcp-md5-vrf-fix'

Leonard Crestez says:

====================
tcp: md5: Fix overlap between vrf and non-vrf keys

With net.ipv4.tcp_l3mdev_accept=1 it is possible for a listen socket to
accept connection from the same client address in different VRFs. It is
also possible to set different MD5 keys for these clients which differ only
in the tcpm_l3index field.

This appears to work when distinguishing between different VRFs but not
between non-VRF and VRF connections. In particular:

* tcp_md5_do_lookup_exact will match a non-vrf key against a vrf key. This
means that adding a key with l3index != 0 after a key with l3index == 0
will cause the earlier key to be deleted. Both keys can be present if the
non-vrf key is added later.
* _tcp_md5_do_lookup can match a non-vrf key before a vrf key. This casues
failures if the passwords differ.

This can be fixed by making tcp_md5_do_lookup_exact perform an actual exact
comparison on l3index and by making  __tcp_md5_do_lookup perfer vrf-bound
keys above other considerations like prefixlen.

The fact that keys with l3index==0 affect VRF connections is usually not
desirable, VRFs are meant to be completely independent. This behavior needs
to preserved for backwards compatibility. Also, applications can just bind
listen sockets to VRF and never specify TCP_MD5SIG_FLAG_IFINDEX at all.

So far the combination of TCP_MD5SIG_FLAG_IFINDEX with tcpm_ifindex == 0
was an error, accept this to mean "key only applies to default VRF". This
is what applications using VRFs for traffic separation want.

This also contains tests for the second part. It does not contain tests for
overlapping keys, that would require more changes in nettest to add
multiple keys. These scenarios are also covered by my tests for TCP-AO,
especially around this area:
https://github.com/cdleonard/tcp-authopt-test/blob/main/tcp_authopt_test/test_vrf_bind.py

Changes since V2:
* Rename --do-bind-key-ifindex to --force-bind-key-ifindex
* Fix referencing TCP_MD5SIG_FLAG_IFINDEX as TCP_MD5SIG_IFINDEX
Link to v2: https://lore.kernel.org/netdev/cover.1634107317.git.cdleonard@gmail.com/

Changes since V1:
* Accept (TCP_MD5SIG_IFINDEX with tcpm_ifindex == 0)
* Add flags for explicitly including or excluding TCP_MD5SIG_FLAG_IFINDEX
to nettest
* Add few more tests in fcnal-test.sh.
Link to v1: https://lore.kernel.org/netdev/3d8387d499f053dba5cd9184c0f7b8445c4470c6.1633542093.git.cdleonard@gmail.com/
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 86 insertions, 2 deletions

diff --git a/tools/testing/selftests/net/fcnal-test.sh b/tools/testing/selftests/net/fcnal-test.sh
index 13350cd5c8ac..8e67a252b672 100755
--- a/tools/testing/selftests/net/fcnal-test.sh
+++ b/tools/testing/selftests/net/fcnal-test.sh
@@ -289,6 +289,12 @@ set_sysctl()
 	run_cmd sysctl -q -w $*
 }
 
+# get sysctl values in NS-A
+get_sysctl()
+{
+	${NSA_CMD} sysctl -n $*
+}
+
 ################################################################################
 # Setup for tests
 
@@ -1003,6 +1009,60 @@ ipv4_tcp_md5()
 	run_cmd nettest -s -I ${NSA_DEV} -M ${MD5_PW} -m ${NS_NET}
 	log_test $? 1 "MD5: VRF: Device must be a VRF - prefix"
 
+	test_ipv4_md5_vrf__vrf_server__no_bind_ifindex
+	test_ipv4_md5_vrf__global_server__bind_ifindex0
+}
+
+test_ipv4_md5_vrf__vrf_server__no_bind_ifindex()
+{
+	log_start
+	show_hint "Simulates applications using VRF without TCP_MD5SIG_FLAG_IFINDEX"
+	run_cmd nettest -s -I ${VRF} -M ${MD5_PW} -m ${NS_NET} --no-bind-key-ifindex &
+	sleep 1
+	run_cmd_nsb nettest -r ${NSA_IP} -X ${MD5_PW}
+	log_test $? 0 "MD5: VRF: VRF-bound server, unbound key accepts connection"
+
+	log_start
+	show_hint "Binding both the socket and the key is not required but it works"
+	run_cmd nettest -s -I ${VRF} -M ${MD5_PW} -m ${NS_NET} --force-bind-key-ifindex &
+	sleep 1
+	run_cmd_nsb nettest -r ${NSA_IP} -X ${MD5_PW}
+	log_test $? 0 "MD5: VRF: VRF-bound server, bound key accepts connection"
+}
+
+test_ipv4_md5_vrf__global_server__bind_ifindex0()
+{
+	# This particular test needs tcp_l3mdev_accept=1 for Global server to accept VRF connections
+	local old_tcp_l3mdev_accept
+	old_tcp_l3mdev_accept=$(get_sysctl net.ipv4.tcp_l3mdev_accept)
+	set_sysctl net.ipv4.tcp_l3mdev_accept=1
+
+	log_start
+	run_cmd nettest -s -M ${MD5_PW} -m ${NS_NET} --force-bind-key-ifindex &
+	sleep 1
+	run_cmd_nsb nettest -r ${NSA_IP} -X ${MD5_PW}
+	log_test $? 2 "MD5: VRF: Global server, Key bound to ifindex=0 rejects VRF connection"
+
+	log_start
+	run_cmd nettest -s -M ${MD5_PW} -m ${NS_NET} --force-bind-key-ifindex &
+	sleep 1
+	run_cmd_nsc nettest -r ${NSA_IP} -X ${MD5_PW}
+	log_test $? 0 "MD5: VRF: Global server, key bound to ifindex=0 accepts non-VRF connection"
+	log_start
+
+	run_cmd nettest -s -M ${MD5_PW} -m ${NS_NET} --no-bind-key-ifindex &
+	sleep 1
+	run_cmd_nsb nettest -r ${NSA_IP} -X ${MD5_PW}
+	log_test $? 0 "MD5: VRF: Global server, key not bound to ifindex accepts VRF connection"
+
+	log_start
+	run_cmd nettest -s -M ${MD5_PW} -m ${NS_NET} --no-bind-key-ifindex &
+	sleep 1
+	run_cmd_nsc nettest -r ${NSA_IP} -X ${MD5_PW}
+	log_test $? 0 "MD5: VRF: Global server, key not bound to ifindex accepts non-VRF connection"
+
+	# restore value
+	set_sysctl net.ipv4.tcp_l3mdev_accept="$old_tcp_l3mdev_accept"
 }
 
 ipv4_tcp_novrf()
diff --git a/tools/testing/selftests/net/nettest.c b/tools/testing/selftests/net/nettest.c
index bd6288302094..b599003eb5ba 100644
--- a/tools/testing/selftests/net/nettest.c
+++ b/tools/testing/selftests/net/nettest.c
@@ -28,6 +28,7 @@
 #include <unistd.h>
 #include <time.h>
 #include <errno.h>
+#include <getopt.h>
 
 #include <linux/xfrm.h>
 #include <linux/ipsec.h>
@@ -101,6 +102,8 @@ struct sock_args {
 		struct sockaddr_in6 v6;
 	} md5_prefix;
 	unsigned int prefix_len;
+	/* 0: default, -1: force off, +1: force on */
+	int bind_key_ifindex;
 
 	/* expected addresses and device index for connection */
 	const char *expected_dev;
@@ -271,11 +274,14 @@ static int tcp_md5sig(int sd, void *addr, socklen_t alen, struct sock_args *args
 	}
 	memcpy(&md5sig.tcpm_addr, addr, alen);
 
-	if (args->ifindex) {
+	if ((args->ifindex && args->bind_key_ifindex >= 0) || args->bind_key_ifindex >= 1) {
 		opt = TCP_MD5SIG_EXT;
 		md5sig.tcpm_flags |= TCP_MD5SIG_FLAG_IFINDEX;
 
 		md5sig.tcpm_ifindex = args->ifindex;
+		log_msg("TCP_MD5SIG_FLAG_IFINDEX set tcpm_ifindex=%d\n", md5sig.tcpm_ifindex);
+	} else {
+		log_msg("TCP_MD5SIG_FLAG_IFINDEX off\n", md5sig.tcpm_ifindex);
 	}
 
 	rc = setsockopt(sd, IPPROTO_TCP, opt, &md5sig, sizeof(md5sig));
@@ -1822,6 +1828,14 @@ static int ipc_parent(int cpid, int fd, struct sock_args *args)
 }
 
 #define GETOPT_STR  "sr:l:c:p:t:g:P:DRn:M:X:m:d:I:BN:O:SCi6xL:0:1:2:3:Fbq"
+#define OPT_FORCE_BIND_KEY_IFINDEX 1001
+#define OPT_NO_BIND_KEY_IFINDEX 1002
+
+static struct option long_opts[] = {
+	{"force-bind-key-ifindex", 0, 0, OPT_FORCE_BIND_KEY_IFINDEX},
+	{"no-bind-key-ifindex", 0, 0, OPT_NO_BIND_KEY_IFINDEX},
+	{0, 0, 0, 0}
+};
 
 static void print_usage(char *prog)
 {
@@ -1858,6 +1872,10 @@ static void print_usage(char *prog)
 	"    -M password   use MD5 sum protection\n"
 	"    -X password   MD5 password for client mode\n"
 	"    -m prefix/len prefix and length to use for MD5 key\n"
+	"    --no-bind-key-ifindex: Force TCP_MD5SIG_FLAG_IFINDEX off\n"
+	"    --force-bind-key-ifindex: Force TCP_MD5SIG_FLAG_IFINDEX on\n"
+	"        (default: only if -I is passed)\n"
+	"\n"
 	"    -g grp        multicast group (e.g., 239.1.1.1)\n"
 	"    -i            interactive mode (default is echo and terminate)\n"
 	"\n"
@@ -1893,7 +1911,7 @@ int main(int argc, char *argv[])
 	 * process input args
 	 */
 
-	while ((rc = getopt(argc, argv, GETOPT_STR)) != -1) {
+	while ((rc = getopt_long(argc, argv, GETOPT_STR, long_opts, NULL)) != -1) {
 		switch (rc) {
 		case 'B':
 			both_mode = 1;
@@ -1966,6 +1984,12 @@ int main(int argc, char *argv[])
 		case 'M':
 			args.password = optarg;
 			break;
+		case OPT_FORCE_BIND_KEY_IFINDEX:
+			args.bind_key_ifindex = 1;
+			break;
+		case OPT_NO_BIND_KEY_IFINDEX:
+			args.bind_key_ifindex = -1;
+			break;
 		case 'X':
 			args.client_pw = optarg;
 			break;