Merge branch 'net-af_packet-allow-joining-a-fanout-when-link-is-down'

Gur Stavi says:

====================
net: af_packet: allow joining a fanout when link is down

PACKET socket can retain its fanout membership through link down and up
and leave a fanout while closed regardless of link state.
However, socket was forbidden from joining a fanout while it was not
RUNNING.

This scenario was identified while studying DPDK pmd_af_packet_drv.
Since sockets are only created during initialization, there is no reason
to fail the initialization if a single link is temporarily down.

This patch allows PACKET socket to join a fanout while not RUNNING.

Selftest psock_fanout is extended to test this "fanout while link down"
scenario.

Selftest psock_fanout is also extended to test fanout create/join by
socket that did not bind or specified a protocol, which carries an
implicit bind.

v3: https://lore.kernel.org/cover.1728555449.git.gur.stavi@huawei.com
v2: https://lore.kernel.org/cover.1728382839.git.gur.stavi@huawei.com
v1: https://lore.kernel.org/cover.1728303615.git.gur.stavi@huawei.com
====================

Link: https://patch.msgid.link/cover.1728802323.git.gur.stavi@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/packet/af_packet.c

@@ -1846,21 +1846,22 @@ static int fanout_add(struct sock *sk, struct fanout_args *args)
 	err = -EINVAL;
 
 	spin_lock(&po->bind_lock);
-	if (packet_sock_flag(po, PACKET_SOCK_RUNNING) &&
+	if (po->num &&
 	    match->type == type &&
 	    match->prot_hook.type == po->prot_hook.type &&
 	    match->prot_hook.dev == po->prot_hook.dev) {
 		err = -ENOSPC;
 		if (refcount_read(&match->sk_ref) < match->max_num_members) {
-			__dev_remove_pack(&po->prot_hook);
-
 			/* Paired with packet_setsockopt(PACKET_FANOUT_DATA) */
 			WRITE_ONCE(po->fanout, match);
 
 			po->rollover = rollover;
 			rollover = NULL;
 			refcount_set(&match->sk_ref, refcount_read(&match->sk_ref) + 1);
-			__fanout_link(sk, po);
+			if (packet_sock_flag(po, PACKET_SOCK_RUNNING)) {
+				__dev_remove_pack(&po->prot_hook);
+				__fanout_link(sk, po);
+			}
 			err = 0;
 		}
 	}

tools/testing/selftests/net/psock_fanout.c

@@ -48,6 +48,7 @@
 #include <string.h>
 #include <sys/mman.h>
 #include <sys/socket.h>
+#include <sys/ioctl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -59,6 +60,33 @@
 
 static uint32_t cfg_max_num_members;
 
+static void loopback_set_up_down(int state_up)
+{
+	struct ifreq ifreq = {};
+	int fd, err;
+
+	fd = socket(AF_PACKET, SOCK_RAW, 0);
+	if (fd < 0) {
+		perror("socket loopback");
+		exit(1);
+	}
+	strcpy(ifreq.ifr_name, "lo");
+	err = ioctl(fd, SIOCGIFFLAGS, &ifreq);
+	if (err) {
+		perror("SIOCGIFFLAGS");
+		exit(1);
+	}
+	if (state_up != !!(ifreq.ifr_flags & IFF_UP)) {
+		ifreq.ifr_flags ^= IFF_UP;
+		err = ioctl(fd, SIOCSIFFLAGS, &ifreq);
+		if (err) {
+			perror("SIOCSIFFLAGS");
+			exit(1);
+		}
+	}
+	close(fd);
+}
+
 /* Open a socket in a given fanout mode.
  * @return -1 if mode is bad, a valid socket otherwise */
 static int sock_fanout_open(uint16_t typeflags, uint16_t group_id)
@@ -251,6 +279,41 @@ static int sock_fanout_read(int fds[], char *rings[], const int expect[])
 	return 0;
 }
 
+/* Test that creating/joining a fanout group fails for unbound socket without
+ * a specified protocol
+ */
+static void test_unbound_fanout(void)
+{
+	int val, fd0, fd1, err;
+
+	fprintf(stderr, "test: unbound fanout\n");
+	fd0 = socket(PF_PACKET, SOCK_RAW, 0);
+	if (fd0 < 0) {
+		perror("socket packet");
+		exit(1);
+	}
+	/* Try to create a new fanout group. Should fail. */
+	val = (PACKET_FANOUT_HASH << 16) | 1;
+	err = setsockopt(fd0, SOL_PACKET, PACKET_FANOUT, &val, sizeof(val));
+	if (!err) {
+		fprintf(stderr, "ERROR: unbound socket fanout create\n");
+		exit(1);
+	}
+	fd1 = sock_fanout_open(PACKET_FANOUT_HASH, 1);
+	if (fd1 == -1) {
+		fprintf(stderr, "ERROR: failed to open HASH socket\n");
+		exit(1);
+	}
+	/* Try to join an existing fanout group. Should fail. */
+	err = setsockopt(fd0, SOL_PACKET, PACKET_FANOUT, &val, sizeof(val));
+	if (!err) {
+		fprintf(stderr, "ERROR: unbound socket fanout join\n");
+		exit(1);
+	}
+	close(fd0);
+	close(fd1);
+}
+
 /* Test illegal mode + flag combination */
 static void test_control_single(void)
 {
@@ -264,17 +327,22 @@ static void test_control_single(void)
 }
 
 /* Test illegal group with different modes or flags */
-static void test_control_group(void)
+static void test_control_group(int toggle)
 {
 	int fds[2];
 
-	fprintf(stderr, "test: control multiple sockets\n");
+	if (toggle)
+		fprintf(stderr, "test: control multiple sockets with link down toggle\n");
+	else
+		fprintf(stderr, "test: control multiple sockets\n");
 
 	fds[0] = sock_fanout_open(PACKET_FANOUT_HASH, 0);
 	if (fds[0] == -1) {
 		fprintf(stderr, "ERROR: failed to open HASH socket\n");
 		exit(1);
 	}
+	if (toggle)
+		loopback_set_up_down(0);
 	if (sock_fanout_open(PACKET_FANOUT_HASH |
 			       PACKET_FANOUT_FLAG_DEFRAG, 0) != -1) {
 		fprintf(stderr, "ERROR: joined group with wrong flag defrag\n");
@@ -294,6 +362,8 @@ static void test_control_group(void)
 		fprintf(stderr, "ERROR: failed to join group\n");
 		exit(1);
 	}
+	if (toggle)
+		loopback_set_up_down(1);
 	if (close(fds[1]) || close(fds[0])) {
 		fprintf(stderr, "ERROR: closing sockets\n");
 		exit(1);
@@ -488,8 +558,10 @@ int main(int argc, char **argv)
 	const int expect_uniqueid[2][2] = { { 20, 20},  { 20, 20 } };
 	int port_off = 2, tries = 20, ret;
 
+	test_unbound_fanout();
 	test_control_single();
-	test_control_group();
+	test_control_group(0);
+	test_control_group(1);
 	test_control_group_max_num_members();
 	test_unique_fanout_group_ids();