Exercise the scenario described in detail in the cover letter: 1) socket A: connect() from ephemeral port X 2) socket B: explicitly bind() to port X 3) check that port X is now excluded from ephemeral ports 4) close socket B to release the port bind 5) socket C: connect() from ephemeral port X Signed-off-by: Jakub Sitnicki --- tools/testing/selftests/net/Makefile | 1 + tools/testing/selftests/net/tcp_port_share.c | 182 +++++++++++++++++++++++++++ 2 files changed, 183 insertions(+) diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile index b31a71f2b372..b317ec5e6aec 100644 --- a/tools/testing/selftests/net/Makefile +++ b/tools/testing/selftests/net/Makefile @@ -117,6 +117,7 @@ TEST_GEN_FILES += tfo TEST_PROGS += tfo_passive.sh TEST_PROGS += broadcast_pmtu.sh TEST_PROGS += ipv6_force_forwarding.sh +TEST_GEN_PROGS += tcp_port_share # YNL files, must be before "include ..lib.mk" YNL_GEN_FILES := busy_poller netlink-dumps diff --git a/tools/testing/selftests/net/tcp_port_share.c b/tools/testing/selftests/net/tcp_port_share.c new file mode 100644 index 000000000000..d6db89affbc9 --- /dev/null +++ b/tools/testing/selftests/net/tcp_port_share.c @@ -0,0 +1,182 @@ +// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause +// Copyright (c) 2025 Cloudflare, Inc. + +/* Tests for TCP port sharing (bind bucket reuse). */ + +#include +#include +#include +#include +#include +#include + +#include "../kselftest_harness.h" + +struct sockaddr_inet { + union { + struct sockaddr_storage ss; + struct sockaddr_in6 v6; + struct sockaddr_in v4; + struct sockaddr sa; + }; + socklen_t len; + char str[INET6_ADDRSTRLEN + __builtin_strlen("[]:65535") + 1]; +}; + +static void make_inet_addr(int af, const char *ip, __u16 port, + struct sockaddr_inet *addr) +{ + const char *fmt = ""; + + memset(addr, 0, sizeof(*addr)); + + switch (af) { + case AF_INET: + addr->len = sizeof(addr->v4); + addr->v4.sin_family = af; + addr->v4.sin_port = htons(port); + inet_pton(af, ip, &addr->v4.sin_addr); + fmt = "%s:%hu"; + break; + case AF_INET6: + addr->len = sizeof(addr->v6); + addr->v6.sin6_family = af; + addr->v6.sin6_port = htons(port); + inet_pton(af, ip, &addr->v6.sin6_addr); + fmt = "[%s]:%hu"; + break; + } + + snprintf(addr->str, sizeof(addr->str), fmt, ip, port); +} + +static int getsockname_port(int fd) +{ + struct sockaddr_inet addr = {}; + int err; + + addr.len = sizeof(addr); + err = getsockname(fd, &addr.sa, &addr.len); + if (err) + return -1; + + switch (addr.sa.sa_family) { + case AF_INET: + return ntohs(addr.v4.sin_port); + case AF_INET6: + return ntohs(addr.v6.sin6_port); + default: + errno = EAFNOSUPPORT; + return -1; + } +} + +FIXTURE(tcp_port_share) {}; + +FIXTURE_VARIANT(tcp_port_share) { + int domain; + /* IP to listen on and connect to */ + const char *dst_ip; + /* Primary IP to connect from */ + const char *src1_ip; + /* Secondary IP to connect from */ + const char *src2_ip; + /* IP to bind to to block the source port */ + const char *bind_ip; +}; + +#define DST_PORT 30000 +#define SRC_PORT 40000 + +FIXTURE_VARIANT_ADD(tcp_port_share, ipv4) { + .domain = AF_INET, + .dst_ip = "127.0.0.1", + .src1_ip = "127.1.1.1", + .src2_ip = "127.2.2.2", + .bind_ip = "127.3.3.3", +}; + +FIXTURE_VARIANT_ADD(tcp_port_share, ipv6) { + .domain = AF_INET6, + .dst_ip = "::1", + .src1_ip = "2001:db8::1", + .src2_ip = "2001:db8::2", + .bind_ip = "2001:db8::3", +}; + +FIXTURE_SETUP(tcp_port_share) +{ + ASSERT_EQ(unshare(CLONE_NEWNET), 0); + ASSERT_EQ(system("ip link set dev lo up"), 0); + ASSERT_EQ(system("ip addr add dev lo 2001:db8::1/32 nodad"), 0); + ASSERT_EQ(system("ip addr add dev lo 2001:db8::2/32 nodad"), 0); + ASSERT_EQ(system("ip addr add dev lo 2001:db8::3/32 nodad"), 0); + ASSERT_EQ(system("sysctl -wq net.ipv4.ip_local_port_range='40000 40000'"), 0); +} + +FIXTURE_TEARDOWN(tcp_port_share) {} + +/* Check that an ephemeral port can be used again as soon as the socket bound to + * the port, blocking it from reuse, releases it. + */ +TEST_F(tcp_port_share, can_reuse_port_after_unbind) +{ + const typeof(variant) v = variant; + int c1, c2, ln, port_block; + struct sockaddr_inet addr; + const int one = 1; + + /* Listen on : */ + ln = socket(v->domain, SOCK_STREAM, 0); + ASSERT_GE(ln, 0) TH_LOG("socket(): %m"); + ASSERT_EQ(setsockopt(ln, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)), 0); + + make_inet_addr(v->domain, v->dst_ip, DST_PORT, &addr); + ASSERT_EQ(bind(ln, &addr.sa, addr.len), 0) TH_LOG("bind(%s): %m", addr.str); + ASSERT_EQ(listen(ln, 2), 0); + + /* Connect from : */ + c1 = socket(v->domain, SOCK_STREAM, 0); + ASSERT_GE(c1, 0) TH_LOG("socket(): %m"); + ASSERT_EQ(setsockopt(c1, SOL_IP, IP_BIND_ADDRESS_NO_PORT, &one, sizeof(one)), 0); + + make_inet_addr(v->domain, v->src1_ip, 0, &addr); + ASSERT_EQ(bind(c1, &addr.sa, addr.len), 0) TH_LOG("bind(%s): %m", addr.str); + + make_inet_addr(v->domain, v->dst_ip, DST_PORT, &addr); + ASSERT_EQ(connect(c1, &addr.sa, addr.len), 0) TH_LOG("connect(%s): %m", addr.str); + ASSERT_EQ(getsockname_port(c1), SRC_PORT); + + /* Bind to :. Block the port from reuse. */ + port_block = socket(v->domain, SOCK_STREAM, 0); + ASSERT_GE(port_block, 0) TH_LOG("socket(): %m"); + ASSERT_EQ(setsockopt(port_block, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)), 0); + + make_inet_addr(v->domain, v->bind_ip, SRC_PORT, &addr); + ASSERT_EQ(bind(port_block, &addr.sa, addr.len), 0) TH_LOG("bind(%s): %m", addr.str); + + /* Try to connect from :. Expect failure. */ + c2 = socket(v->domain, SOCK_STREAM, 0); + ASSERT_GE(c2, 0) TH_LOG("socket"); + ASSERT_EQ(setsockopt(c2, SOL_IP, IP_BIND_ADDRESS_NO_PORT, &one, sizeof(one)), 0); + + make_inet_addr(v->domain, v->src2_ip, 0, &addr); + ASSERT_EQ(bind(c2, &addr.sa, addr.len), 0) TH_LOG("bind(%s): %m", addr.str); + + make_inet_addr(v->domain, v->dst_ip, DST_PORT, &addr); + ASSERT_EQ(connect(c2, &addr.sa, addr.len), -1) TH_LOG("connect(%s)", addr.str); + ASSERT_EQ(errno, EADDRNOTAVAIL) TH_LOG("%m"); + + /* Unbind from :. Unblock the port for reuse. */ + ASSERT_EQ(close(port_block), 0); + + /* Connect again from : */ + EXPECT_EQ(connect(c2, &addr.sa, addr.len), 0) TH_LOG("connect(%s): %m", addr.str); + EXPECT_EQ(getsockname_port(c2), SRC_PORT); + + ASSERT_EQ(close(c2), 0); + ASSERT_EQ(close(c1), 0); + ASSERT_EQ(close(ln), 0); +} + +TEST_HARNESS_MAIN -- 2.43.0