Verify that bpf_skb_adjust_room() clears the routing dst even when the encap L3 protocol matches the original packet (e.g. IPIP). The dst selected for the inner packet is not valid for the encapsulated result; a stale dst could lead to misrouting.
Signed-off-by: Jakub Kicinski <[email protected]> --- CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] CC: [email protected] --- .../selftests/bpf/prog_tests/test_dst_clear.c | 75 +++++++++++++++++++ .../selftests/bpf/progs/test_dst_clear.c | 57 ++++++++++++++ 2 files changed, 132 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/test_dst_clear.c create mode 100644 tools/testing/selftests/bpf/progs/test_dst_clear.c diff --git a/tools/testing/selftests/bpf/prog_tests/test_dst_clear.c b/tools/testing/selftests/bpf/prog_tests/test_dst_clear.c new file mode 100644 index 000000000000..8190c56556fb --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/test_dst_clear.c @@ -0,0 +1,75 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ + +#include <sys/types.h> +#include <sys/socket.h> +#include <net/if.h> + +#include "test_progs.h" +#include "network_helpers.h" +#include "test_dst_clear.skel.h" + +#define NS_TEST "dst_clear_ns" +#define IPV4_IFACE_ADDR "1.0.0.1" +#define UDP_TEST_PORT 7777 + +void test_dst_clear(void) +{ + LIBBPF_OPTS(bpf_tc_hook, qdisc_hook, .attach_point = BPF_TC_EGRESS); + LIBBPF_OPTS(bpf_tc_opts, tc_attach); + struct nstoken *nstoken = NULL; + struct test_dst_clear *skel; + struct sockaddr_in addr; + socklen_t addrlen; + char buf[128] = {}; + int sockfd, err; + + skel = test_dst_clear__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel open_and_load")) + return; + + SYS(fail, "ip netns add %s", NS_TEST); + SYS(fail, "ip -net %s addr add %s/8 dev lo", NS_TEST, IPV4_IFACE_ADDR); + SYS(fail, "ip -net %s link set dev lo up", NS_TEST); + + nstoken = open_netns(NS_TEST); + if (!ASSERT_OK_PTR(nstoken, "open_netns")) + goto fail; + + qdisc_hook.ifindex = if_nametoindex("lo"); + if (!ASSERT_GT(qdisc_hook.ifindex, 0, "if_nametoindex lo")) + goto fail; + + err = bpf_tc_hook_create(&qdisc_hook); + if (!ASSERT_OK(err, "create qdisc hook")) + goto fail; + + tc_attach.prog_fd = bpf_program__fd(skel->progs.dst_clear); + err = bpf_tc_attach(&qdisc_hook, &tc_attach); + if (!ASSERT_OK(err, "attach filter")) + goto fail; + + addrlen = sizeof(addr); + err = make_sockaddr(AF_INET, IPV4_IFACE_ADDR, UDP_TEST_PORT, + (void *)&addr, &addrlen); + if (!ASSERT_OK(err, "make_sockaddr")) + goto fail; + sockfd = socket(AF_INET, SOCK_DGRAM, 0); + if (!ASSERT_NEQ(sockfd, -1, "socket")) + goto fail; + err = sendto(sockfd, buf, sizeof(buf), 0, (void *)&addr, addrlen); + close(sockfd); + if (!ASSERT_EQ(err, sizeof(buf), "send")) + goto fail; + + ASSERT_TRUE(skel->bss->had_dst, "had_dst"); + ASSERT_TRUE(skel->bss->dst_cleared, "dst_cleared"); + +fail: + if (nstoken) { + bpf_tc_hook_destroy(&qdisc_hook); + close_netns(nstoken); + } + SYS_NOFAIL("ip netns del " NS_TEST); + test_dst_clear__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/test_dst_clear.c b/tools/testing/selftests/bpf/progs/test_dst_clear.c new file mode 100644 index 000000000000..7ac9604fd99c --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_dst_clear.c @@ -0,0 +1,57 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ + +#include "vmlinux.h" +#include "bpf_tracing_net.h" +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_endian.h> + +#define UDP_TEST_PORT 7777 + +void *bpf_cast_to_kern_ctx(void *) __ksym; + +bool had_dst = false; +bool dst_cleared = false; + +SEC("tc") +int dst_clear(struct __sk_buff *skb) +{ + struct sk_buff *kskb; + struct iphdr iph; + struct udphdr udph; + int err; + + if (skb->protocol != __bpf_constant_htons(ETH_P_IP)) + return TC_ACT_OK; + + if (bpf_skb_load_bytes(skb, ETH_HLEN, &iph, sizeof(iph))) + return TC_ACT_OK; + + if (iph.protocol != IPPROTO_UDP) + return TC_ACT_OK; + + if (bpf_skb_load_bytes(skb, ETH_HLEN + sizeof(iph), &udph, sizeof(udph))) + return TC_ACT_OK; + + if (udph.dest != __bpf_constant_htons(UDP_TEST_PORT)) + return TC_ACT_OK; + + kskb = bpf_cast_to_kern_ctx(skb); + had_dst = (kskb->_skb_refdst != 0); + + /* Same-protocol encap (IPIP): protocol stays IPv4, but the dst + * from the original routing is no longer valid for the outer hdr. + */ + err = bpf_skb_adjust_room(skb, (s32)sizeof(struct iphdr), + BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_FIXED_GSO | + BPF_F_ADJ_ROOM_ENCAP_L3_IPV4); + if (err) + return TC_ACT_SHOT; + + dst_cleared = (kskb->_skb_refdst == 0); + + return TC_ACT_SHOT; +} + +char __license[] SEC("license") = "GPL"; -- 2.53.0
