From nobody Thu Apr 2 09:20:29 2026 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FF1C3ACEEF for ; Mon, 30 Mar 2026 08:08:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774858095; cv=none; b=MKzu/s83dekFXOdDXow1VsWPgbXVCa7Tv/5etQlm6S5Yh/NG7zb/fVekBMAI2I3tfH9mndTE/COGJ0YRacEgHTq96qFZY3Urylu7/oG8niEWQacWhnEu/QdB9DkqYuY91VHE/4Mie4w9NL1Hu22iRvufe4b0X8HZ2BpdUBe8TeU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774858095; c=relaxed/simple; bh=38jvFkpVvultNQ5a1ueAN2rm02/oqIbCKLjCvkvytuM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=H7e4acn4vT4u6brn2VmbMzkMknRITd77sz84N3EItY6DqImYZaiS8qm7xvM4JYscjSsCVZ4VFhglZNp6iXNFGwsKMIIHN2oDzz7A5qFeTfSAmYLRDP4Y+Qa6JRAAnIBE+qRgFOpgpXKXT7lc5mO6/aRmIFOJckJDdGaViL2aPQ4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=PfswceL2; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="PfswceL2" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774858091; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=b2pQUSQjr2/6ekAGkm9DFB/39oP/oelgKsn7Un+VkTE=; b=PfswceL2+VoG2lQh2U3k0JpPdTruTiTwsz/vXX/ghTvquJV1dEetoY4QyzArqjMvFQpAx8 XvIIOAYkgYH1ITb/qk+ndjFTOqqy7grKkoAiFrkpZAyFO+zEylHorkemAtH8njvuxTjc49 LQXR+AgjmRCc5YoOjXQnOpwO+RvUWto= From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Kuniyuki Iwashima , Martin KaFai Lau , Daniel Borkmann , John Fastabend , Stanislav Fomichev , Alexei Starovoitov , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf v4 1/2] bpf: tcp: Reject non-TCP skb in bpf_sk_assign_tcp_reqsk() Date: Mon, 30 Mar 2026 16:07:25 +0800 Message-ID: <20260330080746.319680-2-jiayuan.chen@linux.dev> In-Reply-To: <20260330080746.319680-1-jiayuan.chen@linux.dev> References: <20260330080746.319680-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" bpf_sk_assign_tcp_reqsk() only validates skb->protocol (L3) but does not check the L4 protocol in the IP header. A BPF program can call this kfunc on a UDP skb with a valid TCP listener socket, which will succeed and attach a TCP reqsk to the UDP skb. When the UDP skb enters the UDP receive path, skb_steal_sock() returns the TCP listener from the reqsk. The UDP code then passes this TCP socket to udp_unicast_rcv_skb() -> __udp_enqueue_schedule_skb(), which casts it to udp_sock and accesses UDP-specific fields at invalid offsets, causing a null pointer dereference and kernel panic: BUG: KASAN: null-ptr-deref in __udp_enqueue_schedule_skb+0x19d/0x1df0 Read of size 4 at addr 0000000000000008 by task test_progs/537 CPU: 1 UID: 0 PID: 537 Comm: test_progs Not tainted 7.0.0-rc4+ #46 PREEMPT Call Trace: dump_stack_lvl (lib/dump_stack.c:123) print_report (mm/kasan/report.c:487) kasan_report (mm/kasan/report.c:597) __kasan_check_read (mm/kasan/shadow.c:32) __udp_enqueue_schedule_skb (net/ipv4/udp.c:1719) udp_queue_rcv_one_skb (net/ipv4/udp.c:2370 net/ipv4/udp.c:2500) udp_queue_rcv_skb (net/ipv4/udp.c:2532) udp_unicast_rcv_skb (net/ipv4/udp.c:2684) __udp4_lib_rcv (net/ipv4/udp.c:2742) udp_rcv (net/ipv4/udp.c:2937) ip_protocol_deliver_rcu (net/ipv4/ip_input.c:209) ip_local_deliver_finish (./include/linux/rcupdate.h:879 net/ipv4/ip_inpu= t.c:242) ip_local_deliver (net/ipv4/ip_input.c:265) __netif_receive_skb_one_core (net/core/dev.c:6164 (discriminator 4)) __netif_receive_skb (net/core/dev.c:6280) Fix this by checking the IP header's protocol field in bpf_sk_assign_tcp_reqsk() and rejecting non-TCP skbs with -EINVAL. Fixes: e472f88891ab ("bpf: tcp: Support arbitrary SYN Cookie.") Reviewed-by: Kuniyuki Iwashima Signed-off-by: Jiayuan Chen --- net/core/filter.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index 78b548158fb0..fb975bcce804 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -12248,11 +12248,17 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __= sk_buff *s, struct sock *sk, =20 switch (skb->protocol) { case htons(ETH_P_IP): + if (ip_hdr(skb)->protocol !=3D IPPROTO_TCP) + return -EINVAL; + ops =3D &tcp_request_sock_ops; min_mss =3D 536; break; #if IS_BUILTIN(CONFIG_IPV6) case htons(ETH_P_IPV6): + if (ipv6_hdr(skb)->nexthdr !=3D IPPROTO_TCP) + return -EINVAL; + ops =3D &tcp6_request_sock_ops; min_mss =3D IPV6_MIN_MTU - 60; break; --=20 2.43.0 From nobody Thu Apr 2 09:20:29 2026 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DDAE63A874F for ; Mon, 30 Mar 2026 08:08:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774858107; cv=none; b=ieR+7U2PwchKSJu4uhXFtTazOfgIsuceiIllhZDs6YJFygzT7Of7jstTd6waZuyjmpvOvBeXgqwXrl+5BTkyAoFhHpTuK5bbyjgYYi4BOzpUYpJniDLbepwLKw9JypK47QGHHUXlczT0e1u6MU2zH2sWL9cfU7n+IxRvxtOq9EY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774858107; c=relaxed/simple; bh=iEUY+9gWrFjCtPRfzgVXMQXVeRXlkW/T9DnKRXBgG1s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kZAPHTUUnSO7z4hjYMPEKDxL7wQ7YfY0NrvOjy7eDcLGWY2ZEelKqdWXYUk8CHJSDJVLg2e7GQnxofwO3YQTDd3dP/p+krL4/A0LSZSgt03I13wORtzpYXJKyaNtD9/GfY77nWkJMBQQmjfjbT9kwGG72L7a2LZSfPimmuhQALc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=pHIGHnzI; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="pHIGHnzI" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774858104; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PLKWQBCloH5Wb28Pxxsg/3g0WCGImQfPe+MsKG52h4o=; b=pHIGHnzIOmsHdlZR/KXb+xmiMdZXmItx2ZO14m6BTEr3f1PIZacMfJf4y1xA0YC7LXvOlo lakclR+tdDz+s5ZBe0jmybb8LipZlv5yPL7awoAOxwxHtbYNOEpRETKw9chn6l0XcyKqQK JCBAFsEM3l1MHnQgheTMZLSLZ3HXgWo= From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , Kuniyuki Iwashima , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf v4 2/2] selftests/bpf: Add protocol check test for bpf_sk_assign_tcp_reqsk() Date: Mon, 30 Mar 2026 16:07:26 +0800 Message-ID: <20260330080746.319680-3-jiayuan.chen@linux.dev> In-Reply-To: <20260330080746.319680-1-jiayuan.chen@linux.dev> References: <20260330080746.319680-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Add test_tcp_custom_syncookie_protocol_check to verify that bpf_sk_assign_tcp_reqsk() rejects non-TCP skbs. The test sends a UDP packet through TC ingress where a BPF program calls bpf_sk_assign_tcp_reqsk() on it and checks that the kfunc returns an error. A UDP server recv() is used as synchronization to ensure the BPF program has finished processing before checking the result. Without the fix in bpf_sk_assign_tcp_reqsk(), the kfunc succeeds and attaches a TCP reqsk to the UDP skb, which causes a null pointer dereference panic when the kernel processes it through the UDP receive path. Test result: ./test_progs -a tcp_custom_syncookie_protocol_check -v setup_netns:PASS:create netns 0 nsec setup_netns:PASS:ip 0 nsec write_sysctl:PASS:open sysctl 0 nsec write_sysctl:PASS:write sysctl 0 nsec setup_netns:PASS:write_sysctl 0 nsec test_tcp_custom_syncookie_protocol_check:PASS:open_and_load 0 nsec setup_tc:PASS:qdisc add dev lo clsact 0 nsec setup_tc:PASS:filter add dev lo ingress 0 nsec run_protocol_check:PASS:start tcp_server 0 nsec run_protocol_check:PASS:start udp_server 0 nsec run_protocol_check:PASS:connect udp_client 0 nsec run_protocol_check:PASS:send udp 0 nsec run_protocol_check:PASS:recv udp 0 nsec run_protocol_check:PASS:udp_intercepted 0 nsec run_protocol_check:PASS:assign_ret 0 nsec #471/1 tcp_custom_syncookie_protocol_check/IPv4 TCP:OK run_protocol_check:PASS:start tcp_server 0 nsec run_protocol_check:PASS:start udp_server 0 nsec run_protocol_check:PASS:connect udp_client 0 nsec run_protocol_check:PASS:send udp 0 nsec run_protocol_check:PASS:recv udp 0 nsec run_protocol_check:PASS:udp_intercepted 0 nsec run_protocol_check:PASS:assign_ret 0 nsec #471/2 tcp_custom_syncookie_protocol_check/IPv6 TCP:OK #471 tcp_custom_syncookie_protocol_check:OK Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED Signed-off-by: Jiayuan Chen --- .../bpf/prog_tests/tcp_custom_syncookie.c | 91 ++++++++++++++- .../bpf/progs/test_tcp_custom_syncookie.c | 109 ++++++++++++++++++ 2 files changed, 196 insertions(+), 4 deletions(-) diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c = b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c index eaf441dc7e79..6e29402c4c59 100644 --- a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c +++ b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c @@ -5,6 +5,7 @@ #include #include #include +#include =20 #include "test_progs.h" #include "cgroup_helpers.h" @@ -47,11 +48,10 @@ static int setup_netns(void) return -1; } =20 -static int setup_tc(struct test_tcp_custom_syncookie *skel) +static int setup_tc(int prog_fd) { LIBBPF_OPTS(bpf_tc_hook, qdisc_lo, .attach_point =3D BPF_TC_INGRESS); - LIBBPF_OPTS(bpf_tc_opts, tc_attach, - .prog_fd =3D bpf_program__fd(skel->progs.tcp_custom_syncookie)); + LIBBPF_OPTS(bpf_tc_opts, tc_attach, .prog_fd =3D prog_fd); =20 qdisc_lo.ifindex =3D if_nametoindex("lo"); if (!ASSERT_OK(bpf_tc_hook_create(&qdisc_lo), "qdisc add dev lo clsact")) @@ -127,7 +127,7 @@ void test_tcp_custom_syncookie(void) if (!ASSERT_OK_PTR(skel, "open_and_load")) return; =20 - if (setup_tc(skel)) + if (setup_tc(bpf_program__fd(skel->progs.tcp_custom_syncookie))) goto destroy_skel; =20 for (i =3D 0; i < ARRAY_SIZE(test_cases); i++) { @@ -145,6 +145,89 @@ void test_tcp_custom_syncookie(void) =20 destroy_skel: system("tc qdisc del dev lo clsact"); + test_tcp_custom_syncookie__destroy(skel); +} + +/* Test: bpf_sk_assign_tcp_reqsk() should reject non-TCP skb. + * + * Send a UDP packet through TC ingress where a BPF program calls + * bpf_sk_assign_tcp_reqsk() on it. The kfunc should return an error + * because the skb carries UDP, not TCP. + * + * TCP and UDP servers share the same port. The BPF program intercepts + * the UDP packet, looks up the TCP listener via the dest port, and + * attempts to assign a TCP reqsk to the UDP skb. + */ +static void run_protocol_check(struct test_tcp_custom_syncookie *skel, + int family, const char *addr) +{ + int tcp_server =3D -1, udp_server =3D -1, udp_client =3D -1; + char buf[32] =3D "test"; + int port, ret; + + tcp_server =3D start_server(family, SOCK_STREAM, addr, 0, 0); + if (!ASSERT_NEQ(tcp_server, -1, "start tcp_server")) + return; + + port =3D ntohs(get_socket_local_port(tcp_server)); + + /* UDP server on same port for synchronization and port sharing */ + udp_server =3D start_server(family, SOCK_DGRAM, addr, port, 0); + if (!ASSERT_NEQ(udp_server, -1, "start udp_server")) + goto close_tcp; + + skel->bss->udp_intercepted =3D false; + skel->bss->assign_ret =3D 0; + + udp_client =3D connect_to_fd(udp_server, 0); + if (!ASSERT_NEQ(udp_client, -1, "connect udp_client")) + goto close_udp_server; =20 + ret =3D send(udp_client, buf, sizeof(buf), 0); + if (!ASSERT_EQ(ret, sizeof(buf), "send udp")) + goto close_udp_client; + + /* recv() ensures TC ingress BPF has processed the skb */ + ret =3D recv(udp_server, buf, sizeof(buf), 0); + if (!ASSERT_EQ(ret, sizeof(buf), "recv udp")) + goto close_udp_client; + + ASSERT_EQ(skel->bss->udp_intercepted, true, "udp_intercepted"); + + ASSERT_EQ(skel->bss->assign_ret, -EINVAL, "assign_ret"); + +close_udp_client: + close(udp_client); +close_udp_server: + close(udp_server); +close_tcp: + close(tcp_server); +} + +void test_tcp_custom_syncookie_protocol_check(void) +{ + struct test_tcp_custom_syncookie *skel; + int i; + + if (setup_netns()) + return; + + skel =3D test_tcp_custom_syncookie__open_and_load(); + if (!ASSERT_OK_PTR(skel, "open_and_load")) + return; + + if (setup_tc(bpf_program__fd(skel->progs.tcp_custom_syncookie_badproto))) + goto destroy_skel; + + for (i =3D 0; i < ARRAY_SIZE(test_cases); i++) { + if (!test__start_subtest(test_cases[i].name)) + continue; + + run_protocol_check(skel, test_cases[i].family, + test_cases[i].addr); + } + +destroy_skel: + system("tc qdisc del dev lo clsact"); test_tcp_custom_syncookie__destroy(skel); } diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c = b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c index 7d5293de1952..bd3fad3dd503 100644 --- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c +++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c @@ -588,4 +588,113 @@ int tcp_custom_syncookie(struct __sk_buff *skb) return tcp_handle_ack(&ctx); } =20 +/* Test: call bpf_sk_assign_tcp_reqsk() on a UDP skb. + * The kfunc should reject it because the skb is not TCP. + * + * TCP and UDP servers share the same port. The BPF program intercepts + * UDP packets, looks up the TCP listener on the same port, and tries + * to assign a TCP reqsk to the UDP skb. + */ +int assign_ret =3D 0; +bool udp_intercepted =3D false; + +static int badproto_lookup_assign(struct __sk_buff *skb, struct udphdr *ud= p, + struct bpf_sock_tuple *tuple, u32 tuple_size) +{ + struct bpf_tcp_req_attrs attrs =3D {}; + struct bpf_sock *skc; + struct sock *sk; + + skc =3D bpf_skc_lookup_tcp(skb, tuple, tuple_size, -1, 0); + if (!skc) + return TC_ACT_OK; + + if (skc->state !=3D TCP_LISTEN) { + bpf_sk_release(skc); + return TC_ACT_OK; + } + + sk =3D (struct sock *)bpf_skc_to_tcp_sock(skc); + if (!sk) { + bpf_sk_release(skc); + return TC_ACT_OK; + } + + attrs.mss =3D 1460; + attrs.wscale_ok =3D 1; + attrs.snd_wscale =3D 7; + attrs.rcv_wscale =3D 7; + attrs.sack_ok =3D 1; + + assign_ret =3D bpf_sk_assign_tcp_reqsk(skb, sk, &attrs, sizeof(attrs)); + + bpf_sk_release(skc); + return TC_ACT_OK; +} + +SEC("tc") +int tcp_custom_syncookie_badproto(struct __sk_buff *skb) +{ + void *data =3D (void *)(long)skb->data; + void *data_end =3D (void *)(long)skb->data_end; + struct bpf_sock_tuple tuple =3D {}; + struct ethhdr *eth; + struct iphdr *iph; + struct ipv6hdr *ip6h; + struct udphdr *udp; + + eth =3D (struct ethhdr *)data; + if (eth + 1 > data_end) + return TC_ACT_OK; + + switch (bpf_ntohs(eth->h_proto)) { + case ETH_P_IP: + iph =3D (struct iphdr *)(eth + 1); + if (iph + 1 > data_end) + return TC_ACT_OK; + + if (iph->protocol !=3D IPPROTO_UDP) + return TC_ACT_OK; + + udp =3D (struct udphdr *)(iph + 1); + if (udp + 1 > data_end) + return TC_ACT_OK; + + udp_intercepted =3D true; + + tuple.ipv4.saddr =3D iph->saddr; + tuple.ipv4.daddr =3D iph->daddr; + tuple.ipv4.sport =3D udp->source; + tuple.ipv4.dport =3D udp->dest; + + return badproto_lookup_assign(skb, udp, &tuple, + sizeof(tuple.ipv4)); + case ETH_P_IPV6: + ip6h =3D (struct ipv6hdr *)(eth + 1); + if (ip6h + 1 > data_end) + return TC_ACT_OK; + + if (ip6h->nexthdr !=3D IPPROTO_UDP) + return TC_ACT_OK; + + udp =3D (struct udphdr *)(ip6h + 1); + if (udp + 1 > data_end) + return TC_ACT_OK; + + udp_intercepted =3D true; + + __builtin_memcpy(tuple.ipv6.saddr, &ip6h->saddr, + sizeof(tuple.ipv6.saddr)); + __builtin_memcpy(tuple.ipv6.daddr, &ip6h->daddr, + sizeof(tuple.ipv6.daddr)); + tuple.ipv6.sport =3D udp->source; + tuple.ipv6.dport =3D udp->dest; + + return badproto_lookup_assign(skb, udp, &tuple, + sizeof(tuple.ipv6)); + default: + return TC_ACT_OK; + } +} + char _license[] SEC("license") =3D "GPL"; --=20 2.43.0