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selftests/bpf: Fix flaky bpf_nf test when random NAT port is 0

PATCH Applied Jiayuan Chen 2 participants 2 messages Sep 4

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Kselftest BPF BPF selftests
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Jiayuan Chen

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PATCH 1/1 selftests/bpf: Fix flaky bpf_nf test when random NAT port is 0

The bpf_nf test allocs a ct, sets snat and dnat with random addr and port via bpf_ct_set_nat_info(), then looks the ct up and checks the reply tuple against what was set.

The port comes from bpf_get_prandom_u32() and can be 0. For bpf_ct_set_nat_info(), port 0 means "port not specified", so only the addr is mapped and the kernel keeps the original port. The check then compares that port with 0 and fails, which shows up as a flaky "Test for source natting" failure in CI [1][2].

Keep the random port in 1..65535 so it is always specified.

[1] https://github.com/kernel-patches/bpf/actions/runs/33830002889/job/100893868791
[2] https://github.com/kernel-patches/bpf/actions/runs/33829976794/job/100893220999

Fixes b06b45e82b59 ("selftests/bpf: add tests for bpf_ct_set_nat_info kfunc")
Signed-off-by Jiayuan Chen <[email protected]>
---
 tools/testing/selftests/bpf/progs/test_bpf_nf.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
tools/testing/selftests/bpf/progs/test_bpf_nf.c +4 -4
index df43649ecb78..eda9b7bbab75 100644
@@ -190,8 +190,8 @@ nf_ct_test(struct nf_conn *(*lookup_fn)(void *, struct bpf_sock_tuple *, u32,
 	ct = alloc_fn(ctx, &bpf_tuple, sizeof(bpf_tuple.ipv4), &opts_def,
 		      sizeof(opts_def));
 	if (ct) {
-		__u16 sport = bpf_get_prandom_u32();
-		__u16 dport = bpf_get_prandom_u32();
+		__u16 sport = bpf_get_prandom_u32() % 65535 + 1;
+		__u16 dport = bpf_get_prandom_u32() % 65535 + 1;
 		union nf_inet_addr saddr = {};
 		union nf_inet_addr daddr = {};
 		struct nf_conn *ct_ins;

@@ -293,8 +293,8 @@ nf_ct_opts_new_test(struct nf_conn *(*lookup_fn)(void *, struct bpf_sock_tuple *
 	ct = alloc_fn(ctx, &bpf_tuple, sizeof(bpf_tuple.ipv4), &opts_def,
 		      sizeof(opts_def));
 	if (ct) {
-		__u16 sport = bpf_get_prandom_u32();
-		__u16 dport = bpf_get_prandom_u32();
+		__u16 sport = bpf_get_prandom_u32() % 65535 + 1;
+		__u16 dport = bpf_get_prandom_u32() % 65535 + 1;
 		union nf_inet_addr saddr = {};
 		union nf_inet_addr daddr = {};
 		struct nf_conn *ct_ins;
Signature · 1 line
2.43.0
CI Applied
#1 lore raw
This patch was applied to bpf/bpf.git (master) by Alexei Starovoitov <[email protected]>:

Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <[email protected]>:

Quoted 11 lines · On Fri, 4 Sep 2026 15:37:39 +0800 you wrote:

The bpf_nf test allocs a ct, sets snat and dnat with random addr and port via bpf_ct_set_nat_info(), then looks the ct up and checks the reply tuple against what was set.

The port comes from bpf_get_prandom_u32() and can be 0. For bpf_ct_set_nat_info(), port 0 means "port not specified", so only the addr is mapped and the kernel keeps the original port. The check then compares that port with 0 and fails, which shows up as a flaky "Test for source natting" failure in CI [1][2].

[...]

Here is the summary with links:
- [bpf-next,v1] selftests/bpf: Fix flaky bpf_nf test when random NAT port is 0

    https://git.kernel.org/bpf/bpf/c/5e8c349bc8d7

You are awesome, thank you!

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