[PATCH v2 bpf-next 2/2] selftests/bpf: Check bpf_skb_output() tracing restrictions
From: Feng Yang <hidden>
Date: 2026-09-22 01:55:48
Also in:
bpf, lkml
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [selftests] (test runners & infrastructure), kernel selftest framework, the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Shuah Khan, Shuah Khan, Linus Torvalds
From: Feng Yang <redacted> Add verifier coverage for the bpf_skb_output() tracing policy. Verify that an fentry program can still use the helper, while the equivalent fexit program is rejected at load time. Signed-off-by: Yun Lu <redacted> Signed-off-by: Feng Yang<redacted> --- .../bpf/progs/verifier_helper_restricted.c | 32 +++++++++++++++++++ 1 file changed, 32 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/verifier_helper_restricted.c b/tools/testing/selftests/bpf/progs/verifier_helper_restricted.c
index 889c9b78b912..058e71927cd5 100644
--- a/tools/testing/selftests/bpf/progs/verifier_helper_restricted.c
+++ b/tools/testing/selftests/bpf/progs/verifier_helper_restricted.c@@ -3,6 +3,7 @@ #include <linux/bpf.h> #include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> #include "bpf_misc.h" struct val {
@@ -17,6 +18,13 @@ struct { __type(value, struct val); } map_spin_lock SEC(".maps"); +struct { + __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY); + __uint(max_entries, 1); + __type(key, __u32); + __type(value, __u32); +} perf_event_map SEC(".maps"); + SEC("kprobe") __description("bpf_ktime_get_coarse_ns is forbidden in BPF_PROG_TYPE_KPROBE") __failure __msg("program of this type cannot use helper bpf_ktime_get_coarse_ns")
@@ -165,4 +173,28 @@ l0_%=: exit; \ : __clobber_all); } +SEC("fentry/skb_tx_error") +__description("bpf_skb_output is allowed in BPF_TRACE_FENTRY") +__success +int BPF_PROG(skb_output_fentry, void *skb) +{ + __u64 meta = 0; + + bpf_skb_output(skb, &perf_event_map, BPF_F_CURRENT_CPU, + &meta, sizeof(meta)); + return 0; +} + +SEC("fexit/skb_tx_error") +__description("bpf_skb_output is forbidden in BPF_TRACE_FEXIT") +__failure __msg("program of this type cannot use helper bpf_skb_output") +int BPF_PROG(skb_output_fexit, void *skb) +{ + __u64 meta = 0; + + bpf_skb_output(skb, &perf_event_map, BPF_F_CURRENT_CPU, + &meta, sizeof(meta)); + return 0; +} + char _license[] SEC("license") = "GPL";
--
2.27.0