selftests/bpf: Add selftest for allow_ptr_leaks

- Without prev commit

  $ tools/testing/selftests/bpf/test_progs --name=tc_bpf
  #232/1   tc_bpf/tc_bpf_root:OK
  test_tc_bpf_non_root:PASS:set_cap_bpf_cap_net_admin 0 nsec
  test_tc_bpf_non_root:PASS:disable_cap_sys_admin 0 nsec
  0: R1=ctx(off=0,imm=0) R10=fp0
  ; if ((long)(iph + 1) > (long)skb->data_end)
  0: (61) r2 = *(u32 *)(r1 +80)         ; R1=ctx(off=0,imm=0) R2_w=pkt_end(off=0,imm=0)
  ; struct iphdr *iph = (void *)(long)skb->data + sizeof(struct ethhdr);
  1: (61) r1 = *(u32 *)(r1 +76)         ; R1_w=pkt(off=0,r=0,imm=0)
  ; if ((long)(iph + 1) > (long)skb->data_end)
  2: (07) r1 += 34                      ; R1_w=pkt(off=34,r=0,imm=0)
  3: (b4) w0 = 1                        ; R0_w=1
  4: (2d) if r1 > r2 goto pc+1
  R2 pointer comparison prohibited
  processed 5 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  test_tc_bpf_non_root:FAIL:test_tc_bpf__open_and_load unexpected error: -13
  #233/2   tc_bpf_non_root:FAIL

- With prev commit

  $ tools/testing/selftests/bpf/test_progs --name=tc_bpf
  #232/1   tc_bpf/tc_bpf_root:OK
  #232/2   tc_bpf/tc_bpf_non_root:OK
  #232     tc_bpf:OK
  Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230823020703.3790-3-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/tc_bpf.c

@@ -3,6 +3,7 @@
 #include <test_progs.h>
 #include <linux/pkt_cls.h>
 
+#include "cap_helpers.h"
 #include "test_tc_bpf.skel.h"
 
 #define LO_IFINDEX 1
@@ -327,7 +328,7 @@ static int test_tc_bpf_api(struct bpf_tc_hook *hook, int fd)
 	return 0;
 }
 
-void test_tc_bpf(void)
+void tc_bpf_root(void)
 {
 	DECLARE_LIBBPF_OPTS(bpf_tc_hook, hook, .ifindex = LO_IFINDEX,
 			    .attach_point = BPF_TC_INGRESS);
@@ -393,3 +394,36 @@ void test_tc_bpf(void)
 	}
 	test_tc_bpf__destroy(skel);
 }
+
+void tc_bpf_non_root(void)
+{
+	struct test_tc_bpf *skel = NULL;
+	__u64 caps = 0;
+	int ret;
+
+	/* In case CAP_BPF and CAP_PERFMON is not set */
+	ret = cap_enable_effective(1ULL << CAP_BPF | 1ULL << CAP_NET_ADMIN, &caps);
+	if (!ASSERT_OK(ret, "set_cap_bpf_cap_net_admin"))
+		return;
+	ret = cap_disable_effective(1ULL << CAP_SYS_ADMIN | 1ULL << CAP_PERFMON, NULL);
+	if (!ASSERT_OK(ret, "disable_cap_sys_admin"))
+		goto restore_cap;
+
+	skel = test_tc_bpf__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_tc_bpf__open_and_load"))
+		goto restore_cap;
+
+	test_tc_bpf__destroy(skel);
+
+restore_cap:
+	if (caps)
+		cap_enable_effective(caps, NULL);
+}
+
+void test_tc_bpf(void)
+{
+	if (test__start_subtest("tc_bpf_root"))
+		tc_bpf_root();
+	if (test__start_subtest("tc_bpf_non_root"))
+		tc_bpf_non_root();
+}

tools/testing/selftests/bpf/progs/test_tc_bpf.c

@@ -2,6 +2,8 @@
 
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
+#include <linux/if_ether.h>
+#include <linux/ip.h>
 
 /* Dummy prog to test TC-BPF API */
 
@@ -10,3 +12,14 @@ int cls(struct __sk_buff *skb)
 {
 	return 0;
 }
+
+/* Prog to verify tc-bpf without cap_sys_admin and cap_perfmon */
+SEC("tcx/ingress")
+int pkt_ptr(struct __sk_buff *skb)
+{
+	struct iphdr *iph = (void *)(long)skb->data + sizeof(struct ethhdr);
+
+	if ((long)(iph + 1) > (long)skb->data_end)
+		return 1;
+	return 0;
+}