Subject: [PATCH bpf-next v2 2/2] selftests/bpf: test references to nf_conn

From: Matthew Cover <[email-masked]>
Date: Tue, 21 Jan 2020 13:22:33 -0700

Make sure that returning a struct nf_conn * reference invokes
the reference tracking machinery in the verifier.

Signed-off-by: Matthew Cover <[email-masked]>
---
 tools/testing/selftests/bpf/test_verifier.c        | 18 ++++++++
 .../testing/selftests/bpf/verifier/ref_tracking.c  | 48 ++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 87eaa49..7569db2 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -294,6 +294,24 @@ static void bpf_fill_scale(struct bpf_test *self)
 	}
 }
 
+/* BPF_CT_LOOKUP contains 13 instructions, if you need to fix up maps */
+#define BPF_CT_LOOKUP(func)						\
+	/* struct bpf_nf_conntrack_tuple tuple = {} */			\
+	BPF_MOV64_IMM(BPF_REG_2, 0),					\
+	BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_2, -8),			\
+	BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_2, -16),		\
+	BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_2, -24),		\
+	BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_2, -32),		\
+	BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_2, -40),		\
+	BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_2, -48),		\
+	/* ct = func(ctx, &tuple, sizeof tuple, 0, 0) */		\
+	BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),				\
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -48),				\
+	BPF_MOV64_IMM(BPF_REG_3, sizeof(struct bpf_nf_conntrack_tuple)),\
+	BPF_MOV64_IMM(BPF_REG_4, 0),					\
+	BPF_MOV64_IMM(BPF_REG_5, 0),					\
+	BPF_EMIT_CALL(BPF_FUNC_ ## func)
+
 /* BPF_SK_LOOKUP contains 13 instructions, if you need to fix up maps */
 #define BPF_SK_LOOKUP(func)						\
 	/* struct bpf_sock_tuple tuple = {} */				\
diff --git a/tools/testing/selftests/bpf/verifier/ref_tracking.c b/tools/testing/selftests/bpf/verifier/ref_tracking.c
index 604b461..de5c550a 100644
--- a/tools/testing/selftests/bpf/verifier/ref_tracking.c
+++ b/tools/testing/selftests/bpf/verifier/ref_tracking.c
@@ -21,6 +21,17 @@
 	.result = REJECT,
 },
 {
+	"reference tracking: leak potential reference to nf_conn",
+	.insns = {
+	BPF_CT_LOOKUP(ct_lookup_tcp),
+	BPF_MOV64_REG(BPF_REG_6, BPF_REG_0), /* leak reference */
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.errstr = "Unreleased reference",
+	.result = REJECT,
+},
+{
 	"reference tracking: leak potential reference on stack",
 	.insns = {
 	BPF_SK_LOOKUP(sk_lookup_tcp),
@@ -72,6 +83,17 @@
 	.result = REJECT,
 },
 {
+	"reference tracking: zero potential reference to nf_conn",
+	.insns = {
+	BPF_CT_LOOKUP(ct_lookup_tcp),
+	BPF_MOV64_IMM(BPF_REG_0, 0), /* leak reference */
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.errstr = "Unreleased reference",
+	.result = REJECT,
+},
+{
 	"reference tracking: copy and zero potential references",
 	.insns = {
 	BPF_SK_LOOKUP(sk_lookup_tcp),
@@ -113,6 +135,20 @@
 	.result = REJECT,
 },
 {
+	"reference tracking: release reference to nf_conn without check",
+	.insns = {
+	BPF_CT_LOOKUP(ct_lookup_tcp),
+	/* reference in r0 may be NULL */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_MOV64_IMM(BPF_REG_2, 0),
+	BPF_EMIT_CALL(BPF_FUNC_ct_release),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.errstr = "type=nf_conn_or_null expected=nf_conn",
+	.result = REJECT,
+},
+{
 	"reference tracking: release reference",
 	.insns = {
 	BPF_SK_LOOKUP(sk_lookup_tcp),
@@ -137,6 +173,18 @@
 	.result = ACCEPT,
 },
 {
+	"reference tracking: release reference to nf_conn",
+	.insns = {
+	BPF_CT_LOOKUP(ct_lookup_tcp),
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
+	BPF_EMIT_CALL(BPF_FUNC_ct_release),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.result = ACCEPT,
+},
+{
 	"reference tracking: release reference 2",
 	.insns = {
 	BPF_SK_LOOKUP(sk_lookup_tcp),
-- 
1.8.3.1