[PATCH 5.6 165/166] bpf: Test_progs, add test to catch retval refine error handling

From: Greg Kroah-Hartman
Date: Wed Apr 22 2020 - 06:28:04 EST


From: John Fastabend <john.fastabend@xxxxxxxxx>

commit d2db08c7a14e0b5eed6132baf258b80622e041a9 upstream.

Before this series the verifier would clamp return bounds of
bpf_get_stack() to [0, X] and this led the verifier to believe
that a JMP_JSLT 0 would be false and so would prune that path.

The result is anything hidden behind that JSLT would be unverified.
Add a test to catch this case by hiding an goto pc-1 behind the
check which will cause an infinite loop if not rejected.

Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/158560423908.10843.11783152347709008373.stgit@john-Precision-5820-Tower
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c | 5 ++
tools/testing/selftests/bpf/progs/test_get_stack_rawtp_err.c | 26 +++++++++++
2 files changed, 31 insertions(+)

--- a/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
+++ b/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
@@ -82,6 +82,7 @@ static void get_stack_print_output(void
void test_get_stack_raw_tp(void)
{
const char *file = "./test_get_stack_rawtp.o";
+ const char *file_err = "./test_get_stack_rawtp_err.o";
const char *prog_name = "raw_tracepoint/sys_enter";
int i, err, prog_fd, exp_cnt = MAX_CNT_RAWTP;
struct perf_buffer_opts pb_opts = {};
@@ -93,6 +94,10 @@ void test_get_stack_raw_tp(void)
struct bpf_map *map;
cpu_set_t cpu_set;

+ err = bpf_prog_load(file_err, BPF_PROG_TYPE_RAW_TRACEPOINT, &obj, &prog_fd);
+ if (CHECK(err >= 0, "prog_load raw tp", "err %d errno %d\n", err, errno))
+ return;
+
err = bpf_prog_load(file, BPF_PROG_TYPE_RAW_TRACEPOINT, &obj, &prog_fd);
if (CHECK(err, "prog_load raw tp", "err %d errno %d\n", err, errno))
return;
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_get_stack_rawtp_err.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+#define MAX_STACK_RAWTP 10
+
+SEC("raw_tracepoint/sys_enter")
+int bpf_prog2(void *ctx)
+{
+ __u64 stack[MAX_STACK_RAWTP];
+ int error;
+
+ /* set all the flags which should return -EINVAL */
+ error = bpf_get_stack(ctx, stack, 0, -1);
+ if (error < 0)
+ goto loop;
+
+ return error;
+loop:
+ while (1) {
+ error++;
+ }
+}
+
+char _license[] SEC("license") = "GPL";