Commit 12e6196f authored by Yonghong Song's avatar Yonghong Song Committed by Daniel Borkmann
Browse files

selftests/bpf: Test bpf_iter buffer access with negative offset 



Commit afbf21dc ("bpf: Support readonly/readwrite buffers
in verifier") added readonly/readwrite buffer support which
is currently used by bpf_iter tracing programs. It has
a bug with incorrect parameter ordering which later fixed
by Commit f6dfbe31 ("bpf: Fix swapped arguments in calls
to check_buffer_access").

This patch added a test case with a negative offset access
which will trigger the error path.

Without Commit f6dfbe31, running the test case in the patch,
the error message looks like:
   R1_w=rdwr_buf(id=0,off=0,imm=0) R10=fp0
  ; value_sum += *(__u32 *)(value - 4);
  2: (61) r1 = *(u32 *)(r1 -4)
  R1 invalid (null) buffer access: off=-4, size=4

With the above commit, the error message looks like:
   R1_w=rdwr_buf(id=0,off=0,imm=0) R10=fp0
  ; value_sum += *(__u32 *)(value - 4);
  2: (61) r1 = *(u32 *)(r1 -4)
  R1 invalid rdwr buffer access: off=-4, size=4

Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200728221801.1090406-1-yhs@fb.com
parent 4fc00b79

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

+13 −0
Original line number Diff line number Diff line
@@ -21,6 +21,7 @@ 
#include "bpf_iter_bpf_percpu_array_map.skel.h"

#include "bpf_iter_bpf_sk_storage_map.skel.h"

#include "bpf_iter_test_kern5.skel.h"

#include "bpf_iter_test_kern6.skel.h"



static int duration;
@@ -885,6 +886,16 @@ static void test_rdonly_buf_out_of_bound(void) 
	bpf_iter_test_kern5__destroy(skel);

}



static void test_buf_neg_offset(void)

{

	struct bpf_iter_test_kern6 *skel;



	skel = bpf_iter_test_kern6__open_and_load();

	if (CHECK(skel, "bpf_iter_test_kern6__open_and_load",

		  "skeleton open_and_load unexpected success\n"))

		bpf_iter_test_kern6__destroy(skel);

}



void test_bpf_iter(void)

{

	if (test__start_subtest("btf_id_or_null"))
@@ -933,4 +944,6 @@ void test_bpf_iter(void) 
		test_bpf_sk_storage_map();

	if (test__start_subtest("rdonly-buf-out-of-bound"))

		test_rdonly_buf_out_of_bound();

	if (test__start_subtest("buf-neg-offset"))

		test_buf_neg_offset();

}

tools/testing/selftests/bpf/progs/bpf_iter_test_kern6.c

0 → 100644
+21 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2020 Facebook */

#include "bpf_iter.h"

#include <bpf/bpf_helpers.h>



char _license[] SEC("license") = "GPL";



__u32 value_sum = 0;



SEC("iter/bpf_map_elem")

int dump_bpf_hash_map(struct bpf_iter__bpf_map_elem *ctx)

{

	void *value = ctx->value;



	if (value == (void *)0)

		return 0;



	/* negative offset, verifier failure. */

	value_sum += *(__u32 *)(value - 4);

	return 0;

}