Commit 9cd09482 authored by Alban Crequy's avatar Alban Crequy Committed by Andrii Nakryiko
Browse files

selftests: bpf: Add a test when bpf_probe_read_kernel_str() returns EFAULT 



This commit tests previous fix of bpf_probe_read_kernel_str().

The BPF helper bpf_probe_read_kernel_str should return -EFAULT when
given a bad source pointer and the target buffer should only be modified
to make the string NULL terminated.

bpf_probe_read_kernel_str() was previously inserting a NULL before the
beginning of the dst buffer. This test should ensure that the
implementation stays correct for now on.

Without the fix, this test will fail as follows:
  $ cd tools/testing/selftests/bpf
  $ make
  $ sudo ./test_progs --name=varlen
  ...
  test_varlen:FAIL:check got 0 != exp 66

Signed-off-by: default avatarAlban Crequy <albancrequy@linux.microsoft.com>
Signed-off-by: default avatarFrancis Laniel <flaniel@linux.microsoft.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221110085614.111213-3-albancrequy@linux.microsoft.com

Changes v1 to v2:
- add ack tag
- fix my email
- rebase on bpf tree and tag for bpf tree
parent 8678ea06

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

+7 −0
Original line number Diff line number Diff line
@@ -63,6 +63,13 @@ void test_varlen(void) 
	CHECK_VAL(data->total4, size1 + size2);

	CHECK(memcmp(data->payload4, exp_str, size1 + size2), "content_check",

	      "doesn't match!\n");



	CHECK_VAL(bss->ret_bad_read, -EFAULT);

	CHECK_VAL(data->payload_bad[0], 0x42);

	CHECK_VAL(data->payload_bad[1], 0x42);

	CHECK_VAL(data->payload_bad[2], 0);

	CHECK_VAL(data->payload_bad[3], 0x42);

	CHECK_VAL(data->payload_bad[4], 0x42);

cleanup:

	test_varlen__destroy(skel);

}

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

+5 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ __u64 payload1_len1 = 0; 
__u64 payload1_len2 = 0;

__u64 total1 = 0;

char payload1[MAX_LEN + MAX_LEN] = {};

__u64 ret_bad_read = 0;



/* .data */

int payload2_len1 = -1;
@@ -36,6 +37,8 @@ int payload4_len2 = -1; 
int total4= -1;

char payload4[MAX_LEN + MAX_LEN] = { 1 };



char payload_bad[5] = { 0x42, 0x42, 0x42, 0x42, 0x42 };



SEC("raw_tp/sys_enter")

int handler64_unsigned(void *regs)

{
@@ -61,6 +64,8 @@ int handler64_unsigned(void *regs) 


	total1 = payload - (void *)payload1;



	ret_bad_read = bpf_probe_read_kernel_str(payload_bad + 2, 1, (void *) -1);



	return 0;

}