* [PATCH bpf-next] selftests/bpf: Fix dynptr/test_probe_read_user_str_dynptr test failure
@ 2025-05-15 19:51 Yonghong Song
2025-05-16 16:03 ` Mykyta Yatsenko
0 siblings, 1 reply; 3+ messages in thread
From: Yonghong Song @ 2025-05-15 19:51 UTC (permalink / raw)
To: bpf
Cc: Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann, kernel-team,
Martin KaFai Lau, Mykyta Yatsenko
When running bpf selftests with llvm18 compiler, I hit the following
test failure:
verify_success:PASS:dynptr_success__open 0 nsec
verify_success:PASS:bpf_object__find_program_by_name 0 nsec
verify_success:PASS:dynptr_success__load 0 nsec
verify_success:PASS:test_run 0 nsec
verify_success:FAIL:err unexpected err: actual 1 != expected 0
#91/19 dynptr/test_probe_read_user_str_dynptr:FAIL
#91 dynptr:FAIL
I did some analysis and found that the test failure is related to
lib/strncpy_from_user.c function do_strncpy_from_user():
...
byte_at_a_time:
while (max) {
char c;
unsafe_get_user(c,src+res, efault);
dst[res] = c;
if (!c)
return res;
res++;
max--;
}
...
Depending on whether the character 'c' is '\0' or not, the
return value 'res' could be different.
In prog_tests/dynptr.c, we have
char user_data[384] = {[0 ... 382] = 'a', '\0'};
the user_data[383] is '\0'. This will cause the following
error in progs/dynptr_success.c:
test_dynptr_probe_str_xdp:
...
bpf_for(i, 0, ARRAY_SIZE(test_len)) {
__u32 len = test_len[i];
cnt = bpf_read_dynptr_fn(&ptr_xdp, off, len, ptr);
if (cnt != len)
err = 1; <=== error happens here
...
In the above particular case, len is 384 and cnt is 383.
If user_data[384] is changed to
char user_data[384] = {[0 ... 383] = 'a'};
The above error will not happen and the test will run successfully.
Cc: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
tools/testing/selftests/bpf/prog_tests/dynptr.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c b/tools/testing/selftests/bpf/prog_tests/dynptr.c
index 62e7ec775f24..4cc61afa63b4 100644
--- a/tools/testing/selftests/bpf/prog_tests/dynptr.c
+++ b/tools/testing/selftests/bpf/prog_tests/dynptr.c
@@ -45,7 +45,7 @@ static struct {
static void verify_success(const char *prog_name, enum test_setup_type setup_type)
{
- char user_data[384] = {[0 ... 382] = 'a', '\0'};
+ char user_data[384] = {[0 ... 383] = 'a'};
struct dynptr_success *skel;
struct bpf_program *prog;
struct bpf_link *link;
--
2.47.1
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH bpf-next] selftests/bpf: Fix dynptr/test_probe_read_user_str_dynptr test failure
2025-05-15 19:51 [PATCH bpf-next] selftests/bpf: Fix dynptr/test_probe_read_user_str_dynptr test failure Yonghong Song
@ 2025-05-16 16:03 ` Mykyta Yatsenko
2025-05-16 16:23 ` Yonghong Song
0 siblings, 1 reply; 3+ messages in thread
From: Mykyta Yatsenko @ 2025-05-16 16:03 UTC (permalink / raw)
To: Yonghong Song, bpf
Cc: Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann, kernel-team,
Martin KaFai Lau, Mykyta Yatsenko
On 5/15/25 20:51, Yonghong Song wrote:
> When running bpf selftests with llvm18 compiler, I hit the following
> test failure:
>
> verify_success:PASS:dynptr_success__open 0 nsec
> verify_success:PASS:bpf_object__find_program_by_name 0 nsec
> verify_success:PASS:dynptr_success__load 0 nsec
> verify_success:PASS:test_run 0 nsec
> verify_success:FAIL:err unexpected err: actual 1 != expected 0
> #91/19 dynptr/test_probe_read_user_str_dynptr:FAIL
> #91 dynptr:FAIL
>
> I did some analysis and found that the test failure is related to
> lib/strncpy_from_user.c function do_strncpy_from_user():
>
> ...
> byte_at_a_time:
> while (max) {
> char c;
>
> unsafe_get_user(c,src+res, efault);
> dst[res] = c;
> if (!c)
> return res;
> res++;
> max--;
> }
> ...
>
> Depending on whether the character 'c' is '\0' or not, the
> return value 'res' could be different.
>
> In prog_tests/dynptr.c, we have
> char user_data[384] = {[0 ... 382] = 'a', '\0'};
> the user_data[383] is '\0'. This will cause the following
> error in progs/dynptr_success.c:
>
> test_dynptr_probe_str_xdp:
> ...
> bpf_for(i, 0, ARRAY_SIZE(test_len)) {
> __u32 len = test_len[i];
>
> cnt = bpf_read_dynptr_fn(&ptr_xdp, off, len, ptr);
> if (cnt != len)
> err = 1; <=== error happens here
> ...
>
> In the above particular case, len is 384 and cnt is 383.
>
> If user_data[384] is changed to
> char user_data[384] = {[0 ... 383] = 'a'};
>
> The above error will not happen and the test will run successfully.
>
> Cc: Mykyta Yatsenko <yatsenko@meta.com>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
> tools/testing/selftests/bpf/prog_tests/dynptr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c b/tools/testing/selftests/bpf/prog_tests/dynptr.c
> index 62e7ec775f24..4cc61afa63b4 100644
> --- a/tools/testing/selftests/bpf/prog_tests/dynptr.c
> +++ b/tools/testing/selftests/bpf/prog_tests/dynptr.c
> @@ -45,7 +45,7 @@ static struct {
>
> static void verify_success(const char *prog_name, enum test_setup_type setup_type)
> {
> - char user_data[384] = {[0 ... 382] = 'a', '\0'};
> + char user_data[384] = {[0 ... 383] = 'a'};
> struct dynptr_success *skel;
> struct bpf_program *prog;
> struct bpf_link *link;
This test is disabled in the DENYLIST and the fix was submitted to
another tree:
https://patchwork.kernel.org/project/linux-mm/patch/20250422131449.57177-1-mykyta.yatsenko5@gmail.com/
It's a little bit different problem.
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH bpf-next] selftests/bpf: Fix dynptr/test_probe_read_user_str_dynptr test failure
2025-05-16 16:03 ` Mykyta Yatsenko
@ 2025-05-16 16:23 ` Yonghong Song
0 siblings, 0 replies; 3+ messages in thread
From: Yonghong Song @ 2025-05-16 16:23 UTC (permalink / raw)
To: Mykyta Yatsenko, bpf
Cc: Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann, kernel-team,
Martin KaFai Lau, Mykyta Yatsenko
On 5/16/25 12:03 AM, Mykyta Yatsenko wrote:
> On 5/15/25 20:51, Yonghong Song wrote:
>> When running bpf selftests with llvm18 compiler, I hit the following
>> test failure:
>>
>> verify_success:PASS:dynptr_success__open 0 nsec
>> verify_success:PASS:bpf_object__find_program_by_name 0 nsec
>> verify_success:PASS:dynptr_success__load 0 nsec
>> verify_success:PASS:test_run 0 nsec
>> verify_success:FAIL:err unexpected err: actual 1 != expected 0
>> #91/19 dynptr/test_probe_read_user_str_dynptr:FAIL
>> #91 dynptr:FAIL
>>
>> I did some analysis and found that the test failure is related to
>> lib/strncpy_from_user.c function do_strncpy_from_user():
>>
>> ...
>> byte_at_a_time:
>> while (max) {
>> char c;
>>
>> unsafe_get_user(c,src+res, efault);
>> dst[res] = c;
>> if (!c)
>> return res;
>> res++;
>> max--;
>> }
>> ...
>>
>> Depending on whether the character 'c' is '\0' or not, the
>> return value 'res' could be different.
>>
>> In prog_tests/dynptr.c, we have
>> char user_data[384] = {[0 ... 382] = 'a', '\0'};
>> the user_data[383] is '\0'. This will cause the following
>> error in progs/dynptr_success.c:
>>
>> test_dynptr_probe_str_xdp:
>> ...
>> bpf_for(i, 0, ARRAY_SIZE(test_len)) {
>> __u32 len = test_len[i];
>>
>> cnt = bpf_read_dynptr_fn(&ptr_xdp, off, len, ptr);
>> if (cnt != len)
>> err = 1; <=== error happens here
>> ...
>>
>> In the above particular case, len is 384 and cnt is 383.
>>
>> If user_data[384] is changed to
>> char user_data[384] = {[0 ... 383] = 'a'};
>>
>> The above error will not happen and the test will run successfully.
>>
>> Cc: Mykyta Yatsenko <yatsenko@meta.com>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>> tools/testing/selftests/bpf/prog_tests/dynptr.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> b/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> index 62e7ec775f24..4cc61afa63b4 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/dynptr.c
>> @@ -45,7 +45,7 @@ static struct {
>> static void verify_success(const char *prog_name, enum
>> test_setup_type setup_type)
>> {
>> - char user_data[384] = {[0 ... 382] = 'a', '\0'};
>> + char user_data[384] = {[0 ... 383] = 'a'};
>> struct dynptr_success *skel;
>> struct bpf_program *prog;
>> struct bpf_link *link;
> This test is disabled in the DENYLIST and the fix was submitted to
> another tree:
> https://patchwork.kernel.org/project/linux-mm/patch/20250422131449.57177-1-mykyta.yatsenko5@gmail.com/
>
> It's a little bit different problem.
Okay. This works too. I thought about this earlier during investigation but decided not to change core kernel code...
^ permalink raw reply [flat|nested] 3+ messages in thread
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2025-05-15 19:51 [PATCH bpf-next] selftests/bpf: Fix dynptr/test_probe_read_user_str_dynptr test failure Yonghong Song
2025-05-16 16:03 ` Mykyta Yatsenko
2025-05-16 16:23 ` Yonghong Song
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