linux-kernel - Re: [PATCH] selftests/bpf: close the file descriptor to avoid resource leaks

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Message-ID: <e255897a-30d8-5745-b89b-eb801e0864a9@huaweicloud.com>
Date: Mon, 7 Apr 2025 09:36:52 +0800
From: Hou Tao <houtao@...weicloud.com>
To: malaya kumar rout <malayarout91@...il.com>,
 Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, Geliang Tang <geliang@...nel.org>,
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/bpf: close the file descriptor to avoid
 resource leaks

Hi,

On 4/5/2025 1:59 PM, malaya kumar rout wrote:
> On Fri, Apr 4, 2025 at 9:22 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
>> On Sun, Mar 23, 2025 at 11:43 PM Malaya Kumar Rout
>> <malayarout91@...il.com> wrote:
>>> Static Analyis for bench_htab_mem.c with cppcheck:error
>>> tools/testing/selftests/bpf/benchs/bench_htab_mem.c:284:3:
>>> error: Resource leak: fd [resourceLeak]
>>> tools/testing/selftests/bpf/prog_tests/sk_assign.c:41:3:
>>> error: Resource leak: tc [resourceLeak]
>>>
>>> fix the issue  by closing the file descriptor (fd & tc) when
>>> read & fgets operation fails.
>>>
>>> Signed-off-by: Malaya Kumar Rout <malayarout91@...il.com>
>>> ---
>>>  tools/testing/selftests/bpf/benchs/bench_htab_mem.c | 1 +
>>>  tools/testing/selftests/bpf/prog_tests/sk_assign.c  | 4 +++-
>>>  2 files changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/tools/testing/selftests/bpf/benchs/bench_htab_mem.c b/tools/testing/selftests/bpf/benchs/bench_htab_mem.c
>>> index 926ee822143e..59746fd2c23a 100644
>>> --- a/tools/testing/selftests/bpf/benchs/bench_htab_mem.c
>>> +++ b/tools/testing/selftests/bpf/benchs/bench_htab_mem.c
>>> @@ -281,6 +281,7 @@ static void htab_mem_read_mem_cgrp_file(const char *name, unsigned long *value)
>>>         got = read(fd, buf, sizeof(buf) - 1);
>> It could be a bit cleaner to add close(fd) here and drop the one we
>> have at the end of the function.
>>
> Here, close(fd)  is now positioned within the error handling block,
> guaranteeing that
> the file descriptor will be closed prior to returning from the
> function in the event of a read error.
> Meanwhile, the final close(fd) at the end of the function is retained
> for successful execution,
> thereby avoiding any potential resource leaks.
> Hence, It is essential to add the close(fd) in both locations to
> prevent resource leakage.

I think Andrii was proposing the following solution:

{
        /* ...... */
        got = read(fd, buf, sizeof(buf) - 1);
        close(fd);
        if (got <= 0) {
                *value = 0;
                return;
        }
        buf[got] = 0;

        *value = strtoull(buf, NULL, 0);
}

It only invokes close(fd) once to handle both the failed case and the
successful case.
>
>> pw-bot: cr
>>
>>>         if (got <= 0) {
>>>                 *value = 0;
>>> +               close(fd);
>>>                 return;
>>>         }
>>>         buf[got] = 0;
>>> diff --git a/tools/testing/selftests/bpf/prog_tests/sk_assign.c b/tools/testing/selftests/bpf/prog_tests/sk_assign.c
>>> index 0b9bd1d6f7cc..10a0ab954b8a 100644
>>> --- a/tools/testing/selftests/bpf/prog_tests/sk_assign.c
>>> +++ b/tools/testing/selftests/bpf/prog_tests/sk_assign.c
>>> @@ -37,8 +37,10 @@ configure_stack(void)
>>>         tc = popen("tc -V", "r");
>>>         if (CHECK_FAIL(!tc))
>>>                 return false;
>>> -       if (CHECK_FAIL(!fgets(tc_version, sizeof(tc_version), tc)))
>>> +       if (CHECK_FAIL(!fgets(tc_version, sizeof(tc_version), tc))) {
>>> +               pclose(tc);
>> this one looks good
>>
>>>                 return false;
>>> +       }
>>>         if (strstr(tc_version, ", libbpf "))
>>>                 prog = "test_sk_assign_libbpf.bpf.o";
>>>         else
>>> --
>>> 2.43.0
>>>
> .