linux-kernel - Re: [PATCH] bpftool: Fix memory leak in do_build_table

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Date:   Tue, 6 Dec 2022 15:14:38 +0800
From:   Miaoqian Lin <linmq006@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Quentin Monnet <quentin@...valent.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpftool: Fix memory leak in do_build_table_cb

Hi, Daniel

On 2022/12/6 4:05, Daniel Borkmann wrote:
> On 12/5/22 9:13 AM, Miaoqian Lin wrote:
>> strdup() allocates memory for path. We need to release the memory in
>> the following error paths. Add free() to avoid memory leak.
>>
>> Fixes: 8f184732b60b ("bpftool: Switch to libbpf's hashmap for pinned paths of BPF objects")
>> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
>> ---
>>   tools/bpf/bpftool/common.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
>> index 0cdb4f711510..8a820356525e 100644
>> --- a/tools/bpf/bpftool/common.c
>> +++ b/tools/bpf/bpftool/common.c
>> @@ -499,9 +499,11 @@ static int do_build_table_cb(const char *fpath, const struct stat *sb,
>>       if (err) {
>>           p_err("failed to append entry to hashmap for ID %u, path '%s': %s",
>>                 pinned_info.id, path, strerror(errno));
>> -        goto out_close;
>> +        goto out_free;
>>       }
>>   +out_free:
>> +    free(path);
>
> It would be ok if you were to add the free(path) into the err condition, but here you
> also cause the !err to be freed which would trigger as UAF. See the hashmap_insert()
> where just set the pointer entry->value = <path>.. how was this tested before submission?
>
Thanks for your review. You're right. Sorry for the mistake, I meant to free it in the error path.

I'll send v2 to fix this. I spotted it with static detection tool.

>>   out_close:
>>       close(fd);
>>   out_ret:
>>
>