linux-kernel - Re: [bpf-next] bpf: use kvmemdup

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Date:   Tue, 13 Sep 2022 12:24:08 +0800
From:   wangyufen <wangyufen@...wei.com>
To:     <sdf@...gle.com>
CC:     <ast@...nel.org>, <daniel@...earbox.net>,
        <john.fastabend@...il.com>, <andrii@...nel.org>,
        <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
        <kpsingh@...nel.org>, <haoluo@...gle.com>, <jolsa@...nel.org>,
        <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [bpf-next] bpf: use kvmemdup_bpfptr helper


在 2022/9/10 1:27, sdf@...gle.com 写道:
> On 09/09, Wang Yufen wrote:
>> Use kvmemdup_bpfptr helper instead of open-coding to
>> simplify the code.
>
>> Signed-off-by: Wang Yufen <wangyufen@...wei.com>
>> ---
>>   kernel/bpf/syscall.c | 14 ++++----------
>>   1 file changed, 4 insertions(+), 10 deletions(-)
>
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index 4e9d4622aef7..13ce28081982 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -1413,20 +1413,14 @@ static int map_update_elem(union bpf_attr 
>> *attr, bpfptr_t uattr)
>>       }
>
>>       value_size = bpf_map_value_size(map);
>> -
>> -    err = -ENOMEM;
>> -    value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
>> -    if (!value)
>> +    value = kvmemdup_bpfptr(uvalue, value_size);
>> +    if (IS_ERR(value)) {
>> +        err = PTR_ERR(value);
>>           goto free_key;
>> -
>> -    err = -EFAULT;
>> -    if (copy_from_bpfptr(value, uvalue, value_size) != 0)
>> -        goto free_value;
>> +    }
>
>>       err = bpf_map_update_value(map, f, key, value, attr->flags);
>
>
> [..]
>
>> -free_value:
>> -    kvfree(value);
>
> And here you leak the value. We need to free it after update regardless
> of error/success. That's why it is coded like that.

Thanks for your comments.

It's my mistake.

Can I keep kvfree(value);    and send v2?

>
>>   free_key:
>>       kvfree(key);
>>   err_put:
>> -- 
>> 2.25.1
>