linux-kernel - Re: [PATCH bpf] bpf: Fix offset calculation error in __copy_map_value and zero_map

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Message-ID: <1ca2e4e8-ed7e-9174-01f6-c14539b8b8b2@huawei.com>
Date:   Sat, 12 Nov 2022 18:25:09 +0800
From:   Xu Kuohai <xukuohai@...wei.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>, <sdf@...gle.com>
CC:     Xu Kuohai <xukuohai@...weicloud.com>, <bpf@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH bpf] bpf: Fix offset calculation error in __copy_map_value
 and zero_map_value

On 11/12/2022 4:45 AM, Kumar Kartikeya Dwivedi wrote:
> On Sat, Nov 12, 2022 at 12:47:52AM IST, sdf@...gle.com wrote:
>> On 11/11, Xu Kuohai wrote:
>>> From: Xu Kuohai <xukuohai@...wei.com>
>>
>>> Function __copy_map_value and zero_map_value miscalculated copy offset,
>>> resulting in possible copy of unwanted data to user or kernel.
>>
>>> Fix it.
>>
>>> Fixes: cc48755808c6 ("bpf: Add zero_map_value to zero map value with
>>> special fields")
>>> Fixes: 4d7d7f69f4b1 ("bpf: Adapt copy_map_value for multiple offset case")
>>> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
>>> ---
>>>    include/linux/bpf.h | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>
>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>> index 74c6f449d81e..c1bd1bd10506 100644
>>> --- a/include/linux/bpf.h
>>> +++ b/include/linux/bpf.h
>>> @@ -315,7 +315,7 @@ static inline void __copy_map_value(struct bpf_map
>>> *map, void *dst, void *src, b
>>>    		u32 next_off = map->off_arr->field_off[i];
>>
>>>    		memcpy(dst + curr_off, src + curr_off, next_off - curr_off);
>>> -		curr_off += map->off_arr->field_sz[i];
>>> +		curr_off = next_off + map->off_arr->field_sz[i];
>>>    	}
>>>    	memcpy(dst + curr_off, src + curr_off, map->value_size - curr_off);
>>>    }
>>> @@ -344,7 +344,7 @@ static inline void zero_map_value(struct bpf_map
>>> *map, void *dst)
>>>    		u32 next_off = map->off_arr->field_off[i];
>>
>>>    		memset(dst + curr_off, 0, next_off - curr_off);
>>> -		curr_off += map->off_arr->field_sz[i];
>>> +		curr_off = next_off + map->off_arr->field_sz[i];
>>>    	}
>>>    	memset(dst + curr_off, 0, map->value_size - curr_off);
>>>    }
>>
>> Hmm, does it mean that it currently works only for the cases where
>> these special fields are first/last?
>>
>> Also, what about bpf-next? The same problem seem to exist there?
>>
> 
> Replied with the patch in the other email.
> 
>> Might be a good idea to have some selftest to exercise this?
>>
> 
> I agree, there was another bug in the same code before this, so I think we
> should add tests for this (I should have done that with the commit being
> fixed...).
> 
> Xu, if you have cycles, can you work on testing a few edge cases and make sure
> we don't regress in the future? Otherwise I will take a look next week.
> .

Ok, I'll add a few cases to test_sk_storage_map to capture this