netdev - Re: [PATCH] net: fix NULL pointer reference in cipso_v4_doi

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Date:   Mon, 30 Aug 2021 18:20:19 +0800
From:   王贇 <yun.wang@...ux.alibaba.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: fix NULL pointer reference in cipso_v4_doi_free

Hi, Paul

I'm sorry for missing this mail since my stupid filter rules...

Will send a new one soon as you suggested :-)

Regards,
Michael Wang

On 2021/8/27 上午8:09, Paul Moore wrote:
[snip]
>>
>> Reported-by: Abaci <abaci@...ux.alibaba.com>
>> Signed-off-by: Michael Wang <yun.wang@...ux.alibaba.com>
>> ---
>>
>>  net/ipv4/cipso_ipv4.c | 18 ++++++++++--------
>>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> Thanks for the problem report.  It's hard to say for certain due to
> the abbreviated backtrace without line number information, but it
> looks like the problem you are describing is happening when the
> allocation for doi_def->map.std fails near the top of
> netlbl_cipsov4_add_std() which causes the function to jump the
> add_std_failure target which ends up calling cipso_v4_doi_free().
> 
>   doi_def = kmalloc(sizeof(*doi_def), GFP_KERNEL);
>   if (doi_def == NULL)
>     return -ENOMEM;
>   doi_def->map.std = kzalloc(sizeof(*doi_def->map.std), GFP_KERNEL);
>   if (doi_def->map.std == NULL) {
>     ret_val = -ENOMEM;
>     goto add_std_failure;
>   }
>   ...
>   add_std_failure:
>     cipso_v4_doi_free(doi_def);
> 
> Since the doi_def allocation is not zero'd out, it is possible that
> the doi_def->type value could have a value of CIPSO_V4_MAP_TRANS when
> the doi_def->map.std allocation fails, causing the NULL pointer deref
> in cipso_v4_doi_free().  As this is the only case where we would see a
> problem like this, I suggest a better solution would be to change the
> if-block following the doi_def->map.std allocation to something like
> this:
> 
>   doi_def->map.std = kzalloc(sizeof(*doi_def->map.std), GFP_KERNEL);
>   if (doi_def->map.std == NULL) {
>     kfree(doi_def);
>     return -ENOMEM;
>   }
> 
>> diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
>> index 099259f..7fbd0b5 100644
>> --- a/net/ipv4/cipso_ipv4.c
>> +++ b/net/ipv4/cipso_ipv4.c
>> @@ -465,14 +465,16 @@ void cipso_v4_doi_free(struct cipso_v4_doi *doi_def)
>>         if (!doi_def)
>>                 return;
>>
>> -       switch (doi_def->type) {
>> -       case CIPSO_V4_MAP_TRANS:
>> -               kfree(doi_def->map.std->lvl.cipso);
>> -               kfree(doi_def->map.std->lvl.local);
>> -               kfree(doi_def->map.std->cat.cipso);
>> -               kfree(doi_def->map.std->cat.local);
>> -               kfree(doi_def->map.std);
>> -               break;
>> +       if (doi_def->map.std) {
>> +               switch (doi_def->type) {
>> +               case CIPSO_V4_MAP_TRANS:
>> +                       kfree(doi_def->map.std->lvl.cipso);
>> +                       kfree(doi_def->map.std->lvl.local);
>> +                       kfree(doi_def->map.std->cat.cipso);
>> +                       kfree(doi_def->map.std->cat.local);
>> +                       kfree(doi_def->map.std);
>> +                       break;
>> +               }
>>         }
>>         kfree(doi_def);
>>  }
>> --
>> 1.8.3.1
>>
> 
>