Re: [PATCH v1] Fix NULL pointer dereference in cn_filter()

[Anjali Kulkarni]

> On Oct 17, 2023, at 1:02 AM, Simon Horman <horms@xxxxxxxxxx> wrote:
> 
> On Fri, Oct 13, 2023 at 03:56:19PM -0700, Anjali Kulkarni wrote:
>> Check that sk_user_data is not NULL, else return from cn_filter().
> 
> Thanks,
> 
> I agree that this change seems likely to address the problem at the link
> below. And I also think cn_filter() is a good place to fix this [1].
> But I am wondering if you could add some commentary to the patch
> description, describing under what circumstances this problem can occur.

Thanks for reviewing! Yes, it seems this patch has fixed the issue (as tested by Oliver Sang). I will add some description for when this problem can occur in the next patch revision.

> 
> [1] https://urldefense.com/v3/__https://lore.kernel.org/all/20231013120105.GH29570@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!NNsMHaho3lyW2NyoT8Sju1BL78S5pNu5AhtZC76cc1Xb1_psXwfP0lmVtVmTxGRrsQkzClWNS8HriosTMols$ 
> 
>> Fixes: 2aa1f7a1f47c ("connector/cn_proc: Add filtering to fix some bugs")
>> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
>> Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-lkp/202309201456.84c19e27-oliver.sang@xxxxxxxxx/__;!!ACWV5N9M2RV99hQ!NNsMHaho3lyW2NyoT8Sju1BL78S5pNu5AhtZC76cc1Xb1_psXwfP0lmVtVmTxGRrsQkzClWNS8HrirVfNms7$ 
>> Signed-off-by: Anjali Kulkarni <anjali.k.kulkarni@xxxxxxxxxx>
>> ---
>> drivers/connector/cn_proc.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
>> index 05d562e9c8b1..a8e55569e4f5 100644
>> --- a/drivers/connector/cn_proc.c
>> +++ b/drivers/connector/cn_proc.c
>> @@ -54,7 +54,7 @@ static int cn_filter(struct sock *dsk, struct sk_buff *skb, void *data)
>> enum proc_cn_mcast_op mc_op;
>> uintptr_t val;
>> 
>> - if (!dsk || !data)
>> + if (!dsk || !data || !dsk->sk_user_data)
>> return 0;
>> 
>> ptr = (__u32 *)data;
>> -- 
>> 2.42.0
>>