Re: [PATCH] net: sched: fix possible OOB write in fl_set_geneve_opt()

[Pieter Jansen van Vuuren]

On 30/05/2023 12:36, Simon Horman wrote:
> [Updated Pieter's email address, dropped old email address of mine]

Thank you Simon.

> 
> On Mon, May 29, 2023 at 12:36:15PM +0800, Hangyu Hua wrote:
>> If we send two TCA_FLOWER_KEY_ENC_OPTS_GENEVE packets and their total
>> size is 252 bytes(key->enc_opts.len = 252) then
>> key->enc_opts.len = opt->length = data_len / 4 = 0 when the third
>> TCA_FLOWER_KEY_ENC_OPTS_GENEVE packet enters fl_set_geneve_opt. This
>> bypasses the next bounds check and results in an out-of-bounds.
>>
>> Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
>> Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
> 
> Hi Hangyu Hua,
> 
> Thanks. I think I see the problem too.
> But I do wonder, is this more general than Geneve options?
> That is, can this occur with any sequence of options, that
> consume space in enc_opts (configured in fl_set_key()) that
> in total are more than 256 bytes?
> 

Hi Hangyu Hua,

Thank you for the patch. In addition to Simon's comment; I think the subject
headline should include net, i.e. [PATCH net]. Also could you please provide
an example tc filter add dev... command to replicate the issue? (Just to make
it a bit easier to understand).

>> ---
>>  net/sched/cls_flower.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
>> index e960a46b0520..a326fbfe4339 100644
>> --- a/net/sched/cls_flower.c
>> +++ b/net/sched/cls_flower.c
>> @@ -1153,6 +1153,9 @@ static int fl_set_geneve_opt(const struct nlattr *nla, struct fl_flow_key *key,
>>  	if (option_len > sizeof(struct geneve_opt))
>>  		data_len = option_len - sizeof(struct geneve_opt);
>>  
>> +	if (key->enc_opts.len > FLOW_DIS_TUN_OPTS_MAX - 4)
>> +		return -ERANGE;
>> +
>>  	opt = (struct geneve_opt *)&key->enc_opts.data[key->enc_opts.len];
>>  	memset(opt, 0xff, option_len);
>>  	opt->length = data_len / 4;
>> -- 
>> 2.34.1
>>
>>