Re: [PATCH] block, bfq: fix uaf for bfqq in bic_set_bfqq()

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

On 2023-02-21 08:04, Yu Kuai wrote:
> Hi, Jens
> 
> 在 2023/01/13 17:44, Yu Kuai 写道:
>> After commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'"),
>> bic->bfqq will be accessed in bic_set_bfqq(), however, in some context
>> bic->bfqq will be freed first, and bic_set_bfqq() is called with the freed
>> bic->bfqq.
>>
>> Fix the problem by always freeing bfqq after bic_set_bfqq().
>>
>> Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
>> Reported-and-tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   block/bfq-cgroup.c  | 2 +-
>>   block/bfq-iosched.c | 4 +++-
>>   2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
>> index a6e8da5f5cfd..feb13ac25557 100644
>> --- a/block/bfq-cgroup.c
>> +++ b/block/bfq-cgroup.c
>> @@ -749,8 +749,8 @@ static void bfq_sync_bfqq_move(struct bfq_data *bfqd,
>>            * old cgroup.
>>            */
>>           bfq_put_cooperator(sync_bfqq);
>> -        bfq_release_process_ref(bfqd, sync_bfqq);
>>           bic_set_bfqq(bic, NULL, true, act_idx);
>> +        bfq_release_process_ref(bfqd, sync_bfqq);
>>       }
>>   }
>>
> 
> It seems this change is missed in GIT PULL for-6.3. I'll send a seperate
> patch to fix this...
> 

It was already applied in time for 6.2 as b600de2d7d3a16f9007fad1bdae82a3951a26af2
and also already merged to 6.1-stable.

cheers
Holger