Re: [PATCH V1] block: Fix null pointer dereference issue on struct io_cq

[Chaitanya Kulkarni]

On 5/17/23 01:44, Pradeep P V K wrote:
> There is a potential race between ioc_clear_fn() and
> exit_io_context() as shown below, due to which below
> crash is observed. It can also result into use-after-free
> issue.
>
> context#1:                           context#2:
> ioc_release_fn()                     do_exit();
> ->spin_lock(&ioc->lock);             ->exit_io_context();
> ->ioc_destroy_icq(icq);              ->ioc_exit_icqs();
>   ->list_del_init(&icq->q_node);       ->spin_lock_irq(&ioc->lock);
>   ->call_rcu(&icq->__rcu_head,
>       icq_free_icq_rcu);
> ->spin_unlock(&ioc->lock);
>                                        ->ioc_exit_icq(); gets the same icq
> 				       ->bfq_exit_icq();
>                                    This results into below crash as bic
> 				  is NULL as it is derived from icq.
> 				  There is a chance that icq could be
> 				  free'd as well.
>
> [33.245722][ T8666] Unable to handle kernel NULL pointer dereference
> at virtual address 0000000000000018.
> ...
> Call trace:
> [33.325782][ T8666]  bfq_exit_icq+0x28/0xa8
> [33.325785][ T8666]  exit_io_context+0xcc/0x100
> [33.325786][ T8666]  do_exit+0x764/0xa58
> [33.325791][ T8666]  do_group_exit+0x0/0xa0
> [33.325793][ T8666]  invoke_syscall+0x48/0x114
> [33.325802][ T8666]  el0_svc_common+0xcc/0x118
> [33.325805][ T8666]  do_el0_svc+0x34/0xd0
> [33.325807][ T8666]  el0_svc+0x38/0xd0
> [33.325812][ T8666]  el0t_64_sync_handler+0x8c/0xfc
> [33.325813][ T8666]  el0t_64_sync+0x1a0/0x1a4
>
> Fix this by checking with ICQ_DESTROYED flags in ioc_exit_icqs().
> Also, ensure ioc_exit_icq() is accessing icq within rcu_read_lock/unlock
> so that icq doesn't get free'd up while it is still using it.
>
> Signed-off-by: Pradeep P V K <quic_pragalla@xxxxxxxxxxx>
> ---

Is it possible to add a null_blk based blktests for this ?

-ck