Re: [PATCH] md: fix null-ptr-deference in md_free_disk()

[Yu Kuai]

Hi,

在 2023/02/22 8:41, Xiao Ni 写道:
> Sorry, the patch was missed in the last email.
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 927a43db5dfb..f5480778e2f7 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -6256,6 +6256,11 @@ static void __md_stop(struct mddev *mddev)
>                  mddev->to_remove = &md_redundancy_group;
>          module_put(pers->owner);
>          clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
> +
> +       percpu_ref_exit(&mddev->writes_pending);
> +       percpu_ref_exit(&mddev->active_io);
> +       bioset_exit(&mddev->bio_set);
> +       bioset_exit(&mddev->sync_set);
>   }

This change pass my test, feel free to add:
Tested-by: Yu Kuai <yukuai3@xxxxxxxxxx>

>   void md_stop(struct mddev *mddev)
> @@ -6265,10 +6270,6 @@ void md_stop(struct mddev *mddev)
>           */
>          __md_stop_writes(mddev);
>          __md_stop(mddev);
> -       percpu_ref_exit(&mddev->writes_pending);
> -       percpu_ref_exit(&mddev->active_io);
> -       bioset_exit(&mddev->bio_set);
> -       bioset_exit(&mddev->sync_set);
>   }
>
>   EXPORT_SYMBOL_GPL(md_stop);
> @@ -7839,11 +7840,6 @@ static void md_free_disk(struct gendisk *disk)
>   {
>          struct mddev *mddev = disk->private_data;
>
> -       percpu_ref_exit(&mddev->writes_pending);
> -       percpu_ref_exit(&mddev->active_io);
> -       bioset_exit(&mddev->bio_set);
> -       bioset_exit(&mddev->sync_set);
> -
>          mddev_free(mddev);
>   }
>
> If we release those memories in md_free_disk, it's hard to find the
> corresponding relationship between alloc memory and free memory.
> If we free memory in __md_stop, it's easy to find the right place where
> those memories are free.
>
> Best Regards
> Xiao
>
>
> On Wed, Feb 22, 2023 at 8:39 AM Xiao Ni <xni@xxxxxxxxxx> wrote:
> > Hi Yu Kuai
> >
> > Thanks for reporting this problem.
> >
> > For creating raid device, md raid calls do_md_run->md_run, dm raid
> > calls md_run. We alloc those memory in md_run.
> > For stopping raid device, md raid calls do_md_stop->__md_stop, dm raid
> > calls md_stop->__md_stop.
> >
> > So how about this patch:
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 927a43db5dfb..f5480778e2f7 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> >
> > On Tue, Feb 21, 2023 at 9:33 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> > >
> > > If md_run() failed after 'acitive_io' is initialized, then
> > > percpu_ref_exit() is called in error path, however, later md_free_disk()
> > > will call percpu_ref_exit() again, which lead to following
> > > null-ptr-deference:
> > >
> > > BUG: kernel NULL pointer dereference, address: 0000000000000038
> > > Oops: 0000 [#1] PREEMPT SMP
> > > CPU: 41 PID: 585 Comm: kworker/41:1 Not tainted 6.2.0-rc8-next-20230220 #1452
> > > Workqueue: md_misc mddev_delayed_delete
> > > RIP: 0010:free_percpu+0x110/0x630
> > > Call Trace:
> > >   <TASK>
> > >   __percpu_ref_exit+0x44/0x70
> > >   percpu_ref_exit+0x16/0x90
> > >   md_free_disk+0x2f/0x80
> > >   disk_release+0x101/0x180
> > >   device_release+0x84/0x110
> > >   kobject_put+0x12a/0x380
> > >   kobject_put+0x160/0x380
> > >   mddev_delayed_delete+0x19/0x30
> > >   process_one_work+0x269/0x680
> > >   worker_thread+0x266/0x640
> > >   kthread+0x151/0x1b0
> > >   ret_from_fork+0x1f/0x30
> > >
> > > Since freeing mddev will exit 'active_io' unconditionally, fix the
> > > problem by removing exiting 'active_io' from error path, this way
> > > it will be delayed to free mddev.
> > >
> > > Fixes: 72adae23a72c ("md: Change active_io to percpu")
> > > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > > ---
> > >   drivers/md/md.c | 4 +---
> > >   1 file changed, 1 insertion(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > > index 927a43db5dfb..77124679b3fd 100644
> > > --- a/drivers/md/md.c
> > > +++ b/drivers/md/md.c
> > > @@ -5851,7 +5851,7 @@ int md_run(struct mddev *mddev)
> > >          if (!bioset_initialized(&mddev->bio_set)) {
> > >                  err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
> > >                  if (err)
> > > -                       goto exit_active_io;
> > > +                       return err;
> > >          }
> > >          if (!bioset_initialized(&mddev->sync_set)) {
> > >                  err = bioset_init(&mddev->sync_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
> > > @@ -6039,8 +6039,6 @@ int md_run(struct mddev *mddev)
> > >          bioset_exit(&mddev->sync_set);
> > >   exit_bio_set:
> > >          bioset_exit(&mddev->bio_set);
> > > -exit_active_io:
> > > -       percpu_ref_exit(&mddev->active_io);
> > >          return err;
> > >   }
> > >   EXPORT_SYMBOL_GPL(md_run);
> > > --
> > > 2.31.1
>
> .