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

[Xiao Ni <xni@xxxxxxxxxx>]

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);
 }

 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
> >