Re: [PATCH -next v2 2/2] md/raid5-cache: fix null-ptr-deref in r5l_reclaim_thread()

[Song Liu <song@kernel.org>]

On Wed, Jun 28, 2023 at 9:08 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> r5l_reclaim_thread() already check that 'conf->log' is not NULL in the
> beginning, however, r5c_do_reclaim() and r5l_do_reclaim() will
> dereference 'conf->log' again, which will cause null-ptr-deref if
> 'conf->log' is set to NULL from r5l_exit_log() concurrently.

r5l_exit_log() will wait until reclaim_thread() finishes, and then set
conf->log to NULL. So this is not a problem, no?

Thanks,
Song

>
> Fix this problem by don't dereference 'conf->log' again in
> r5c_do_reclaim() and r5c_do_reclaim().
>
> Fixes: a39f7afde358 ("md/r5cache: write-out phase and reclaim support")
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  drivers/md/raid5-cache.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index 083288e36949..ba6fc146d265 100644
> --- a/drivers/md/raid5-cache.c
> +++ b/drivers/md/raid5-cache.c
> @@ -1148,10 +1148,9 @@ static void r5l_run_no_space_stripes(struct r5l_log *log)
>   * for write through mode, returns log->next_checkpoint
>   * for write back, returns log_start of first sh in stripe_in_journal_list
>   */
> -static sector_t r5c_calculate_new_cp(struct r5conf *conf)
> +static sector_t r5c_calculate_new_cp(struct r5l_log *log)
>  {
>         struct stripe_head *sh;
> -       struct r5l_log *log = conf->log;
>         sector_t new_cp;
>         unsigned long flags;
>
> @@ -1159,12 +1158,12 @@ static sector_t r5c_calculate_new_cp(struct r5conf *conf)
>                 return log->next_checkpoint;
>
>         spin_lock_irqsave(&log->stripe_in_journal_lock, flags);
> -       if (list_empty(&conf->log->stripe_in_journal_list)) {
> +       if (list_empty(&log->stripe_in_journal_list)) {
>                 /* all stripes flushed */
>                 spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
>                 return log->next_checkpoint;
>         }
> -       sh = list_first_entry(&conf->log->stripe_in_journal_list,
> +       sh = list_first_entry(&log->stripe_in_journal_list,
>                               struct stripe_head, r5c);
>         new_cp = sh->log_start;
>         spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
> @@ -1173,10 +1172,8 @@ static sector_t r5c_calculate_new_cp(struct r5conf *conf)
>
>  static sector_t r5l_reclaimable_space(struct r5l_log *log)
>  {
> -       struct r5conf *conf = log->rdev->mddev->private;
> -
>         return r5l_ring_distance(log, log->last_checkpoint,
> -                                r5c_calculate_new_cp(conf));
> +                                r5c_calculate_new_cp(log));
>  }
>
>  static void r5l_run_no_mem_stripe(struct r5l_log *log)
> @@ -1419,9 +1416,9 @@ void r5c_flush_cache(struct r5conf *conf, int num)
>         }
>  }
>
> -static void r5c_do_reclaim(struct r5conf *conf)
> +static void r5c_do_reclaim(struct r5l_log *log)
>  {
> -       struct r5l_log *log = conf->log;
> +       struct r5conf *conf = log->rdev->mddev->private;
>         struct stripe_head *sh;
>         int count = 0;
>         unsigned long flags;
> @@ -1496,7 +1493,6 @@ static void r5c_do_reclaim(struct r5conf *conf)
>
>  static void r5l_do_reclaim(struct r5l_log *log)
>  {
> -       struct r5conf *conf = log->rdev->mddev->private;
>         sector_t reclaim_target = xchg(&log->reclaim_target, 0);
>         sector_t reclaimable;
>         sector_t next_checkpoint;
> @@ -1525,7 +1521,7 @@ static void r5l_do_reclaim(struct r5l_log *log)
>                                     log->io_list_lock);
>         }
>
> -       next_checkpoint = r5c_calculate_new_cp(conf);
> +       next_checkpoint = r5c_calculate_new_cp(log);
>         spin_unlock_irq(&log->io_list_lock);
>
>         if (reclaimable == 0 || !write_super)
> @@ -1554,7 +1550,7 @@ static void r5l_reclaim_thread(struct md_thread *thread)
>
>         if (!log)
>                 return;
> -       r5c_do_reclaim(conf);
> +       r5c_do_reclaim(log);
>         r5l_do_reclaim(log);
>  }
>
> --
> 2.39.2
>