Re: [PATCH v2 1/4] md/raid10: fix null-ptr-deref of mreplace in raid10_sync_request

[Song Liu]

On Fri, May 26, 2023 at 12:47 AM <linan666@xxxxxxxxxxxxxxx> wrote:
>
> From: Li Nan <linan122@xxxxxxxxxx>
>
> need_replace will be set to 1 if no-Faulty mreplace exists, and mreplace
> will be deref later. However, the latter check of mreplace might set
> mreplace to NULL, null-ptr-deref occurs if need_replace is 1 at this time.
>
> Fix it by merging two checks into one. And replace 'need_replace' with
> 'mreplace' because their values are always the same.
>
> Fixes: ee37d7314a32 ("md/raid10: Fix raid10 replace hang when new added disk faulty")
> Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
> ---
>  drivers/md/raid10.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 4fcfcb350d2b..e21502c03b45 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -3438,7 +3438,6 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>                         int must_sync;
>                         int any_working;
>                         int need_recover = 0;
> -                       int need_replace = 0;
>                         struct raid10_info *mirror = &conf->mirrors[i];
>                         struct md_rdev *mrdev, *mreplace;
>
> @@ -3451,10 +3450,10 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>                             !test_bit(In_sync, &mrdev->flags))
>                                 need_recover = 1;
>                         if (mreplace != NULL &&
> -                           !test_bit(Faulty, &mreplace->flags))
> -                               need_replace = 1;
> +                           test_bit(Faulty, &mreplace->flags))
> +                               mreplace = NULL;
>
> -                       if (!need_recover && !need_replace) {
> +                       if (!need_recover && !mreplace) {
>                                 rcu_read_unlock();
>                                 continue;
>                         }
> @@ -3470,8 +3469,6 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>                                 rcu_read_unlock();
>                                 continue;
>                         }

To make sure I understand the issue correctly:

The null-ptr-deref only happens when the Faulty bit was set after the
last check and before this check below, right?

> -                       if (mreplace && test_bit(Faulty, &mreplace->flags))
> -                               mreplace = NULL;
>                         /* Unless we are doing a full sync, or a replacement
>                          * we only need to recover the block if it is set in
>                          * the bitmap

Thanks,
Song

> @@ -3594,11 +3591,11 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>                                 bio = r10_bio->devs[1].repl_bio;
>                                 if (bio)
>                                         bio->bi_end_io = NULL;
> -                               /* Note: if need_replace, then bio
> +                               /* Note: if replace is not NULL, then bio
>                                  * cannot be NULL as r10buf_pool_alloc will
>                                  * have allocated it.
>                                  */
> -                               if (!need_replace)
> +                               if (!mreplace)
>                                         break;
>                                 bio->bi_next = biolist;
>                                 biolist = bio;
> --
> 2.31.1
>