Re: [PATCH v2] md: add mddev->pers to avoid potential NULL pointer dereference

[NeilBrown <neilb@suse.com>]

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On Tue, Apr 02 2019, Yufen Yu wrote:

> When doing re-add, we need to ensure rdev->mddev->pers is not NULL,
> which can avoid potential NULL pointer derefence in fallowing
> add_bound_rdev().
>
> Fixes: a6da4ef85cef ("md: re-add a failed disk")
> Cc: Xiao Ni <xni@redhat.com>
> Cc: NeilBrown <neilb@suse.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Yufen Yu <yuyufen@huawei.com>

Reviewed-by: NeilBrown <neilb@suse.com>

Thanks,
NeilBrown

> ---
>  drivers/md/md.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 875b29ba5926..66b6bdf9f364 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -2859,8 +2859,10 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
>  			err = 0;
>  		}
>  	} else if (cmd_match(buf, "re-add")) {
> -		if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk == -1) &&
> -			rdev->saved_raid_disk >= 0) {
> +		if (!rdev->mddev->pers)
> +			err = -EINVAL;
> +		else if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk == -1) &&
> +				rdev->saved_raid_disk >= 0) {
>  			/* clear_bit is performed _after_ all the devices
>  			 * have their local Faulty bit cleared. If any writes
>  			 * happen in the meantime in the local node, they
> -- 
> 2.16.2.dirty

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