Re: [PATCH] md: md1: fix an incorrect NULL check on list iterator

[Guoqing Jiang <guoqing.jiang@linux.dev>]

The subject need to be improved as well.

On 3/27/22 4:00 PM, Xiaomeng Tong wrote:
> The bug is here:
> 	if (!rdev)
>
> The list iterator value 'rdev' will *always* be set and non-NULL
> by rdev_for_each(), so it is incorrect to assume that the iterator
> value will be NULL if the list is empty or no element found.
> Otherwise it will bypass the NULL check and lead to invalid memory
> access passing the check.
>
> To fix the bug, use a new variable 'iter' as the list iterator,
> while use the original variable 'pdev' as a dedicated pointer to
> point to the found element.
>
> Cc:stable@vger.kernel.org
> Fixes: 2aa82191ac36c ("md-cluster: Perform a lazy update")
> Signed-off-by: Xiaomeng Tong<xiam0nd.tong@gmail.com>
> ---
>   drivers/md/md.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 4d38bd7dadd6..7476fc204172 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -2629,14 +2629,16 @@ static void sync_sbs(struct mddev *mddev, int nospares)
>   
>   static bool does_sb_need_changing(struct mddev *mddev)
>   {
> -	struct md_rdev *rdev;
> +	struct md_rdev *rdev = NULL, *iter;
>   	struct mdp_superblock_1 *sb;
>   	int role;
>   
>   	/* Find a good rdev */
> -	rdev_for_each(rdev, mddev)
> -		if ((rdev->raid_disk >= 0) && !test_bit(Faulty, &rdev->flags))
> +	rdev_for_each(iter, mddev)
> +		if ((iter->raid_disk >= 0) && !test_bit(Faulty, &iter->flags)) {
> +			rdev = iter;
>   			break;
> +		}
>   
>   	/* No good device found. */
>   	if (!rdev)


Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>

Thanks,
Guoqing