Re: [PATCH v3] md: fix an incorrect NULL check in md_reload_sb

[Song Liu]

On Fri, Apr 8, 2022 at 1:47 AM Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx> wrote:
>
> The bug is here:
>         if (!rdev || rdev->desc_nr != nr) {
>
> The list iterator value 'rdev' will *always* be set and non-NULL
> by rdev_for_each_rcu(), so it is incorrect to assume that the
> iterator value will be NULL if the list is empty or no element
> found (In fact, it will be a bogus pointer to an invalid struct
> object containing the HEAD). Otherwise it will bypass the check
> and lead to invalid memory access passing the check.
>
> To fix the bug, use a new variable 'iter' as the list iterator,
> while using the original variable 'pdev' as a dedicated pointer to
> point to the found element.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 70bcecdb1534 ("md-cluster: Improve md_reload_sb to be less error prone")
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>

Applied to md-next. Thanks!