[PATCH v2] md: fix an incorrect NULL check in sync_sbs

[PATCH v2] md: fix an incorrect NULL check in sync_sbs

[Xiaomeng Tong]

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 using 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")
Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
---

changes since v1:
 - rephrase the subject (Guoqing Jiang)
 - add Acked-by: for Guoqing Jiang
v1:https://lore.kernel.org/lkml/20220327080002.11923-1-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)
-- 
2.17.1

Re: [PATCH v2] md: fix an incorrect NULL check in sync_sbs

[Song Liu]

On Mon, Mar 28, 2022 at 1:11 AM Xiaomeng Tong <xiam0nd.tong@gmail.com> 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 using the original variable 'pdev' as a dedicated pointer to

s/pdev/rdev/

> point to the found element.
>
> Cc: stable@vger.kernel.org
> Fixes: 2aa82191ac36c ("md-cluster: Perform a lazy update")

"Fixes" should use a hash of 12 characters (13 given here). Did
checkpatch.pl complain about it?

> Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
> ---
>
> changes since v1:
>  - rephrase the subject (Guoqing Jiang)
>  - add Acked-by: for Guoqing Jiang
> v1:https://lore.kernel.org/lkml/20220327080002.11923-1-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)
> --
> 2.17.1
>

Re: [PATCH v2] md: fix an incorrect NULL check in sync_sbs

[Xiaomeng Tong]

On Thu, 7 Apr 2022 17:36:48 -0700, Song Liu wrote:
> On Mon, Mar 28, 2022 at 1:11 AM Xiaomeng Tong <xiam0nd.tong@gmail.com> 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 using the original variable 'pdev' as a dedicated pointer to
> 
> s/pdev/rdev/
>
Have fixed it in PATCH v3, please check it. Thank you.

> 
> > point to the found element.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: 2aa82191ac36c ("md-cluster: Perform a lazy update")
> 
> "Fixes" should use a hash of 12 characters (13 given here). Did
> checkpatch.pl complain about it?

Have fixed it in PATCH v3, please check it. Thank you.

--
Xiaomeng Tong