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

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

[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 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)
-- 
2.17.1

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

[Guoqing Jiang]

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