From: Yu Kuai <yukuai3@huawei.com>

In raid10_run() if raid10_set_queue_limits() succeed, the return value
is set to zero, and if following procedures failed raid10_run() will
return zero while mddev->private is still NULL, causing null ptr
dereference in raid10_size().

Fix the problem by only overwrite the return value if
raid10_set_queue_limits() failed.

Fixes: 3d8466ba68d4 ("md/raid10: use the atomic queue limit update APIs")
Reported-and-tested-by: ValdikSS <iam@valdikss.org.ru>
Closes: https://lore.kernel.org/all/0dd96820-fe52-4841-bc58-dbf14d6bfcc8@valdikss.org.ru/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/raid10.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index f3bf1116794a..862b1fb71d86 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4061,9 +4061,12 @@ static int raid10_run(struct mddev *mddev)
 	}
 
 	if (!mddev_is_dm(conf->mddev)) {
-		ret = raid10_set_queue_limits(mddev);
-		if (ret)
+		int err = raid10_set_queue_limits(mddev);
+
+		if (err) {
+			ret = err;
 			goto out_free_conf;
+		}
 	}
 
 	/* need to check that every block has at least one working mirror */
-- 
2.39.2

On Tue, Oct 8, 2024 at 6:51 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> In raid10_run() if raid10_set_queue_limits() succeed, the return value
> is set to zero, and if following procedures failed raid10_run() will
> return zero while mddev->private is still NULL, causing null ptr
> dereference in raid10_size().
>
> Fix the problem by only overwrite the return value if
> raid10_set_queue_limits() failed.
>
> Fixes: 3d8466ba68d4 ("md/raid10: use the atomic queue limit update APIs")
> Reported-and-tested-by: ValdikSS <iam@valdikss.org.ru>
> Closes: https://lore.kernel.org/all/0dd96820-fe52-4841-bc58-dbf14d6bfcc8@valdikss.org.ru/
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Applied to md-6.12.

Thanks for the fix!
Song

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>