Hi Xiaomeng,

I'd suggest to rephrase the subject to "md: fix an incorrect NULL check in md_reload_sb".

On 3/27/22 4:01 PM, Xiaomeng Tong 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 use the original variable 'pdev' as a dedicated pointer to point to the found element.

Cc:stable@vger.kernel.org Fixes: 70bcecdb1534 ("amd-cluster: Improve md_reload_sb to be less error prone")

amd-cluster? 😉

Signed-off-by: Xiaomeng Tongxiam0nd.tong@gmail.com

drivers/md/md.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c index 7476fc204172..f156678c08bc 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -9794,16 +9794,18 @@ static int read_rdev(struct mddev *mddev, struct md_rdev *rdev) void md_reload_sb(struct mddev *mddev, int nr) {

• struct md_rdev *rdev;

• struct md_rdev *rdev = NULL, *iter; int err;

/* Find the rdev */

• rdev_for_each_rcu(rdev, mddev) {

• if (rdev->desc_nr == nr)
  

• rdev_for_each_rcu(iter, mddev) {

• if (iter->desc_nr == nr) {
  

• 	rdev = iter;
  break;
  

• }
  

  }

• if (!rdev || rdev->desc_nr != nr) {

• if (!rdev) { pr_warn("%s: %d Could not find rdev with nr %d\n", __func__, __LINE__, nr); return; }

I guess we only need to check desc_nr since rdev should always be valid , and IMO the fix tag is not necessary.

@@ -9800,7 +9800,7 @@ void md_reload_sb(struct mddev *mddev, int nr)                         break;         }

-       if (!rdev || rdev->desc_nr != nr) { +       if (rdev->desc_nr != nr) {

Thanks, Guoqing