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@vger.kernel.org Fixes: 70bcecdb1534 ("md-cluster: Improve md_reload_sb to be less error prone") Signed-off-by: Xiaomeng Tong xiam0nd.tong@gmail.com ---

changes from v2: - fix typo (Song Liu)

changes from v1: - rephrase the subject (Guoqing Jiang)

v2:https://lore.kernel.org/lkml/20220328080559.25984-1-xiam0nd.tong@gmail.com/ v1:https://lore.kernel.org/lkml/20220327080111.12028-1-xiam0nd.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; }