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Subject[PATCH] md: md2: fix an incorrect NULL check on list iterator
Date
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")
Signed-off-by: Xiaomeng Tong <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;
}
--
2.17.1
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