CVE-2026-72345: net/mlx5: LAG, Fix off-by-one in single-FDB error rollback

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: LAG, Fix off-by-one in single-FDB error rollback

On failure at index i, the reverse cleanup loop in mlx5lagcreatesinglefdb() starts from i, so the failed index itself is rolled back. That can operate on uninitialized state or double-tear-down a rule the addone path already self-rolled-back.

Start the rollback from i - 1 so only successfully-installed entries are undone.