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

memcg: make the v1 soft limit knob inert

The v1 soft limit has been deprecated since v6.12 and nobody has reported depending on it. Start the removal by decoupling the interface from the implementation: keep memory.soft limit in bytes, but ignore writes to it and always report the maximum value on read similar to what memory.kmem.limit in bytes already does.

Writes are still parsed, so malformed input keeps returning -EINVAL. The knob now also behaves the same everywhere: it used to return -EOPNOTSUPP on PREEMPT RT, where soft limit reclaim has always been disabled.

This also fixes the syzbot report linked below. Soft limit reclaim is the only caller that runs shrink lruvec() from kswapd against a specific memcg, so it is the only way to reach lru gen shrink lruvec() and in turn set mm walk(), which warns when called from kswapd.