CVE-2026-68179

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

misc: nsm: only unlock nsm_dev on post-lock error paths

nsmdevioctl() jumps to the common out label even when the initial copyfromuser() fails before nsm->lock has been taken. The error path then blindly unlocks a mutex that was never acquired.

This issue was found by our static analysis tool and then manually reviewed against the current tree.

The grounded PoC kept the miscdevice ioctl entry and the pre-lock copyfromuser(&raw, argp, IOCSIZE(cmd)) failure path by issuing NSMIOCTLRAW with an invalid user pointer. That failure reaches the shared out label before mutex_lock(&nsm->lock). Lockdep reported:

WARNING: bad unlock balance detected! exploit/193 is trying to release lock (&globalnsm.lock) at: nsmdevioctl+0x5f/0xcf [vulnmsv] but there are no more locks to release! no locks held by exploit/193.

Return immediately on the pre-lock copyfromuser() failure and keep the common unlock label for the post-lock paths only.