net: kcm: Fix race condition in kcm_unattach()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: kcm: Fix race condition in kcm_unattach() syzbot found a race condition when kcm_unattach(psock) and kcm_release(kcm) are executed at the same time. kcm_unattach() is missing a check of the flag kcm->tx_stopped before calling queue_work(). If the kcm has a reserved psock, kcm_unattach() might get executed between cancel_work_sync() and unreserve_psock() in kcm_release(), requeuing kcm->tx_work right before kcm gets freed in kcm_done(). Remove kcm->tx_stopped and replace it by the less error-prone disable_work_sync().

References

• https://git.kernel.org/stable/c/c0bffbc92a1ca3960fb9cdb8e9f75a68468eb308
• https://git.kernel.org/stable/c/7275dc3bb8f91b23125ff3f47b6529935cf46152
• https://git.kernel.org/stable/c/798733ee5d5788b12e8a52db1519abc17e826f69
• https://git.kernel.org/stable/c/52565a935213cd6a8662ddb8efe5b4219343a25d