Description

In the Linux kernel, the following vulnerability has been resolved: rtmutex: Use waiter::task instead of current in remove_waiter() remove_waiter() is used by the slowlock paths, but it is also used for proxy-lock rollback in rt_mutex_start_proxy_lock() when invoked from futex_requeue(). In the latter case waiter::task is not current, but remove_waiter() operates on current for the dequeue operation. That results in several problems: 1) the rbtree dequeue happens without waiter::task::pi_lock being held 2) the waiter task's pi_blocked_on state is not cleared, which leaves a dangling pointer primed for UAF around. 3) rt_mutex_adjust_prio_chain() operates on the wrong top priority waiter task Use waiter::task instead of current in all related operations in remove_waiter() to cure those problems. [ tglx: Fixup rt_mutex_adjust_prio_chain(), add a comment and amend the changelog ]

References 6

• git.kernel.org https://git.kernel.org/stable/c/3bfdc63936dd4773109b7b8c280c0f3b5ae7d349
• git.kernel.org https://git.kernel.org/stable/c/3fb7394a837740770f0d6b4b30567e60786a63f2
• git.kernel.org https://git.kernel.org/stable/c/6d52dfcb2a5db86e346cf51f8fcf2071b8085166
• git.kernel.org https://git.kernel.org/stable/c/88614876370aac8ad1050ad785a4c095ba17ac11
• git.kernel.org https://git.kernel.org/stable/c/8a1fc8d698ac5e5916e3082a0f74450d71f9611f
• git.kernel.org https://git.kernel.org/stable/c/d8cce4773c2b23d819baf5abedc62f7b430e8745

Remediation