On Tue, 31 Oct 2017, tip-bot for Peter Zijlstra wrote: > Commit-ID: d5f6ac33189af48a0dc011190af5144947a30a76 > Gitweb: > https://git.kernel.org/tip/d5f6ac33189af48a0dc011190af5144947a30a76 > Author: Peter Zijlstra <[email protected]> > AuthorDate: Tue, 31 Oct 2017 11:18:53 +0100 > Committer: Ingo Molnar <[email protected]> > CommitDate: Tue, 31 Oct 2017 11:54:52 +0100 > > futex: Fix more put_pi_state() vs. exit_pi_state_list() races > > Dmitry (through syzbot) reported being able to trigger the WARN in > get_pi_state() and a use-after-free on: > > raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); > > Both are due to this race: > > exit_pi_state_list() put_pi_state() > > lock(&curr->pi_lock) > while() { > pi_state = list_first_entry(head); > hb = hash_futex(&pi_state->key); > unlock(&curr->pi_lock); > > > dec_and_test(&pi_state->refcount); > > lock(&hb->lock) > lock(&pi_state->pi_mutex.wait_lock) // uaf if pi_state free'd > lock(&curr->pi_lock); > > .... > > unlock(&curr->pi_lock); > get_pi_state(); // WARN; refcount==0 > > The problem is we take the reference count too late, and don't allow it > being 0. Fix it by using inc_not_zero() and simply retrying the loop > when we fail to get a refcount. In that case put_pi_state() should > remove the entry from the list. > > Reported-by: Dmitry Vyukov <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Cc: Gratian Crisan <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: [email protected] > Cc: syzbot > <bot+2af19c9e1ffe4d4ee1d16c56ae7580feaee75...@syzkaller.appspotmail.com> > Cc: [email protected] > Fixes: c74aef2d06a9 ("futex: Fix pi_state->owner serialization") > Link: > http://lkml.kernel.org/r/[email protected] > Signed-off-by: Ingo Molnar <[email protected]>
That lacks a stable tag. Other than that a late: Reviewed-by: Thomas Gleixner <[email protected]>
