Hi Jiri, On Thu, Sep 10, 2020 at 11:50 PM Jiri Olsa <jo...@redhat.com> wrote: > > On Thu, Sep 10, 2020 at 10:48:02PM +0900, Namhyung Kim wrote: > > SNIP > > > > _do_fork+0x83/0x3a0 > > > __do_sys_wait4+0x83/0x90 > > > __do_sys_clone+0x85/0xa0 > > > do_syscall_64+0x5b/0x1e0 > > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > > > Using atomic decrease and check instead of separated calls. > > > This fixes CVE-2020-14351. > > > > > > Signed-off-by: Jiri Olsa <jo...@kernel.org> > > > --- > > > kernel/events/core.c | 4 +--- > > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > > index 7ed5248f0445..29313cc54d9e 100644 > > > --- a/kernel/events/core.c > > > +++ b/kernel/events/core.c > > > @@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct > > > *vma) > > > mutex_unlock(&event->mmap_mutex); > > > } > > > > > > - atomic_dec(&rb->mmap_count); > > > - > > > if (!atomic_dec_and_mutex_lock(&event->mmap_count, > > > &event->mmap_mutex)) > > > goto out_put; > > > > But when it takes the goto, rb->mmap_count won't decrement anymore.. > > event->mmap_count is per event, so if we have have race in here, > 2 threads can go through with each event->mmap_count reaching zero
Maybe I'm missing something. But as far as I can see, perf_mmap_close() always decremented both rb->mmap_count and event->mmap_count. But with this change, it seems not decrement rb->mmap_count when event->mmap_count doesn't go to zero, right? Thanks Namhyung
