From: Jiri Olsa <jolsa@redhat.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Michael Petlan <mpetlan@redhat.com>,
Wade Mealing <wmealing@redhat.com>
Subject: Re: [PATCH] perf: Fix race in perf_mmap_close function
Date: Thu, 10 Sep 2020 16:47:44 +0200 [thread overview]
Message-ID: <20200910144744.GA1663813@krava> (raw)
In-Reply-To: <CAM9d7cjqq8+wcZWJ77oONKXu-FsaT_YvRxzaGbRT8PjLOw-AkQ@mail.gmail.com>
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 <jolsa@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
jirka
next prev parent reply other threads:[~2020-09-10 20:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 10:41 [PATCH] perf: Fix race in perf_mmap_close function Jiri Olsa
2020-09-10 13:48 ` Namhyung Kim
2020-09-10 14:47 ` Jiri Olsa [this message]
2020-09-11 3:05 ` Namhyung Kim
2020-09-11 7:49 ` Jiri Olsa
2020-09-14 12:48 ` Namhyung Kim
2020-09-14 20:59 ` Jiri Olsa
2020-09-15 15:35 ` Michael Petlan
2020-09-16 11:53 ` [PATCHv2] " Jiri Olsa
2020-09-16 13:54 ` peterz
2020-09-16 14:38 ` Jiri Olsa
2020-09-16 14:05 ` peterz
2020-10-12 11:45 ` [tip: perf/core] perf/core: Fix race in the perf_mmap_close() function tip-bot2 for Jiri Olsa
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