LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Namhyung Kim <namhyung@kernel.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: 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 22:48:02 +0900
Message-ID: <CAM9d7cjqq8+wcZWJ77oONKXu-FsaT_YvRxzaGbRT8PjLOw-AkQ@mail.gmail.com> (raw)
In-Reply-To: <20200910104153.1672460-1-jolsa@kernel.org>

On Thu, Sep 10, 2020 at 7:42 PM Jiri Olsa <jolsa@kernel.org> wrote:
>
> There's a possible race in perf_mmap_close when checking ring buffer's
> mmap_count refcount value. The problem is that the mmap_count check is
> not atomic because we call atomic_dec and atomic_read separately.
>
>   perf_mmap_close:
>   ...
>    atomic_dec(&rb->mmap_count);
>    ...
>    if (atomic_read(&rb->mmap_count))
>       goto out_put;
>
>    <ring buffer detach>
>    free_uid
>
> out_put:
>   ring_buffer_put(rb); /* could be last */
>
> The race can happen when we have two (or more) events sharing same ring
> buffer and they go through atomic_dec and then they both see 0 as refcount
> value later in atomic_read. Then both will go on and execute code which
> is meant to be run just once.
>
> The code that detaches ring buffer is probably fine to be executed more
> than once, but the problem is in calling free_uid, which will later on
> demonstrate in related crashes and refcount warnings, like:
>
>   refcount_t: addition on 0; use-after-free.
>   ...
>   RIP: 0010:refcount_warn_saturate+0x6d/0xf
>   ...
>   Call Trace:
>   prepare_creds+0x190/0x1e0
>   copy_creds+0x35/0x172
>   copy_process+0x471/0x1a80
>   _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..

Thanks
Namhyung

>
> @@ -5912,7 +5910,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
>         mutex_unlock(&event->mmap_mutex);
>
>         /* If there's still other mmap()s of this buffer, we're done. */
> -       if (atomic_read(&rb->mmap_count))
> +       if (!atomic_dec_and_test(&rb->mmap_count))
>                 goto out_put;
>
>         /*
> --
> 2.26.2
>

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-10 10:41 Jiri Olsa
2020-09-10 13:48 ` Namhyung Kim [this message]
2020-09-10 14:47   ` Jiri Olsa
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAM9d7cjqq8+wcZWJ77oONKXu-FsaT_YvRxzaGbRT8PjLOw-AkQ@mail.gmail.com \
    --to=namhyung@kernel.org \
    --cc=a.p.zijlstra@chello.nl \
    --cc=acme@kernel.org \
    --cc=alexander.shishkin@linux.intel.com \
    --cc=jolsa@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=mpetlan@redhat.com \
    --cc=wmealing@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git