From: Michal Hocko <mhocko@kernel.org>
To: Yizhuo <yzhai003@ucr.edu>
Cc: csong@cs.ucr.edu, zhiyunq@cs.ucr.edu,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/memcg: return value of the function mem_cgroup_from_css() is not checked
Date: Thu, 22 Aug 2019 09:05:50 +0200 [thread overview]
Message-ID: <20190822070550.GA12785@dhcp22.suse.cz> (raw)
In-Reply-To: <20190822062210.18649-1-yzhai003@ucr.edu>
On Wed 21-08-19 23:22:09, Yizhuo wrote:
> Inside function mem_cgroup_wb_domain(), the pointer memcg
> could be NULL via mem_cgroup_from_css(). However, this pointer is
> not checked and directly dereferenced in the if statement,
> which is potentially unsafe.
Could you describe circumstances when this would happen? The code is
this way for 5 years without any issues. Are we just lucky or something
has changed recently to make this happen?
> Signed-off-by: Yizhuo <yzhai003@ucr.edu>
> ---
> mm/memcontrol.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 661f046ad318..bd84bdaed3b0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3665,7 +3665,7 @@ struct wb_domain *mem_cgroup_wb_domain(struct bdi_writeback *wb)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
>
> - if (!memcg->css.parent)
> + if (!memcg || !memcg->css.parent)
> return NULL;
>
> return &memcg->cgwb_domain;
> --
> 2.17.1
>
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-08-22 7:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 6:22 [PATCH] mm/memcg: return value of the function mem_cgroup_from_css() is not checked Yizhuo
2019-08-22 7:05 ` Michal Hocko [this message]
[not found] ` <CABvMjLRCt4gC3GKzBehGppxfyMOb6OGQwW-6Yu_+MbMp5tN3tg@mail.gmail.com>
2019-08-22 20:12 ` Michal Hocko
2019-08-30 22:27 ` Yizhuo Zhai
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=20190822070550.GA12785@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=cgroups@vger.kernel.org \
--cc=csong@cs.ucr.edu \
--cc=hannes@cmpxchg.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=vdavydov.dev@gmail.com \
--cc=yzhai003@ucr.edu \
--cc=zhiyunq@cs.ucr.edu \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).