From: Johannes Weiner <hannes@cmpxchg.org>
To: Tejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Jann Horn <jannh@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeelb@google.com>,
Muchun Song <songmuchun@bytedance.com>,
cgroups@vger.kernel.org
Subject: Re: [PATCH for-6.1-fixes] memcg: Fix possible use-after-free in memcg_write_event_control()
Date: Thu, 8 Dec 2022 15:36:34 +0100 [thread overview]
Message-ID: <Y5H2clPCac1gIE7I@cmpxchg.org> (raw)
In-Reply-To: <Y5FRm/cfcKPGzWwl@slm.duckdns.org>
On Wed, Dec 07, 2022 at 04:53:15PM -1000, Tejun Heo wrote:
> memcg_write_event_control() accesses the dentry->d_name of the specified
> control fd to route the write call. As a cgroup interface file can't be
> renamed, it's safe to access d_name as long as the specified file is a
> regular cgroup file. Also, as these cgroup interface files can't be removed
> before the directory, it's safe to access the parent too.
>
> Prior to 347c4a874710 ("memcg: remove cgroup_event->cft"), there was a call
> to __file_cft() which verified that the specified file is a regular cgroupfs
> file before further accesses. The cftype pointer returned from __file_cft()
> was no longer necessary and the commit inadvertently dropped the file type
> check with it allowing any file to slip through. With the invarients broken,
> the d_name and parent accesses can now race against renames and removals of
> arbitrary files and cause use-after-free's.
>
> Fix the bug by resurrecting the file type check in __file_cft(). Now that
> cgroupfs is implemented through kernfs, checking the file operations needs
> to go through a layer of indirection. Instead, let's check the superblock
> and dentry type.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Fixes: 347c4a874710 ("memcg: remove cgroup_event->cft")
> Cc: stable@vger.kernel.org # v3.14+
> Reported-by: Jann Horn <jannh@google.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
prev parent reply other threads:[~2022-12-08 14:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-08 2:53 Tejun Heo
2022-12-08 3:43 ` Roman Gushchin
2022-12-08 14:36 ` Johannes Weiner [this message]
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