Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after being freed

From: Yang Shi <shy828301@gmail.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>, Michal Hocko <mhocko@suse.com>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
	Minchan Kim <minchan@kernel.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Andrea Arcangeli <aarcange@redhat.com>,
	brauner@kernel.org, christian@brauner.io,
	Christoph Hellwig <hch@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Jann Horn <jannh@google.com>, Shakeel Butt <shakeelb@google.com>,
	luto@kernel.org, christian.brauner@ubuntu.com,
	fweimer@redhat.com, jengelh@inai.de, timmurray@google.com,
	Linux MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	kernel-team@android.com,
	syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com
Subject: Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after being freed
Date: Tue, 15 Feb 2022 12:42:59 -0800	[thread overview]
Message-ID: <CAHbLzkoeCP-ONBNsDB-y63chxWCZejeQKXg6zc2AAQWCixjxQA@mail.gmail.com> (raw)
In-Reply-To: <20220215201922.1908156-1-surenb@google.com>

On Tue, Feb 15, 2022 at 12:19 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> After exit_mmap frees all vmas in the mm, mm->mmap needs to be reset,
> otherwise it points to a vma that was freed and when reused leads to
> a use-after-free bug.
>
> Reported-by: syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Looks good to me. Reviewed-by: Yang Shi <shy828301@gmail.com>

> ---
>  mm/mmap.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 1e8fdb0b51ed..d445c1b9d606 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm)
>                 vma = remove_vma(vma);
>                 cond_resched();
>         }
> +       mm->mmap = NULL;
>         mmap_write_unlock(mm);
>         vm_unacct_memory(nr_accounted);
>  }
> --
> 2.35.1.265.g69c8d7142f-goog
>