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Donenfeld" , Alexander Viro , Christian Brauner , Jan Kara , Pavel Emelyanov , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 2/3] userfaultfd: prevent unregistering VMAs through a different userfaultfd Message-ID: References: <20250603-uffd-fixes-v1-0-9c638c73f047@columbia.edu> <20250603-uffd-fixes-v1-2-9c638c73f047@columbia.edu> <84cf5418-42e9-4ec5-bd87-17ba91995c47@redhat.com> <0a1dab1c-80d2-436f-857f-734d95939aec@redhat.com> MIME-Version: 1.0 In-Reply-To: <0a1dab1c-80d2-436f-857f-734d95939aec@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: c5SORq3yRZzX46MNeQw5DFJokH57s6nX5GoCs9xeOuc_1749215032 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A43E540017 X-Stat-Signature: 8chg334m88rwci1hxhzq4y9bo11rph8g X-Rspam-User: X-HE-Tag: 1749215036-901984 X-HE-Meta: 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 OstAKcGd q/ZzSoZADF1I8mDvdrQgCaw1MebtS9t7rtfLlLI9ezp0AeETSAAhr+csHo21KvDg1AIkBzkAqFNLeOO75Q2jewPAObfGJxleD1+KXBlrtc42RvWtCQO9fGNbXupy6j54QrzyCzNC3VZ8LScIhI2m0WEA/yobFSo/YjDqUA11bxdAyJfRRXWwmEP91W+IH/KDMiBzo9uqmyl9urrhIxrxGkH9N8JURv2sPwAIDnO/DorOkxu7ussr3PLeEBMBrb2LpvRDlfZHU0A13ySSJBlsC5sukC8i7z1iyyObH5OlntHypsyt7FBb1U/uYppDxuyDKcEgpu7Y37wbNFAfcbw2ucFpDdmC1m9UTavoswknBWkonXU2J5BSeL6NsLQnP4NbDrROTVM8ZIj/OdgemL5a0L7wwZz3fopRdGtPjv60e6sUU5TPBgmACN8HCTA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 05, 2025 at 11:06:38PM +0200, David Hildenbrand wrote: > Not sure if relevant, but consider the following: > > an app being controlled by another process using userfaultfd. > > The app itself can "escape" uffd control of the other process by simply > creating a userfaultfd and unregistering VMAs. IMHO it's okay if it's intentional by the child. E.g., even after this patch, the child, if intentional, can also mmap() a new VMA on top of the uffd tracked region to stop being trapped by the parent. The parent might still get a UNMAP event if registered, but it'll not be able to track the new VMAs mapped. Thanks, -- Peter Xu