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linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev Subject: Re: [PATCH 11/39] selinux: reject writable opens of policy file, drop mmap shared/write check Message-ID: References: <20260908-b4-mmap-prepare-vma-flag-sanify-v1-0-dacf19cce22b@kernel.org> <20260908-b4-mmap-prepare-vma-flag-sanify-v1-11-dacf19cce22b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AAECE1C0003 X-Stat-Signature: hnkb9j8xmusrs7i37d4k6kw8p7jto64s X-Rspam-User: X-HE-Tag: 1789121627-832755 X-HE-Meta: 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8n34lp9K3/NGNf5rQJdcbs8yMFNmbJPDUn2aeWbmsRqoUz9PT/coXFf7Yw+26d8R1yravw0bvBa5hE9WXBMq6KE2S631cvRE2gD/q7IrKnEU9GuV15IOtwtIzjLRY60irHymAx231zeICLrvxm6AYyCpgcM+zDaHUuy+bzixRC6Rvu/FxSiRYwskCCv7O+GwUgtMsz/xE8XclJHr10QlTZOyt6qxNIjw+0/tzPN1zFtmkDhydkmlnm8aT0iTgWQzqvic5WdRGIJVUA+K5pRq5+XKy/1XijpgcSNK8ho6tzNYKMdtGCcHcnQricOCuYR6d2VcCeujwLDwlfhgCJTrPDpigc82vebdMdxwa7K6WQ3SlESXj39MnN Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 08, 2026 at 10:22:20PM +0200, Jann Horn wrote: > On Tue, Sep 8, 2026 at 10:07 PM Lorenzo Stoakes (ARM) wrote: > > The policy file has no write method and is exposed read-only (S_IRUGO in > > selinux_files[]), yet sel_open_policy() performs no open mode check, so a > > CAP_DAC_OVERRIDE caller can open it O_RDWR. Reject FMODE_WRITE at open, as > > kernfs does. > > > > The file can then never be mapped with FMODE_WRITE, so do_mmap() always > > clears VM_MAYWRITE and VM_SHARED for MAP_SHARED mappings and the VM_SHARED > > check in sel_mmap_policy() cannot be reached. Remove it. > > You should also be able to remove the sel_mmap_policy_ops.page_mkwrite > handler, which is only for shared-writable faults, right? Yeah I think you're right, though I wonder if it's a bit out of scope for this change as it's focused on removing a VMA_MAYWRITE_BIT clearance for a non-kernel-owned VMA. So maybe one for a follow up? > > > This also stops sel_mmap_policy() clearing VM_MAYWRITE on a mapping that is > > neither a PFN map nor a mixed map, ahead of the core enforcing that only > > such mappings may do so. > > > > Signed-off-by: Lorenzo Stoakes (ARM) > > Reviewed-by: Jann Horn Thanks! -- Cheers, Lorenzo