From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A85273CF1F0; Fri, 11 Sep 2026 10:16:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789121807; cv=none; b=iB1NN+Xle04CzXtYZV7Yrz51R90PYU9RFFF5qUBsYrwHcwZWPnKStc3sHfnBk+oewk2JJAXoOSsj7tiwExazvUs0D0gdOkJL3C3HuCFB6c/Bf+j47tqMX8OpNavVIRYw1EtAzqNABeLVtIPTXm9ZJaJaGvs+5+coISO+tBa7WjU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789121807; c=relaxed/simple; bh=vTsPXaHi8RAzBaWbL447Y7Wml4ZSeJ0BE4+oGF83XiM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VfULfKtT0eEwotwelT327Y+zHp8Xx8rUQ9pIKLl4J/4EQygHBBSYlbgOrVnN363ru4tOxiaB1w0T8fcxepr8zf/Fb738AONethY+9NM/OO4aWTW+C3iPQbXMdJ/kgEJ6/b3jJMMAcyKtnlYX8v3sIEarQHXPAHFKmZIVMBV0gQo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bAW41siy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bAW41siy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0B0E1F000FF; Fri, 11 Sep 2026 10:16:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789121805; bh=giLIDOVuGk3wU4sINvGbjDY5Co7tru0+JFiE0K9FPLI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=bAW41siy0jHTB1qfl3qn4gdNLwygOP92sxwRZ5j93bg2aVlvwhPZHWNQXCkbUnxC6 9zk3b5mbI7ab2hw7oNcaGXVKHnNx1qFzqMm5NsCPo7iMQTWRRa4ga4/FYZMgemnHMR LUWR9RDzd1jBIAPZg7P5yYAnVdcGzlswz7uYblSZrI8mgcWzefXPuZrclq/aRa18mg UXHtcfHYeWzL2TMktPNfUxYpL9byrk5pz2SSOJ+Hi6IFxR8hMDvGKPZB2iRfKGLL8X ZmrHB9kpMAfbsIpyQlYJu0jR9aIkQQcmQfumaGM+wf3Q1dTyf8WnZzhQjhpzxy2VYs gbIALJ3tDM5qQ== Date: Fri, 11 Sep 2026 11:16:14 +0100 From: "Lorenzo Stoakes (ARM)" To: Stephen Smalley Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , David Hildenbrand , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Greg Kroah-Hartman , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Paul Moore , Jaroslav Kysela , Takashi Iwai , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Doug Gilbert , "James E.J. Bottomley" , "Martin K. Petersen" , Jaya Kumar , Simona Vetter , Helge Deller , Sebastian Reichel , John Hubbard , Peter Xu , Masami Hiramatsu , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Rik van Riel , Harry Yoo , Juri Lelli , Vincent Guittot , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Arnd Bergmann , Muchun Song , Oscar Salvador , "Matthew Wilcox (Oracle)" , Jan Kara , Marc Zyngier , Oliver Upton , Catalin Marinas , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , "David S. Miller" , Andreas Larsson , Alexander Viro , Christian Brauner , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Johannes Weiner , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Xu Xin , Chengming Zhou , Michal Hocko , Miklos Szeredi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, 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> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Sep 10, 2026 at 02:11:18PM -0400, Stephen Smalley wrote: > On Tue, Sep 8, 2026 at 4:07 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. > > > > 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) > > We should likely do something similar for the other sel_open_*() and > sel_mmap_*() functions too. > In particular, truncation of the status file can bring down systemd > since it is mapped by libselinux. Yeah I think there's definitely more that can be done there. Though I think obviously that kind of stuff is better as a follow up as this patch is focused on eliminating a case where VMA_MAYWRITE_BIT is cleared incorrectly. > > Acked-by: Stephen Smalley Thanks! > > > --- > > security/selinux/selinuxfs.c | 11 +++-------- > > 1 file changed, 3 insertions(+), 8 deletions(-) > > > > diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c > > index c7d91476971c..545a6f89f9e7 100644 > > --- a/security/selinux/selinuxfs.c > > +++ b/security/selinux/selinuxfs.c > > @@ -340,6 +340,9 @@ static int sel_open_policy(struct inode *inode, struct file *filp) > > struct policy_load_memory *plm = NULL; > > int rc; > > > > + if (filp->f_mode & FMODE_WRITE) > > + return -EACCES; > > + > > rc = avc_has_perm(current_sid(), SECINITSID_SECURITY, > > SECCLASS_SECURITY, SECURITY__READ_POLICY, NULL); > > if (rc) > > @@ -424,14 +427,6 @@ static const struct vm_operations_struct sel_mmap_policy_ops = { > > > > static int sel_mmap_policy(struct file *filp, struct vm_area_struct *vma) > > { > > - if (vma->vm_flags & VM_SHARED) { > > - /* do not allow mprotect to make mapping writable */ > > - vm_flags_clear(vma, VM_MAYWRITE); > > - > > - if (vma->vm_flags & VM_WRITE) > > - return -EACCES; > > - } > > - > > vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP); > > vma->vm_ops = &sel_mmap_policy_ops; > > > > > > -- > > 2.55.0 > > -- Cheers, Lorenzo