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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id e15sm1909094pfh.23.2020.05.14.08.45.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2020 08:45:14 -0700 (PDT) Date: Thu, 14 May 2020 08:45:13 -0700 From: Kees Cook To: Stephen Smalley Cc: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= , linux-kernel , Aleksa Sarai , Alexei Starovoitov , Al Viro , Andy Lutomirski , Christian Heimes , Daniel Borkmann , Deven Bowers , Eric Chiang , Florian Weimer , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Lakshmi Ramasubramanian , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= , Mimi Zohar , Philippe =?iso-8859-1?Q?Tr=E9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Steve Dower , Steve Grubb , Thibaut Sautereau , Vincent Strubel , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-integrity@vger.kernel.org, LSM List , Linux FS Devel Subject: Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC Message-ID: <202005140830.2475344F86@keescook> References: <20200505153156.925111-1-mic@digikod.net> <20200505153156.925111-4-mic@digikod.net> <202005131525.D08BFB3@keescook> <202005132002.91B8B63@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 14, 2020 at 08:22:01AM -0400, Stephen Smalley wrote: > On Wed, May 13, 2020 at 11:05 PM Kees Cook wrote: > > > > On Wed, May 13, 2020 at 04:27:39PM -0700, Kees Cook wrote: > > > Like, couldn't just the entire thing just be: > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > index a320371899cf..0ab18e19f5da 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -2849,6 +2849,13 @@ static int may_open(const struct path *path, int acc_mode, int flag) > > > break; > > > } > > > > > > + if (unlikely(mask & MAY_OPENEXEC)) { > > > + if (sysctl_omayexec_enforce & OMAYEXEC_ENFORCE_MOUNT && > > > + path_noexec(path)) > > > + return -EACCES; > > > + if (sysctl_omayexec_enforce & OMAYEXEC_ENFORCE_FILE) > > > + acc_mode |= MAY_EXEC; > > > + } > > > error = inode_permission(inode, MAY_OPEN | acc_mode); > > > if (error) > > > return error; > > > > > > > FYI, I've confirmed this now. Effectively with patch 2 dropped, patch 3 > > reduced to this plus the Kconfig and sysctl changes, the self tests > > pass. > > > > I think this makes things much cleaner and correct. > > I think that covers inode-based security modules but not path-based > ones (they don't implement the inode_permission hook). For those, I > would tentatively guess that we need to make sure FMODE_EXEC is set on > the open file and then they need to check for that in their file_open > hooks. I kept confusing myself about what order things happened in, so I made these handy notes about the call graph: openat2(dfd, char * filename, open_how) do_filp_open(dfd, filename, open_flags) path_openat(nameidata, open_flags, flags) do_open(nameidata, file, open_flags) may_open(path, acc_mode, open_flag) inode_permission(inode, MAY_OPEN | acc_mode) security_inode_permission(inode, acc_mode) vfs_open(path, file) do_dentry_open(file, path->dentry->d_inode, open) if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) ... security_file_open(f) open() So, it looks like adding FMODE_EXEC into f_flags in do_open() is needed in addition to injecting MAY_EXEC into acc_mode in do_open()? Hmmm -- Kees Cook