Re: [PATCH] proc: Track /proc/$pid/attr/ opener mm_struct

From: Greg KH <gregkh@linuxfoundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	youling 257 <youling257@gmail.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Andrea Righi <andrea.righi@canonical.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	regressions@lists.linux.dev,
	LSM List <linux-security-module@vger.kernel.org>,
	Paul Moore <paul@paul-moore.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>,
	SElinux list <selinux@vger.kernel.org>
Subject: Re: [PATCH] proc: Track /proc/$pid/attr/ opener mm_struct
Date: Wed, 16 Jun 2021 07:56:06 +0200	[thread overview]
Message-ID: <YMmSdqnspAXG1CyT@kroah.com> (raw)
In-Reply-To: <202106151449.816D7DA682@keescook>

On Tue, Jun 15, 2021 at 02:50:39PM -0700, Kees Cook wrote:
> On Tue, Jun 15, 2021 at 11:19:04AM -0700, Linus Torvalds wrote:
> > On Mon, Jun 14, 2021 at 6:55 PM youling 257 <youling257@gmail.com> wrote:
> > >
> > > if try to find problem on userspace, i used linux 5.13rc6 on old
> > > android 7 cm14.1, not aosp android 11.
> > > http://git.osdn.net/view?p=android-x86/system-core.git;a=blob;f=init/service.cpp;h=a5334f447fc2fc34453d2f6a37523bedccadc690;hb=refs/heads/cm-14.1-x86#l457
> > >
> > >  457         if (!seclabel_.empty()) {
> > >  458             if (setexeccon(seclabel_.c_str()) < 0) {
> > >  459                 ERROR("cannot setexeccon('%s'): %s\n",
> > >  460                       seclabel_.c_str(), strerror(errno));
> > >  461                 _exit(127);
> > >  462             }
> > >  463         }
> > 
> > I have no idea where the cm14.1 libraries are. Does anybody know where
> > the matching source code for setexeccon() would be?
> > 
> > For me - obviously not on cm14.1 - all "setexeccon()" does is
> > 
> >    n = openat(AT_FDCWD, "/proc/thread-self/attr/exec", O_RDWR|O_CLOEXEC)
> >    write(n, string, len)
> >    close(n)
> > 
> > and if that fails, it would seem to indicate that proc_mem_open()
> > failed. Which would be mm_access() failing. But I don't see how that
> > can be the case, because mm_access() explicitly allows "mm ==
> > current->mm" (which the above clearly should be).
> 
> Yeah, that was what I saw too.
> 
> > youling, can you double-check with the current -git tree? But as far
> > as I can tell, my minimal patch is exactly the same as Kees' patch
> > (just smaller and simpler).
> 
> FWIW, for that patch:
> 
> Acked-by: Kees Cook <keescook@chromium.org>
> Cc: stable@vger.kernel.org

Thanks, I'll go pick it up now.

greg k-h