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

From: Linus Torvalds <torvalds@linux-foundation.org>
To: youling 257 <youling257@gmail.com>
Cc: Kees Cook <keescook@chromium.org>,
	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: Tue, 15 Jun 2021 11:19:04 -0700	[thread overview]
Message-ID: <CAHk-=winAqy0sjgog9oEsjoBWOGJscFYEc3-=nvtzbyjTw_b+g@mail.gmail.com> (raw)
In-Reply-To: <CAOzgRdahaEjtk4jS5N=FQEDbsZVnB+-=xD+-WtV9zD9Tgbm0Hg@mail.gmail.com>

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).

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).

Kees, do you see anything?

           Linus