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

From: Greg KH
Date: Wed Jun 16 2021 - 01:56:14 EST


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@xxxxxxxxx> 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@xxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

Thanks, I'll go pick it up now.

greg k-h