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

On Tue, Jun 15, 2021 at 11:19:04AM -0700, Linus Torvalds wrote:

On Mon, Jun 14, 2021 at 6:55 PM youling 257 [off-list ref] wrote:

quoted

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 <redacted>
Cc: stable@vger.kernel.org

Kees, do you see anything?

No, I haven't been able to reproduce the failure. :(

-- 
Kees Cook