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

[Kees Cook]

On Tue, Jun 15, 2021 at 02:46:19AM +0800, youling 257 wrote:
> I test this patch cause "init: cannot setexeccon(u:r:ueventd:s0)
> operation not permitted.
> init ctrl_write_limited.

Thanks for testing!

This appears to come from here:
https://github.com/aosp-mirror/platform_system_core/blob/master/init/service.cpp#L242


In setexeccon(), I see (pid=0, attr="exec"):

        fd = openattr(pid, attr, O_RDWR | O_CLOEXEC);
...
                        ret = write(fd, context2, strlen(context2) + 1);
...
        close(fd);


and openattr() is doing:
...
                rc = asprintf(&path, "/proc/thread-self/attr/%s", attr);
                if (rc < 0)
                        return -1;
                fd = open(path, flags | O_CLOEXEC);
...

I'm not sure how the above could fail. (mm_access() always allows
introspection...)

The only way I can understand the check failing is if a process did:

open, exec, write

But setexeccon() is not doing anything between the open and the write...

I will keep looking...

-Kees

-- 
Kees Cook