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From:   youling 257 <youling257@gmail.com>
Date:   Wed, 16 Jun 2021 13:15:25 +0800
Message-ID: <CAOzgRdazu1TjP0+2ttnrQq5JzymcPog0z52YvsUCZAnFKvufDQ@mail.gmail.com>
Subject: Re: [PATCH] proc: Track /proc/$pid/attr/ opener mm_struct
To:     Linus Torvalds <torvalds@linux-foundation.org>
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>
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I test "proc: only require mm_struct for writing" fixed my cm14.1 problem.

2021-06-16 2:19 GMT+08:00, Linus Torvalds <torvalds@linux-foundation.org>:
> 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
>