linux-kernel - Re: [PATCH] procfs: block chmod on /proc/thread-self/comm

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Date:   Thu, 13 Jul 2023 15:22:24 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Thomas Weißschuh <thomas@...ch.de>
Cc:     Aleksa Sarai <cyphar@...har.com>, Willy Tarreau <w@....eu>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <dchinner@...hat.com>,
        xu xin <cgel.zte@...il.com>, Al Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...kernel.io>,
        Zhihao Cheng <chengzhihao1@...wei.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Janis Danisevskis <jdanis@...gle.com>,
        Kees Cook <keescook@...omium.org>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] procfs: block chmod on /proc/thread-self/comm

> > diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> > index 486334981e60..08f0969208eb 100644
> > --- a/tools/testing/selftests/nolibc/nolibc-test.c
> > +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> > @@ -580,6 +580,10 @@ int run_syscall(int min, int max)
> >  		CASE_TEST(chmod_net);         EXPECT_SYSZR(proc, chmod("/proc/self/net", 0555)); break;
> >  		CASE_TEST(chmod_self);        EXPECT_SYSER(proc, chmod("/proc/self", 0555), -1, EPERM); break;
> >  		CASE_TEST(chown_self);        EXPECT_SYSER(proc, chown("/proc/self", 0, 0), -1, EPERM); break;
> > +		CASE_TEST(chmod_self_comm);   EXPECT_SYSER(proc, chmod("/proc/self/comm", 0777), -1, EPERM); break;
> > +		CASE_TEST(chmod_tid_comm);    EXPECT_SYSER(proc, chmod("/proc/thread-self/comm", 0777), -1, EPERM); break;
> > +		CASE_TEST(chmod_self_environ);EXPECT_SYSER(proc, chmod("/proc/self/environ", 0777), -1, EPERM); break;
> > +		CASE_TEST(chmod_tid_environ); EXPECT_SYSER(proc, chmod("/proc/thread-self/environ", 0777), -1, EPERM); break;

> 
> I'm not a big fan of this, it abuses the nolibc testsuite to test core
> kernel functionality.

Yes, this should be dropped.
We need a minimal patch to fix this. This just makes backporting harder
and any test doesn't need to be backported.