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

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Date:   Thu, 13 Jul 2023 16:12:43 +0200
From:   Thomas Weißschuh <thomas@...ch.de>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     Christian Brauner <brauner@...nel.org>, 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

On 2023-07-14 00:00:51+1000, Aleksa Sarai wrote:
> On 2023-07-13, Christian Brauner <brauner@...nel.org> wrote:
> > > > 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.
> 
> Alright, I'll drop it in v2 (though I'm not sure why there are tests for
> /proc/self and /proc/self/net then).

To test the functionality of the implementations of chown() and chmod()
in nolibc. procfs is used used as a test fixture to provide diverse file
and directories that are (nearly) always available.

The system under test is nolibc, not the kernel itself.

Thomas