linux-kernel - Re: [PATCH v2 2/2] pidfd: add tests for NSpid info in fdinfo

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Message-ID: <20191011170848.nbfxzzl5qckkshkr@wittgenstein>
Date:   Fri, 11 Oct 2019 19:08:50 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Christian Kellner <ckellner@...hat.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Christian Kellner <christian@...lner.me>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] pidfd: add tests for NSpid info in fdinfo

On Fri, Oct 11, 2019 at 05:09:29PM +0200, Jann Horn wrote:
> On Wed, Oct 9, 2019 at 6:10 PM Christian Kellner <ckellner@...hat.com> wrote:
> > Add tests that check that if pid namespaces are configured the fdinfo
> > file of a pidfd contains an NSpid: entry containing the process id
> > in the current and additionally all nested namespaces.
> [...]
> > +static int compare_fdinfo_nspid(int pidfd, char *expect, size_t len)
> > +{
> > +       char path[512];
> > +       FILE *f;
> > +       size_t n = 0;
> > +       ssize_t k;
> > +       char *line = NULL;
> > +       int r = -1;
> > +
> > +       snprintf(path, sizeof(path), "/proc/self/fdinfo/%d", pidfd);
> 
> (Maybe at some point the selftests code should add some more concise
> alternative to snprintf() calls on separate lines. A macro or
> something like that so that you can write stuff like `f =
> fopen(tprintf("/proc/self/fdinfo/%d", pidfd), "re")`.)
> 
> > +       f = fopen(path, "re");
> > +       if (!f)
> > +               return -1;
> > +
> > +       while ((k = getline(&line, &n, f)) != -1) {
> > +               if (strncmp(line, "NSpid:", 6))
> > +                       continue;
> > +
> > +               line[k - 1] = '\0';
> > +               ksft_print_msg("Child: fdinfo NSpid line: '%s'.\n", line);
> > +               r = strncmp(line + 6, expect, len);
> 
> Wouldn't it be better to get rid of the nullbyte assignment and change
> the strncmp() into a strcmp() here...
> 
> [...]
> > +       /* The child will have pid 1 in the new pid namespace,
> > +        * so the line must be 'NSPid:\t<pid>\t1'
> > +        */
> > +       n = snprintf(expect, sizeof(expect), "\t%d\t%d", pid, 1);
> 
> ... and add a "\n" to the format string? It's shorter and doesn't
> silently ignore it if the line doesn't end at that point.

Also, what Christian just told me and what I wanted to suggest is that
we add tests for sending around pidfds and reading fdinfo too.