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

From: Jann Horn <jannh@google.com>
To: Christian Kellner <ckellner@redhat.com>
Cc: kernel list <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Christian Kellner <christian@kellner.me>,
	Christian Brauner <christian@brauner.io>,
	Shuah Khan <shuah@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>,
	Roman Gushchin <guro@fb.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"Dmitry V. Levin" <ldv@altlinux.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] pidfd: add tests for NSpid info in fdinfo
Date: Fri, 11 Oct 2019 17:09:29 +0200	[thread overview]
Message-ID: <CAG48ez0MyiTKO2MpNVQqavoTKo7FZXYAyohx1JTR=M9Uw=QJWQ@mail.gmail.com> (raw)
In-Reply-To: <20191009160532.20674-2-ckellner@redhat.com>

On Wed, Oct 9, 2019 at 6:10 PM Christian Kellner <ckellner@redhat.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.