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

[Jann Horn]

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