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 [off-list ref] wrote:

quoted

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.

[...]

quoted

+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")`.)

quoted

+       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...

[...]

quoted

+       /* 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.