On Fri, Oct 08, 2021 at 04:55:04PM -0700, Kees Cook wrote:
> This makes sure that wchan contains a sensible symbol when a process is
> blocked.
> Specifically this calls the sleep() syscall, and expects the
> architecture to have called schedule() from a function that has "sleep"
> somewhere in its name.
This exposes internal kernel symbol to userspace.
Why would want to test that?
Doing s/sleep/SLEEP/g doesn't change kernel but now the test is broken.
> For example, on the architectures I tested
> (x86_64, arm64, arm, mips, and powerpc) this is "hrtimer_nanosleep":
> +/*
> + * Make sure that wchan returns a reasonable symbol when blocked.
> + */
Test should be "contains C identifier" then?
> +int main(void)
> +{
> + char buf[64];
> + pid_t child;
> + int sync[2], fd;
> +
> + if (pipe(sync) < 0)
> + perror_exit("pipe");
> +
> + child = fork();
> + if (child < 0)
> + perror_exit("fork");
> + if (child == 0) {
> + /* Child */
> + if (close(sync[0]) < 0)
> + perror_exit("child close sync[0]");
> + if (close(sync[1]) < 0)
> + perror_exit("child close sync[1]");
Redundant close().
> + sleep(10);
> + _exit(0);
> + }
> + /* Parent */
> + if (close(sync[1]) < 0)
> + perror_exit("parent close sync[1]");
Redundant close().
> + if (read(sync[0], buf, 1) != 0)
> + perror_exit("parent read sync[0]");
Racy if child is scheduled out after first close in the child.
> + snprintf(buf, sizeof(buf), "/proc/%d/wchan", child);
> + fd = open(buf, O_RDONLY);
> + if (fd < 0) {
> + if (errno == ENOENT)
> + return 4;
> + perror_exit(buf);
> + }
> +
> + memset(buf, 0, sizeof(buf));
> + if (read(fd, buf, sizeof(buf) - 1) < 1)
> + perror_exit(buf);
> + if (strstr(buf, "sleep") == NULL) {
> + fprintf(stderr, "FAIL: did not find 'sleep' in wchan '%s'\n", buf);
> + return 1;
> + }
> + printf("ok: found 'sleep' in wchan '%s'\n", buf);
> +
> + if (kill(child, SIGKILL) < 0)
> + perror_exit("kill");
> + if (waitpid(child, NULL, 0) != child) {
> + fprintf(stderr, "waitpid: got the wrong child!?\n");
> + return 1;
> + }
> +
> + return 0;
> +}
