proc: Update get proc_pid_cmdline() to use mm.h helpers

Re-factor proc_pid_cmdline() to use get_cmdline() helper
from mm.h.

Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Richard Guy Briggs <rgb@redhat.com>

Signed-off-by: William Roberts <wroberts@tresys.com>
Acked-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

fs/proc/base.c

@@ -200,41 +200,9 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
 	return result;
 }
 
-static int proc_pid_cmdline(struct task_struct *task, char * buffer)
+static int proc_pid_cmdline(struct task_struct *task, char *buffer)
 {
-	int res = 0;
-	unsigned int len;
-	struct mm_struct *mm = get_task_mm(task);
-	if (!mm)
-		goto out;
-	if (!mm->arg_end)
-		goto out_mm;	/* Shh! No looking before we're done */
-
- 	len = mm->arg_end - mm->arg_start;
-
-	if (len > PAGE_SIZE)
-		len = PAGE_SIZE;
-
-	res = access_process_vm(task, mm->arg_start, buffer, len, 0);
-
-	// If the nul at the end of args has been overwritten, then
-	// assume application is using setproctitle(3).
-	if (res > 0 && buffer[res-1] != '\0' && len < PAGE_SIZE) {
-		len = strnlen(buffer, res);
-		if (len < res) {
-		    res = len;
-		} else {
-			len = mm->env_end - mm->env_start;
-			if (len > PAGE_SIZE - res)
-				len = PAGE_SIZE - res;
-			res += access_process_vm(task, mm->env_start, buffer+res, len, 0);
-			res = strnlen(buffer, res);
-		}
-	}
-out_mm:
-	mmput(mm);
-out:
-	return res;
+	return get_cmdline(task, buffer, PAGE_SIZE);
 }
 
 static int proc_pid_auxv(struct task_struct *task, char *buffer)