mm: Create utility function for accessing a tasks commandline value

introduce get_cmdline() for retreiving the value of a processes
proc/self/cmdline value.

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>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/mm/util.c b/mm/util.c
index 808f375648e7..43b44199c5e3 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -413,6 +413,54 @@ unsigned long vm_commit_limit(void)
                 * sysctl_overcommit_ratio / 100) + total_swap_pages;
 }
 
+/**
+ * get_cmdline() - copy the cmdline value to a buffer.
+ * @task:     the task whose cmdline value to copy.
+ * @buffer:   the buffer to copy to.
+ * @buflen:   the length of the buffer. Larger cmdline values are truncated
+ *            to this length.
+ * Returns the size of the cmdline field copied. Note that the copy does
+ * not guarantee an ending NULL byte.
+ */
+int get_cmdline(struct task_struct *task, char *buffer, int buflen)
+{
+        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 > buflen)
+                len = buflen;
+
+        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 < buflen) {
+                len = strnlen(buffer, res);
+                if (len < res) {
+                        res = len;
+                } else {
+                        len = mm->env_end - mm->env_start;
+                        if (len > buflen - res)
+                                len = buflen - res;
+                        res += access_process_vm(task, mm->env_start,
+                                                 buffer+res, len, 0);
+                        res = strnlen(buffer, res);
+                }
+        }
+out_mm:
+        mmput(mm);
+out:
+        return res;
+}
 
 /* Tracepoints definitions. */
 EXPORT_TRACEPOINT_SYMBOL(kmalloc);