uprobes: Change uprobe_copy_process() to dup return_instances

uprobe_copy_process() assumes that the new child doesn't need
->utask, it should be allocated by demand.

But this is not true if the forking task has the pending ret-
probes, the child should report them as well and thus it needs
the copy of parent's ->return_instances chain. Otherwise the
child crashes when it returns from the probed function.

Alternatively we could cleanup the child's stack, but this needs
per-arch changes and this is not what we want. At least systemtap
expects a .return in the child too.

Note: this change alone doesn't fix the problem, see the next
change.

Reported-by: Martin Cermak <mcermak@redhat.com>
Reported-by: David Smith <dsmith@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 7d12a45842a7..1c6cda68a555 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1366,12 +1366,55 @@ static struct uprobe_task *get_utask(void)
         return current->utask;
 }
 
+static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
+{
+        struct uprobe_task *n_utask;
+        struct return_instance **p, *o, *n;
+
+        n_utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
+        if (!n_utask)
+                return -ENOMEM;
+        t->utask = n_utask;
+
+        p = &n_utask->return_instances;
+        for (o = o_utask->return_instances; o; o = o->next) {
+                n = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
+                if (!n)
+                        return -ENOMEM;
+
+                *n = *o;
+                atomic_inc(&n->uprobe->ref);
+                n->next = NULL;
+
+                *p = n;
+                p = &n->next;
+                n_utask->depth++;
+        }
+
+        return 0;
+}
+
+static void uprobe_warn(struct task_struct *t, const char *msg)
+{
+        pr_warn("uprobe: %s:%d failed to %s\n",
+                        current->comm, current->pid, msg);
+}
+
 /*
  * Called in context of a new clone/fork from copy_process.
  */
 void uprobe_copy_process(struct task_struct *t)
 {
+        struct uprobe_task *utask = current->utask;
+        struct mm_struct *mm = current->mm;
+
         t->utask = NULL;
+
+        if (mm == t->mm || !utask || !utask->return_instances)
+                return;
+
+        if (dup_utask(t, utask))
+                return uprobe_warn(t, "dup ret instances");
 }
 
 /*