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Subject[PATCH 4/5] 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.

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

Cc: stable@vger.kernel.org # 3.9+
Reported-by: Martin Cermak <mcermak@redhat.com>
Reported-by: David Smith <dsmith@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/uprobes.c | 43 +++++++++++++++++++++++++++++++++++++++++++
1 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c836135..67b65c8 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");
}

/*
--
1.5.5.1


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