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Commit 248d3a7b authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

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: default avatarMartin Cermak <mcermak@redhat.com>
Reported-by: default avatarDavid Smith <dsmith@redhat.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent af0d95af

kernel/events/uprobes.c

+43 −0
Original line number Diff line number Diff line
@@ -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");

}



/*