[GIT pull core fix for 4.12

From: Thomas Gleixner
Date: Sat May 27 2017 - 04:32:52 EST


Linus,

please pull the latest core-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus

A single fix which prevents a use after free when kthread fork fails.

Thanks,

tglx

------------------>
Vegard Nossum (1):
kthread: Fix use-after-free if kthread fork fails


kernel/fork.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index d681f8f10d2d..b7cdea10239c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1553,6 +1553,18 @@ static __latent_entropy struct task_struct *copy_process(
if (!p)
goto fork_out;

+ /*
+ * This _must_ happen before we call free_task(), i.e. before we jump
+ * to any of the bad_fork_* labels. This is to avoid freeing
+ * p->set_child_tid which is (ab)used as a kthread's data pointer for
+ * kernel threads (PF_KTHREAD).
+ */
+ p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
+ /*
+ * Clear TID on mm_release()?
+ */
+ p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
+
ftrace_graph_init_task(p);

rt_mutex_init_task(p);
@@ -1716,11 +1728,6 @@ static __latent_entropy struct task_struct *copy_process(
}
}

- p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
- /*
- * Clear TID on mm_release()?
- */
- p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
#ifdef CONFIG_BLOCK
p->plug = NULL;
#endif