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Date: Mon, 12 Jun 2017 17:24:11 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Vegard Nossum <vegard.nossum@...cle.com>,
Oleg Nesterov <oleg@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Andy Lutomirski <luto@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Jamie Iles <jamie.iles@...cle.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 4.11 044/150] kthread: Fix use-after-free if kthread fork fails
4.11-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vegard Nossum <vegard.nossum@...cle.com>
commit 4d6501dce079c1eb6bf0b1d8f528a5e81770109e upstream.
If a kthread forks (e.g. usermodehelper since commit 1da5c46fa965) but
fails in copy_process() between calling dup_task_struct() and setting
p->set_child_tid, then the value of p->set_child_tid will be inherited
from the parent and get prematurely freed by free_kthread_struct().
kthread()
- worker_thread()
- process_one_work()
| - call_usermodehelper_exec_work()
| - kernel_thread()
| - _do_fork()
| - copy_process()
| - dup_task_struct()
| - arch_dup_task_struct()
| - tsk->set_child_tid = current->set_child_tid // implied
| - ...
| - goto bad_fork_*
| - ...
| - free_task(tsk)
| - free_kthread_struct(tsk)
| - kfree(tsk->set_child_tid)
- ...
- schedule()
- __schedule()
- wq_worker_sleeping()
- kthread_data(task)->flags // UAF
The problem started showing up with commit 1da5c46fa965 since it reused
->set_child_tid for the kthread worker data.
A better long-term solution might be to get rid of the ->set_child_tid
abuse. The comment in set_kthread_struct() also looks slightly wrong.
Debugged-by: Jamie Iles <jamie.iles@...cle.com>
Fixes: 1da5c46fa965 ("kthread: Make struct kthread kmalloc'ed")
Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jamie Iles <jamie.iles@...cle.com>
Link: http://lkml.kernel.org/r/20170509073959.17858-1-vegard.nossum@oracle.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
kernel/fork.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1552,6 +1552,18 @@ static __latent_entropy struct task_stru
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);
@@ -1715,11 +1727,6 @@ static __latent_entropy struct task_stru
}
}
- 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
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