Commit-ID: 4d6501dce079c1eb6bf0b1d8f528a5e81770109e
Gitweb: http://git.kernel.org/tip/4d6501dce079c1eb6bf0b1d8f528a5e81770109e
Author: Vegard Nossum <vegard.nos...@oracle.com>
AuthorDate: Tue, 9 May 2017 09:39:59 +0200
Committer: Thomas Gleixner <t...@linutronix.de>
CommitDate: Mon, 22 May 2017 22:21:16 +0200
kthread: Fix use-after-free if kthread fork fails
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.i...@oracle.com>
Fixes: 1da5c46fa965 ("kthread: Make struct kthread kmalloc'ed")
Signed-off-by: Vegard Nossum <vegard.nos...@oracle.com>
Acked-by: Oleg Nesterov <o...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Jamie Iles <jamie.i...@oracle.com>
Cc: sta...@vger.kernel.org
Link: http://lkml.kernel.org/r/20170509073959.17858-1-vegard.nos...@oracle.com
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
kernel/fork.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index d681f8f..b7cdea1 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
