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authorVegard Nossum <vegard.nossum@oracle.com>2017-05-09 09:39:59 +0200
committerThomas Gleixner <tglx@linutronix.de>2017-05-22 22:21:16 +0200
commit4d6501dce079c1eb6bf0b1d8f528a5e81770109e (patch)
tree652f4e0fccb85573bde0ada8e74c15ff0295fb3f
parent5ea30e4e58040cfd6434c2f33dc3ea76e2c15b05 (diff)
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.iles@oracle.com> Fixes: 1da5c46fa965 ("kthread: Make struct kthread kmalloc'ed") Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Jamie Iles <jamie.iles@oracle.com> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20170509073959.17858-1-vegard.nossum@oracle.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--kernel/fork.c17
1 files 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