From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Oleg Nesterov <oleg@redhat.com>
Cc: serge@hallyn.com,
syzbot <syzbot+a9ac39bf55329e206219@syzkaller.appspotmail.com>,
jmorris@namei.org, keescook@chromium.org,
linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org,
syzkaller-bugs@googlegroups.com
Subject: Re: KASAN: use-after-free Read in task_is_descendant
Date: Thu, 25 Oct 2018 22:14:59 +0900 [thread overview]
Message-ID: <d11bc954-5a30-e6bd-1668-866a187e0aac@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20181025121709.GD3725@redhat.com>
On 2018/10/25 21:17, Oleg Nesterov wrote:
>>> And yes, task_is_descendant() can hit the dead child, if nothing else it can
>>> be killed. This can explain the kasan report.
>>
>> The kasan is reporting that child->real_parent (or maybe child->real_parent->real_parent
>> or child->real_parent->real_parent->real_parent ...) was pointing to already freed memory,
>> isn't it?
>
> Yes. and you know, I am all confused. I no longer can understand you :/
Why don't we need to check every time like shown below?
Why checking only once is sufficient?
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -285,7 +285,7 @@ static int task_is_descendant(struct task_struct *parent,
rcu_read_lock();
if (!thread_group_leader(parent))
parent = rcu_dereference(parent->group_leader);
- while (walker->pid > 0) {
+ while (pid_alive(walker) && walker->pid > 0) {
if (!thread_group_leader(walker))
walker = rcu_dereference(walker->group_leader);
if (walker == parent) {
next prev parent reply other threads:[~2018-10-25 13:15 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-21 7:10 KASAN: use-after-free Read in task_is_descendant syzbot
2018-10-21 7:12 ` Tetsuo Handa
2018-10-22 9:54 ` Oleg Nesterov
2018-10-22 10:06 ` Tetsuo Handa
2018-10-22 13:46 ` Oleg Nesterov
2018-10-25 2:15 ` Tetsuo Handa
2018-10-25 11:13 ` Oleg Nesterov
2018-10-25 11:36 ` Kees Cook
2018-10-25 12:05 ` Oleg Nesterov
2018-10-25 11:47 ` Tetsuo Handa
2018-10-25 12:17 ` Oleg Nesterov
2018-10-25 13:01 ` Oleg Nesterov
2018-10-26 16:09 ` Kees Cook
2018-10-29 12:23 ` Oleg Nesterov
2018-10-29 15:05 ` yama: unsafe usage of ptrace_relation->tracer Oleg Nesterov
2019-01-10 11:05 ` Tetsuo Handa
2019-01-10 18:47 ` Kees Cook
2019-01-16 17:40 ` Oleg Nesterov
2018-10-25 13:14 ` Tetsuo Handa [this message]
2018-10-25 15:55 ` KASAN: use-after-free Read in task_is_descendant Oleg Nesterov
2018-10-25 16:25 ` Oleg Nesterov
2018-10-26 12:23 ` Tetsuo Handa
2018-10-26 13:04 ` Oleg Nesterov
2018-10-26 13:51 ` Tetsuo Handa
2018-10-26 14:39 ` Oleg Nesterov
2018-10-26 15:04 ` Tetsuo Handa
2018-10-26 15:22 ` Oleg Nesterov
2018-10-25 8:19 ` Kees Cook
2018-10-25 11:52 ` Oleg Nesterov
2018-11-10 3:25 ` syzbot
2018-11-10 11:46 ` syzbot
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