Re: [Crash] unhandled kernel memory read from unreadable memory

From: Cong Wang <xiyou.wangcong@gmail.com>
To: Peter Geis <pgwipeout@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	bpf@vger.kernel.org
Subject: Re: [Crash] unhandled kernel memory read from unreadable memory
Date: Sat, 13 Jun 2020 10:52:08 -0700	[thread overview]
Message-ID: <CAM_iQpUNNs4fzLAT8xmhbg+dhM0gdS+HVOtFD+fMJegeSHgUFA@mail.gmail.com> (raw)
In-Reply-To: <CAMdYzYpKEOWCjb-kZj=HAkzQ0_QNs4N_6pXz1qPb1YQ2Xh5Jsg@mail.gmail.com>

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Hello,

On Sat, Jun 13, 2020 at 5:41 AM Peter Geis <pgwipeout@gmail.com> wrote:
>
> Good Morning,
>
> Last night I started experiencing crashes on my home server.
> I updated to 5.6.17 from 5.6.15 a few days ago but I'm not sure if
> that is related.
> The crash occurred four times between last night and this morning.

Yeah, this is known. Can you test the attached patch?

Thanks.

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diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 6c9c6ac83936..c01245a19ea2 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6438,9 +6438,6 @@ void cgroup_sk_alloc_disable(void)
 
 void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
 {
-	if (cgroup_sk_alloc_disabled)
-		return;
-
 	/* Socket clone path */
 	if (skcd->val) {
 		/*
@@ -6453,6 +6450,9 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
 		return;
 	}
 
+	if (cgroup_sk_alloc_disabled)
+		return;
+
 	/* Don't associate the sock with unrelated interrupted task's cgroup. */
 	if (in_interrupt())
 		return;
