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Date: Wed, 09 Jan 2019 12:04:41 +1100
From: Michael Ellerman <>
To: Eric Dumazet <>,
Subject: Re: Re: Linux Kernel 4.20(21) deadlock vulnerability.

Eric Dumazet <> writes:
> Hello Entropy Moe
> syzbot reported dozens of similar issues involving printk
> Not sure why this would be a security concern ?

It's a local DOS, so that's a security concern for some people.

But AFAICT the lockup warning only happens because the injected SLAB
failure tries to call printk(). If there'd been a real allocation
failure it would have just returned an error and there'd be no issue.

If you modify the reproducer to also do:

	write_file("/sys/kernel/debug/failslab/verbose", "0");

Then it shouldn't do the printk() and hopefully there'll be no lockup


> On Tue, Jan 8, 2019 at 7:08 AM Entropy Moe <> wrote:
>> Hello,
>> I wanted to let you know that there seem to be a deadlock vulnerability on the linux kernel 4.20.
>> I am attaching the result report from syzkaller which also got the c code for replication.
>> thank you,

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