linux-kernel - net/dst_cache.c: preemption bug in net/dst

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Message-ID: <20190822195132.GA2100@bharath12345-Inspiron-5559>
Date:   Fri, 23 Aug 2019 01:21:33 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     davem@...emloft.net, gregkh@...uxfoundation.org,
        allison@...utok.net
Cc:     tglx@...utronix.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: net/dst_cache.c: preemption bug in net/dst_cache.c

Hi all,

I just want to bring attention to the syzbot bug [1]

Even though syzbot claims the bug to be in net/tipc, I feel it is in
net/dst_cache.c. Please correct me if I am wrong.

This bug is being triggered a lot of times by syzbot since the day it
was reported. Also given that this is core networking code, I felt it
was important to bring this to attention.

It looks like preemption needs to be disabled before using this_cpu_ptr
or maybe we would be better of using a get_cpu_var and put_cpu_var combo
here.

[1] https://syzkaller.appspot.com/bug?id=dc6352b92862eb79373fe03fdf9af5928753e057

Thank you
Bharath