linux-kernel - Re: [PATCH] ipv4: fib: avoid NULL dereference

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Message-ID: <deb5ea83-120f-9181-089d-8ae64e23dc0d@gmail.com>
Date:   Fri, 6 Jul 2018 08:39:11 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Mark Rutland <mark.rutland@....com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: fib: avoid NULL dereference



On 07/06/2018 07:57 AM, Mark Rutland wrote:
> On Fri, Jul 06, 2018 at 07:47:04AM -0700, Eric Dumazet wrote:
>>
>>
>> On 07/06/2018 07:28 AM, Mark Rutland wrote:
>>> In tnode_free() we iterate over a callback_head list with a while loop.
>>> At the start of the loop body we generate the next head pointer, and at
>>> the end of the loop body we generate the tn pointer for the next
>>> iteration of the loop by using container_of() on the head pointer to
>>> find the tnode, and deriving the kv pointer from this.
>>>
>>> In the final iteration of the loop, this means that we derive a pointer
>>> from NULL, which is undefined behaviour, which UBSAN detects:
>>
>> There is no dereference, your patch title is misleading.
>>
>> UBSAN might be fooled, not the C compiler.
> 
> I'm happy to change the title to "avoid undefined behaviour".
> 

Are you planning to change this as well ?

include/linux/stddef.h:19:#define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER)

(And probably dozens of other locations)