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

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Date:   Fri, 6 Jul 2018 07:47:04 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:     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 07:28 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.