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

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Message-ID: <20180706145728.57utqqrjzq7iupnh@lakrids.cambridge.arm.com>
Date:   Fri, 6 Jul 2018 15:57:29 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     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 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".

Thanks,
Mark.