linux-kernel - Re: [PATCH] Freeing dst when the reference count <0 causes general protection fault, it could be a major security flaw as rogue app can modify dst to crash kernel.

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Message-ID: <1410603214.25850.5.camel@localhost>
Date:	Sat, 13 Sep 2014 12:13:34 +0200
From:	Hannes Frederic Sowa <hannes@...hat.com>
To:	Shakil A Khan <shakilk1729@...il.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	edumazet@...gle.com, davem@...emloft.net
Subject: Re: [PATCH] Freeing dst when the reference count <0 causes general
 protection fault, it could be a major security flaw as rogue app can modify
 dst to crash kernel.

On Sa, 2014-09-13 at 01:27 -0700, Shakil A Khan wrote:
> Signed-off-by: Shakil A Khan <shakilk1729@...il.com>
> ---
>  net/core/dst.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/core/dst.c b/net/core/dst.c
> index a028409..6a848b0 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -284,7 +284,10 @@ void dst_release(struct dst_entry *dst)
>  		int newrefcnt;
>  
>  		newrefcnt = atomic_dec_return(&dst->__refcnt);
> -		WARN_ON(newrefcnt < 0);
> +
> +		if (WARN(newrefcnt < 0, "dst reference count less than zero"))
> +			return;
> +
>  		if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt)
>  			call_rcu(&dst->rcu_head, dst_destroy_rcu);
>  	}

So change this to a memory leak which also has reliable concerns...

You could just change this to a BUG_ON, but this will also allow a rogue
app to kill the kernel.


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