linux-kernel - Re: [PATCH] netlink: fix overrun in attribute iteration

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Date:	Thu, 11 Sep 2008 15:04:34 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	vegard.nossum@...il.com
Cc:	netdev@...r.kernel.org, tgraf@...g.ch, penberg@...helsinki.fi,
	mingo@...e.hu, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netlink: fix overrun in attribute iteration

From: Vegard Nossum <vegard.nossum@...il.com>
Date: Thu, 11 Sep 2008 22:59:33 +0200

> A short example illustrating this point is here:
> 
>   #include <stdio.h>
> 
>   main(void)
>   {
>           printf("%d\n", -1 >= sizeof(int));
>   }
> 
> ...which prints "1".

Someone should print that out on a huge poster, it's a good
example of why C promotion rules suck :)

> This patch adds a cast in front of the sizeof so that GCC will make
> a signed comparison and fix the illegal memory dereference. With the
> patch applied, there is no kmemcheck report.
> 
> Cc: Thomas Graf <tgraf@...g.ch>
> Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>

Thomas, please review.

> diff --git a/include/net/netlink.h b/include/net/netlink.h
> index 18024b8..208fe5a 100644
> --- a/include/net/netlink.h
> +++ b/include/net/netlink.h
> @@ -702,7 +702,7 @@ static inline int nla_len(const struct nlattr *nla)
>   */
>  static inline int nla_ok(const struct nlattr *nla, int remaining)
>  {
> -	return remaining >= sizeof(*nla) &&
> +	return remaining >= (int) sizeof(*nla) &&
>  	       nla->nla_len >= sizeof(*nla) &&
>  	       nla->nla_len <= remaining;
>  }
> -- 
> 1.5.5.1
> 
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