netdev - Re: [PATCH net-next ] net: ipv4: memset addr before calling copy_to

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Date:	Mon, 09 Nov 2015 11:09:06 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Loganaden Velvindron <logan@...ndsys.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next ] net: ipv4: memset addr before calling
 copy_to_user()

Hello,

On Mon, Nov 9, 2015, at 07:52, Loganaden Velvindron wrote:
> zero addr before calling copy_to_user()
>  
> Signed-off-by: Loganaden Velvindron <logan@...ndsys.com>
> ---
>  net/ipv4/ip_sockglue.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> index c3c359a..d7a5a8b 100644
> --- a/net/ipv4/ip_sockglue.c
> +++ b/net/ipv4/ip_sockglue.c
> @@ -1373,6 +1373,7 @@ static int do_ip_getsockopt(struct sock *sk, int
> level, int optname,
>  	case IP_MULTICAST_IF:
>  	{
>  		struct in_addr addr;
> +               memset(&addr, 0, sizeof(addr));
>  		len = min_t(unsigned int, len, sizeof(struct in_addr));
>  		addr.s_addr = inet->mc_addr;
>  		release_sock(sk);

There is no possibility we leak any unwanted data to user space here.

If you are not sure if sizeof(addr) > sizeof(addr.s_addr) use a
designated initializer:

addr = { .s_addr = inet->mc_addr };

which clears all other non-initialized elements. But here we are very
certain.

We do not do defensive programming, we try to do logical things, and
only logical things.
— Eric Dumazet (Thanks to Dan Carpenter.)

Bye,
Hannes
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