Subject: Re: [PATCH] net: af_packet: Validate parameter size for PACKET_HDRLEN control message

From: Daniel Borkmann <[email-masked]>
Date: Wed, 27 Feb 2013 21:22:17 +0100

On 02/27/2013 08:46 PM, Guenter Roeck wrote:
> Building af_packet may fail with
>
> In function ‘copy_from_user’,
>      inlined from ‘packet_getsockopt’ at
>      net/packet/af_packet.c:3215:21:
> arch/x86/include/asm/uaccess_32.h:211:26: error: call to
>      ‘copy_from_user_overflow’ declared with attribute error: copy_from_user()
>      buffer size is not provably correct
>
> if built with W=1 due to a missing parameter size validation.
>
> Signed-off-by: Guenter Roeck <[email-masked]>
> ---
>   net/packet/af_packet.c |    2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index c7bfeff..1976b23 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -3210,6 +3210,8 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
>   		val = po->tp_version;
>   		break;
>   	case PACKET_HDRLEN:
> +		if (len < sizeof(int))
> +			return -EINVAL;

I think this could break some user space applications here, those who e.g. only pass
an uint16_t to packet_getsockopt with PACKET_HDRLEN.

>   		if (len > sizeof(int))
>   			len = sizeof(int);
>   		if (copy_from_user(&val, optval, len))