netdev - Re: [PATCH net] fou, fou6: do not assume linear skbs

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Date:   Fri, 11 Jan 2019 15:15:07 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzkaller@...glegroups.com>,
        Sabrina Dubroca <sd@...asysnail.net>
Subject: Re: [PATCH net] fou, fou6: do not assume linear skbs

On Fri, 11 Jan 2019 04:55:52 -0800
Eric Dumazet <edumazet@...gle.com> wrote:

> Both gue_err() and gue6_err() incorrectly assume
> linear skbs. Fix them to use pskb_may_pull().

Thanks for fixing this! I stupidly didn't suspect we could get
non-linear skbs there. Just two things:

> +++ b/net/ipv4/fou.c
> @@ -1020,10 +1020,11 @@ static int gue_err(struct sk_buff *skb, u32 info)
>  {
>  	int transport_offset = skb_transport_offset(skb);
>  	struct guehdr *guehdr;
> -	size_t optlen;
> +	size_t len, optlen;
>  	int ret;
>  
> -	if (skb->len < sizeof(struct udphdr) + sizeof(struct guehdr))
> +	len = sizeof(struct udphdr) + sizeof(struct guehdr);
> +	if (!pskb_may_pull(skb, len))
>  		return -EINVAL;
>  
>  	guehdr = (struct guehdr *)&udp_hdr(skb)[1];
> @@ -1058,6 +1059,10 @@ static int gue_err(struct sk_buff *skb, u32 info)
>  
>  	optlen = guehdr->hlen << 2;
>  
> +	if (!pskb_may_pull(skb, len + optlen)
                                             ^ ) missing

> +		return -EINVAL;
> +
> +	guehdr = (struct guehdr *)&udp_hdr(skb)[1];
>  	if (validate_gue_flags(guehdr, optlen))
>  		return -EINVAL;
>  
> diff --git a/net/ipv6/fou6.c b/net/ipv6/fou6.c
> index 7da7bf3b7fe3953eeb60addfffd6687c4da582c4..320413af4890641e7199d7d7102e7d8c2794d557 100644
> --- a/net/ipv6/fou6.c
> +++ b/net/ipv6/fou6.c
> @@ -90,10 +90,11 @@ static int gue6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
>  {
>  	int transport_offset = skb_transport_offset(skb);
>  	struct guehdr *guehdr;
> -	size_t optlen;
> +	size_t len, optlen;
>  	int ret;
>  
> -	if (skb->len < sizeof(struct udphdr) + sizeof(struct guehdr))
> +	len = sizeof(struct udphdr) + sizeof(struct guehdr);
> +	if (!pskb_may_pull(skb, len))
>  		return -EINVAL;
>  
>  	guehdr = (struct guehdr *)&udp_hdr(skb)[1];
> @@ -128,6 +129,10 @@ static int gue6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
>  
>  	optlen = guehdr->hlen << 2;
>  
> +	if (!pskb_may_pull(skb, len + optlen)
                                             ^ ) missing

> +		return -EINVAL;
> +
> +	guehdr = (struct guehdr *)&udp_hdr(skb)[1];
>  	if (validate_gue_flags(guehdr, optlen))
>  		return -EINVAL;
>  

-- 
Stefano