Re: [PATCH net v3] gso: validate gso_type in GSO handlers

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Fri, Jan 19, 2018 at 09:29:18AM -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.com>
> 
> Validate gso_type during segmentation as SKB_GSO_DODGY sources
> may pass packets where the gso_type does not match the contents.
> 
> Syzkaller was able to enter the SCTP gso handler with a packet of
> gso_type SKB_GSO_TCPV4.
> 
> On entry of transport layer gso handlers, verify that the gso_type
> matches the transport protocol.
> 
> Fixes: 90017accff61 ("sctp: Add GSO support")
> Link: http://lkml.kernel.org/r/<001a1137452496ffc305617e5fe0@google.com>
> Reported-by: syzbot+fee64147a25aecd48055@syzkaller.appspotmail.com
> Signed-off-by: Willem de Bruijn <willemb@google.com>

Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> 
> ---
> Similar checks existed until removed in commit 5c7cdf339af5 ("gso:
> Remove arbitrary checks for unsupported GSO"). But those were limited
> to the TSO path, not software GSO. I believe that this issue goes
> back further, hence the Fixes at the first user of virtio_net_hdr.

The Fixes is a bit earlier now, but okay.

> ---
>  net/ipv4/esp4_offload.c  | 3 +++
>  net/ipv4/tcp_offload.c   | 3 +++
>  net/ipv4/udp_offload.c   | 3 +++
>  net/ipv6/esp6_offload.c  | 3 +++
>  net/ipv6/tcpv6_offload.c | 3 +++
>  net/ipv6/udp_offload.c   | 3 +++
>  net/sctp/offload.c       | 3 +++
>  7 files changed, 21 insertions(+)
> 
> diff --git a/net/ipv4/esp4_offload.c b/net/ipv4/esp4_offload.c
> index b1338e576d00..29b333a62ab0 100644
> --- a/net/ipv4/esp4_offload.c
> +++ b/net/ipv4/esp4_offload.c
> @@ -122,6 +122,9 @@ static struct sk_buff *esp4_gso_segment(struct sk_buff *skb,
>  	if (!xo)
>  		goto out;
>  
> +	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_ESP))
> +		goto out;
> +
>  	seq = xo->seq.low;
>  
>  	x = skb->sp->xvec[skb->sp->len - 1];
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index b6a2aa1dcf56..4d58e2ce0b5b 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -32,6 +32,9 @@ static void tcp_gso_tstamp(struct sk_buff *skb, unsigned int ts_seq,
>  static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
>  					netdev_features_t features)
>  {
> +	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4))
> +		return ERR_PTR(-EINVAL);
> +
>  	if (!pskb_may_pull(skb, sizeof(struct tcphdr)))
>  		return ERR_PTR(-EINVAL);
>  
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 01801b77bd0d..ea6e6e7df0ee 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -203,6 +203,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
>  		goto out;
>  	}
>  
> +	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP))
> +		goto out;
> +
>  	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
>  		goto out;
>  
> diff --git a/net/ipv6/esp6_offload.c b/net/ipv6/esp6_offload.c
> index dd9627490c7c..f52c314d4c97 100644
> --- a/net/ipv6/esp6_offload.c
> +++ b/net/ipv6/esp6_offload.c
> @@ -149,6 +149,9 @@ static struct sk_buff *esp6_gso_segment(struct sk_buff *skb,
>  	if (!xo)
>  		goto out;
>  
> +	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_ESP))
> +		goto out;
> +
>  	seq = xo->seq.low;
>  
>  	x = skb->sp->xvec[skb->sp->len - 1];
> diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
> index d883c9204c01..278e49cd67d4 100644
> --- a/net/ipv6/tcpv6_offload.c
> +++ b/net/ipv6/tcpv6_offload.c
> @@ -46,6 +46,9 @@ static struct sk_buff *tcp6_gso_segment(struct sk_buff *skb,
>  {
>  	struct tcphdr *th;
>  
> +	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6))
> +		return ERR_PTR(-EINVAL);
> +
>  	if (!pskb_may_pull(skb, sizeof(*th)))
>  		return ERR_PTR(-EINVAL);
>  
> diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
> index a0f89ad76f9d..2a04dc9c781b 100644
> --- a/net/ipv6/udp_offload.c
> +++ b/net/ipv6/udp_offload.c
> @@ -42,6 +42,9 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
>  		const struct ipv6hdr *ipv6h;
>  		struct udphdr *uh;
>  
> +		if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP))
> +			goto out;
> +
>  		if (!pskb_may_pull(skb, sizeof(struct udphdr)))
>  			goto out;
>  
> diff --git a/net/sctp/offload.c b/net/sctp/offload.c
> index 275925b93b29..35bc7106d182 100644
> --- a/net/sctp/offload.c
> +++ b/net/sctp/offload.c
> @@ -45,6 +45,9 @@ static struct sk_buff *sctp_gso_segment(struct sk_buff *skb,
>  	struct sk_buff *segs = ERR_PTR(-EINVAL);
>  	struct sctphdr *sh;
>  
> +	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_SCTP))
> +		goto out;
> +
>  	sh = sctp_hdr(skb);
>  	if (!pskb_may_pull(skb, sizeof(*sh)))
>  		goto out;
> -- 
> 2.16.0.rc1.238.g530d649a79-goog
>