gso: validate gso_type in GSO handlers

gso: validate gso_type in GSO handlers

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/<[email protected]>
Reported-by: [email protected]
Signed-off-by: Willem de Bruijn <[email protected]>
Acked-by: Jason Wang <[email protected]>
Reviewed-by: Marcelo Ricardo Leitner <[email protected]>
Signed-off-by: David S. Miller <[email protected]>