On Tue, Aug 22, 2017 at 11:28:28AM -0700, Eric Dumazet wrote: > On Tue, 2017-08-22 at 11:01 -0700, David Miller wrote: > > From: "Michael S. Tsirkin" <m...@redhat.com> > > Date: Tue, 22 Aug 2017 20:55:56 +0300 > > > > > Which reminds me that skb_linearize in net core seems to be > > > fundamentally racy - I suspect that if skb is cloned, and someone is > > > trying to use the shared frags while another thread calls skb_linearize, > > > we get some use after free bugs which likely mostly go undetected > > > because the corrupted packets mostly go on wire and get dropped > > > by checksum code. > > > > Indeed, it does assume that the skb from which the clone was made > > never has it's geometry changed. > > > > I don't think even the TCP retransmit queue has this guarantee. > > TCP retransmit makes sure to avoid that. > > if (skb_unclone(skb, GFP_ATOMIC)) > return -ENOMEM; > > ( Before cloning again skb ) > >
I'm pretty sure not all users of skb_clone or generally __pskb_pull_tail are careful like this. E.g. skb_cow_data actually intentionally pulls pages when skb is cloned. -- MST
