lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <20200120083518.GL23018@gauss3.secunet.de> Date: Mon, 20 Jan 2020 09:35:18 +0100 From: Steffen Klassert <steffen.klassert@...unet.com> To: Willem de Bruijn <willemdebruijn.kernel@...il.com> CC: David Miller <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>, Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, Network Development <netdev@...r.kernel.org> Subject: Re: [PATCH net-next 3/4] net: Support GRO/GSO fraglist chaining. On Wed, Jan 15, 2020 at 10:43:08AM -0500, Willem de Bruijn wrote: > > > > Maybe we can be conservative here and do a full > > > > __copy_skb_header for now. The initial version > > > > does not necessarily need to be the most performant > > > > version. We could try to identify the correct subset > > > > of header fields later then. > > > > > > We should probably aim for the right set from the start. If you think > > > this set is it, let's keep it. > > > > I'd prefer to do a full __copy_skb_header for now and think a bit > > longer if that what I chose is really the correct subset. > > Ok > > > > > > > I had to set ip_summed to CHECKSUM_UNNECESSARY on GRO to > > > > > > make sure the noone touches the checksum of the head > > > > > > skb. Otherise netfilter etc. tries to touch the csum. > > > > > > > > > > > > Before chaining I make sure that ip_summed and csum_level is > > > > > > the same for all chained skbs and here I restore the original > > > > > > value from nskb. > > > > > > > > > > This is safe because the skb_gro_checksum_validate will have validated > > > > > already on CHECKSUM_PARTIAL? What happens if there is decap or encap > > > > > in the path? We cannot revert to CHECKSUM_PARTIAL after that, I > > > > > imagine. > > > > > > > > Yes, the checksum is validated with skb_gro_checksum_validate. If the > > > > packets are UDP encapsulated, they are segmented before decapsulation. > > > > Original values are already restored. If an additional encapsulation > > > > happens, the encap checksum will be calculated after segmentation. > > > > Original values are restored before that. > > > > > > I was wondering more about additional other encapsulation protocols. > > > > > > >From a quick read, it seems like csum_level is associated only with > > > CHECKSUM_UNNECESSARY. > > > > > > What if a device returns CHECKSUM_COMPLETE for packets with a tunnel > > > that is decapsulated before forwarding. Say, just VLAN. That gets > > > untagged in __netif_receive_skb_core with skb_vlan_untag calling > > > skb_pull_rcsum. After segmentation the ip_summed is restored, with > > > skb->csum still containing the unmodified csum that includes the VLAN > > > tag? > > > > Hm, that could be really a problem. So setting CHECKSUM_UNNECESSARY > > should be ok, but restoring the old values are not. Our checksum > > magic is rather complex, it's hard to get it right for all possible > > cases. Maybe we can just set CHECKSUM_UNNECESSARY for all packets > > and keep this value after segmentation. > > Note that I'm not 100% sure that the issue can occur. But it seems likely. > > Yes, inverse CHECKSUM_UNNECESSARY conversion after verifying the checksum is > probably the way to go. Inverse, because it is the opposite of > __skb_gro_checksum_convert. I'm not sure if I understand what you mean here. I'd do the following for fraglist GRO in udp4_gro_complete: if (skb->ip_summed == CHECKSUM_UNNECESSARY) { if (skb->csum_level < SKB_MAX_CSUM_LEVEL) skb->csum_level++; } else { skb->ip_summed = CHECKSUM_UNNECESSARY; skb->csum_level = 0; } and then copy these values to the segments after segmentation.
Powered by blists - more mailing lists