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Davide Caratti says: ==================== net: fix CRC32c in the forwarding path Current kernel allows offloading CRC32c computation when SCTP packets are generated, setting skb->ip_summed to CHECKSUM_PARTIAL, if the underlying device features have NETIF_F_SCTP_CRC set. However, after these packets are forwarded, they may land on a device where CRC32c offloading is not available: as a consequence, transmission is done with wrong CRC32c. It's not possible to use sctp_compte_cksum() in the forwarding path and in most drivers, because it needs symbols exported by libcrc32c module. Patch 1 and 2 of this series try to solve this problem, introducing a new helper function, namely skb_crc32c_csum_help(), that can be used to resolve CHECKSUM_PARTIAL when crc32c is needed instead of Internet Checksum. Currently, we need to parse the packet headers to understand what algorithm is needed to resolve CHECKSUM_PARTIAL. We can speedup things by storing this information in the skb metadata, and use it to call an appropriate helper (skb_checksum_help or skb_crc32c_csum_help), or leave the packet unmodified when the NIC is able to offload the checksum computation. Patch 3 deprecates skb->csum_bad to free one bit in skb metadata; patch 4 introduces skb->csum_not_inet, providing skb with an indication on the algorithm needed to resolve CHECKSUM_PARTIAL. Patch 5 and 6 fix the kernel forwarding path and openvswitch datapath, where skb_checksum_help was unconditionally called to resolve CHECKSUM_PARTIAL, thus generating wrong CRC32c in forwarded SCTP packets. Finally, patch 7 updates documentation to provide a better description of possible values of skb->ip_summed. Some further work is still possible: * drivers that parse the packet header to correctly resolve CHECKSUM_PARTIAL (e.g. ixgbe_tx_csum()) can benefit from testing skb->csum_not_inet to avoid calling ip_hdr(skb)->protocol or ixgbe_ipv6_csum_is_sctp(skb). * drivers that call skb_checksum_help() to resolve CHECKSUM_PARTIAL can call skb_csum_hwoffload_help to avoid corrupting SCTP packets. Changes v2->v3: - patch 1/7: more standard declaration of stub variables Changes v1->v2: - none Changes RFCv4->v1: - patch 2/7: use WARN_ON_ONCE() instead of BUG_ON(), and avoid computing CRC32c on the error path. - patch 3/7: don't invert tests on the values of same_flow and NAPI_GRO_CB(skb)->flush in dev_gro_receive(), it's useless and it breaks GRO functionality as reported by kernel test robot. ==================== Signed-off-by: David S. Miller <davem@davemloft.net> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.