From 1079540e56b5dcd3eefbd136ce323cd2a72775c0 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Fri, 19 Feb 2016 23:05:23 +0100 Subject: bpf: add generic bpf_csum_diff helper For L4 checksums, we currently have bpf_l4_csum_replace() helper. It's currently limited to handle 2 and 4 byte changes in a header and feeds the from/to into inet_proto_csum_replace{2,4}() helpers of the kernel. When working with IPv6, for example, this makes it rather cumbersome to deal with, similarly when editing larger parts of a header. Instead, extend the API in a more generic way: For bpf_l4_csum_replace(), add a case for header field mask of 0 to change the checksum at a given offset through inet_proto_csum_replace_by_diff(), and provide a helper bpf_csum_diff() that can generically calculate a from/to diff for arbitrary amounts of data. This can be used in multiple ways: for the bpf_l4_csum_replace() only part, this even provides us with the option to insert precalculated diffs from user space f.e. from a map, or from bpf_csum_diff() during runtime. bpf_csum_diff() has a optional from/to stack buffer input, so we can calculate a diff by using a scratchbuffer for scenarios where we're inserting (from is NULL), removing (to is NULL) or diffing (from/to buffers don't need to be of equal size) data. Also, bpf_csum_diff() allows to feed a previous csum into csum_partial(), so the function can also be cascaded. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Chatur27 --- include/uapi/linux/bpf.h | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'include') diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index b629004f8000..73bd635ae195 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -291,6 +291,17 @@ enum bpf_func_id { * Return: >= 0 stackid on success or negative error */ BPF_FUNC_get_stackid, + + /** + * bpf_csum_diff(from, from_size, to, to_size, seed) - calculate csum diff + * @from: raw from buffer + * @from_size: length of from buffer + * @to: raw to buffer + * @to_size: length of to buffer + * @seed: optional seed + * Return: csum result + */ + BPF_FUNC_csum_diff, __BPF_FUNC_MAX_ID, }; -- cgit v1.2.3