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Commit 7d672345 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

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: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8e2fe1d9

include/uapi/linux/bpf.h

+11 −0
Original line number Diff line number Diff line
@@ -287,6 +287,17 @@ 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,

};

net/core/filter.c

+53 −0
Original line number Diff line number Diff line
@@ -1491,6 +1491,12 @@ static u64 bpf_l4_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags) 
		return -EFAULT;



	switch (flags & BPF_F_HDR_FIELD_MASK) {

	case 0:

		if (unlikely(from != 0))

			return -EINVAL;



		inet_proto_csum_replace_by_diff(ptr, skb, to, is_pseudo);

		break;

	case 2:

		inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo);

		break;
@@ -1519,6 +1525,51 @@ const struct bpf_func_proto bpf_l4_csum_replace_proto = { 
	.arg5_type	= ARG_ANYTHING,

};



struct bpf_csum_scratchpad {

	__be32 diff[128];

};



static DEFINE_PER_CPU(struct bpf_csum_scratchpad, bpf_csum_sp);



static u64 bpf_csum_diff(u64 r1, u64 from_size, u64 r3, u64 to_size, u64 seed)

{

	struct bpf_csum_scratchpad *sp = this_cpu_ptr(&bpf_csum_sp);

	u64 diff_size = from_size + to_size;

	__be32 *from = (__be32 *) (long) r1;

	__be32 *to   = (__be32 *) (long) r3;

	int i, j = 0;



	/* This is quite flexible, some examples:

	 *

	 * from_size == 0, to_size > 0,  seed := csum --> pushing data

	 * from_size > 0,  to_size == 0, seed := csum --> pulling data

	 * from_size > 0,  to_size > 0,  seed := 0    --> diffing data

	 *

	 * Even for diffing, from_size and to_size don't need to be equal.

	 */

	if (unlikely(((from_size | to_size) & (sizeof(__be32) - 1)) ||

		     diff_size > sizeof(sp->diff)))

		return -EINVAL;



	for (i = 0; i < from_size / sizeof(__be32); i++, j++)

		sp->diff[j] = ~from[i];

	for (i = 0; i <   to_size / sizeof(__be32); i++, j++)

		sp->diff[j] = to[i];



	return csum_partial(sp->diff, diff_size, seed);

}



const struct bpf_func_proto bpf_csum_diff_proto = {

	.func		= bpf_csum_diff,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_STACK,

	.arg2_type	= ARG_CONST_STACK_SIZE_OR_ZERO,

	.arg3_type	= ARG_PTR_TO_STACK,

	.arg4_type	= ARG_CONST_STACK_SIZE_OR_ZERO,

	.arg5_type	= ARG_ANYTHING,

};



static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)

{

	struct sk_buff *skb = (struct sk_buff *) (long) r1, *skb2;
@@ -1849,6 +1900,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id) 
		return &bpf_skb_store_bytes_proto;

	case BPF_FUNC_skb_load_bytes:

		return &bpf_skb_load_bytes_proto;

	case BPF_FUNC_csum_diff:

		return &bpf_csum_diff_proto;

	case BPF_FUNC_l3_csum_replace:

		return &bpf_l3_csum_replace_proto;

	case BPF_FUNC_l4_csum_replace: