Commit b32cc5b9 authored by Nikita V. Shirokov's avatar Nikita V. Shirokov Committed by Daniel Borkmann

bpf: adding bpf_xdp_adjust_tail helper

Adding new bpf helper which would allow us to manipulate
xdp's data_end pointer, and allow us to reduce packet's size
indended use case: to generate ICMP messages from XDP context,
where such message would contain truncated original packet.
Signed-off-by: default avatarNikita V. Shirokov <tehnerd@tehnerd.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 0c90f224
......@@ -755,6 +755,13 @@ union bpf_attr {
* @addr: pointer to struct sockaddr to bind socket to
* @addr_len: length of sockaddr structure
* Return: 0 on success or negative error code
*
* int bpf_xdp_adjust_tail(xdp_md, delta)
* Adjust the xdp_md.data_end by delta. Only shrinking of packet's
* size is supported.
* @xdp_md: pointer to xdp_md
* @delta: A negative integer to be added to xdp_md.data_end
* Return: 0 on success or negative on error
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
......@@ -821,7 +828,8 @@ union bpf_attr {
FN(msg_apply_bytes), \
FN(msg_cork_bytes), \
FN(msg_pull_data), \
FN(bind),
FN(bind), \
FN(xdp_adjust_tail),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
......
......@@ -2725,6 +2725,30 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = {
.arg2_type = ARG_ANYTHING,
};
BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
{
void *data_end = xdp->data_end + offset;
/* only shrinking is allowed for now. */
if (unlikely(offset >= 0))
return -EINVAL;
if (unlikely(data_end < xdp->data + ETH_HLEN))
return -EINVAL;
xdp->data_end = data_end;
return 0;
}
static const struct bpf_func_proto bpf_xdp_adjust_tail_proto = {
.func = bpf_xdp_adjust_tail,
.gpl_only = false,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_CTX,
.arg2_type = ARG_ANYTHING,
};
BPF_CALL_2(bpf_xdp_adjust_meta, struct xdp_buff *, xdp, int, offset)
{
void *meta = xdp->data_meta + offset;
......@@ -3074,7 +3098,8 @@ bool bpf_helper_changes_pkt_data(void *func)
func == bpf_l4_csum_replace ||
func == bpf_xdp_adjust_head ||
func == bpf_xdp_adjust_meta ||
func == bpf_msg_pull_data)
func == bpf_msg_pull_data ||
func == bpf_xdp_adjust_tail)
return true;
return false;
......@@ -3888,6 +3913,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_xdp_redirect_proto;
case BPF_FUNC_redirect_map:
return &bpf_xdp_redirect_map_proto;
case BPF_FUNC_xdp_adjust_tail:
return &bpf_xdp_adjust_tail_proto;
default:
return bpf_base_func_proto(func_id);
}
......
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