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xdp: Allow bpf_xdp_adjust_tail() to grow packet size

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Finally, after all drivers have a frame size, allow BPF-helper
bpf_xdp_adjust_tail() to grow or extend packet size at frame tail.

Remember that helper/macro xdp_data_hard_end have reserved some
tailroom.  Thus, this helper makes sure that the BPF-prog don't have
access to this tailroom area.

V2: Remove one chicken check and use WARN_ONCE for other

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/158945348530.97035.12577148209134239291.stgit@firesoul
This commit is contained in:
Jesper Dangaard Brouer 2020-05-14 12:51:25 +02:00 committed by Alexei Starovoitov
parent d628ee4fef
commit c8741e2bfe
2 changed files with 11 additions and 4 deletions
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4
include/uapi/linux/bpf.h
View File

@ -2015,8 +2015,8 @@ union bpf_attr {
* int bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)
* Description
* Adjust (move) *xdp_md*\ **->data_end** by *delta* bytes. It is
* only possible to shrink the packet as of this writing,
* therefore *delta* must be a negative integer.
* possible to both shrink and grow the packet tail.
* Shrink done via *delta* being a negative integer.
*
* A call to this helper is susceptible to change the underlying
* packet buffer. Therefore, at load time, all checks on pointers

11
net/core/filter.c
View File

@ -3411,12 +3411,19 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = {
BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
{
void *data_hard_end = xdp_data_hard_end(xdp); /* use xdp->frame_sz */
void *data_end = xdp->data_end + offset;
/* only shrinking is allowed for now. */
if (unlikely(offset >= 0))
/* Notice that xdp_data_hard_end have reserved some tailroom */
if (unlikely(data_end > data_hard_end))
return -EINVAL;
/* ALL drivers MUST init xdp->frame_sz, chicken check below */
if (unlikely(xdp->frame_sz > PAGE_SIZE)) {
WARN_ONCE(1, "Too BIG xdp->frame_sz = %d\n", xdp->frame_sz);
return -EINVAL;
}
if (unlikely(data_end < xdp->data + ETH_HLEN))
return -EINVAL;