From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Thu, 14 May 2020 12:51:25 +0200
Subject: xdp: Allow bpf_xdp_adjust_tail() to grow packet size
Patch-mainline: v5.8-rc1
Git-commit: c8741e2bfe872425ea6f10bb6f7dc1d67bc60c3a
References: bsc#1177028
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
Acked-by: Gary Lin <glin@suse.com>
---
include/uapi/linux/bpf.h | 4 ++--
net/core/filter.c | 11 +++++++++--
2 files changed, 11 insertions(+), 4 deletions(-)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3411,12 +3411,19 @@ static const struct bpf_func_proto bpf_x
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;