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@xxxxxxxxxx>
---
include/uapi/linux/bpf.h | 4 ++--
net/core/filter.c | 11 +++++++++--
2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7bbf1b65be10..621a64c3cd75 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1969,8 +1969,8 @@ 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
diff --git a/net/core/filter.c b/net/core/filter.c
index 7d6ceaa54d21..40e749d57cc1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3422,12 +3422,19 @@ 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;
