[PATCH RFC v1 08/15] xdp: allow bpf_xdp_adjust_tail() to grow packet size
From: Jesper Dangaard Brouer <hidden>
Date: 2020-03-17 17:30:07
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
FIXME: This patch MUST be LAST after all drivers have been updated!!! 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. Signed-off-by: Jesper Dangaard Brouer <redacted> --- include/uapi/linux/bpf.h | 4 ++-- net/core/filter.c | 18 ++++++++++++++++-- 2 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 14dc4f9fb3c8..1fa6ab616ec3 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h@@ -1942,8 +1942,8 @@ 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 4a08c9fb2be7..0ceddee0c678 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -3409,12 +3409,26 @@ 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); 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; + /* DANGER: ALL drivers MUST be converted to init xdp->frame_sz + * - Adding some chicken checks below + * - Will (likely) not be for upstream + */ + if (unlikely(xdp->frame_sz < (xdp->data_end - xdp->data_hard_start))) { + WARN(1, "Too small xdp->frame_sz = %d\n", xdp->frame_sz); + return -EINVAL; + } + if (unlikely(xdp->frame_sz > PAGE_SIZE)) { + WARN(1, "Too BIG xdp->frame_sz = %d\n", xdp->frame_sz); + return -EINVAL; + } + if (unlikely(data_end < xdp->data + ETH_HLEN)) return -EINVAL;