From: Jesper Dangaard Brouer brouer@redhat.com
[ Upstream commit 5c8572251fabc5bb49fd623c064e95a9daf6a3e3 ]
When native XDP redirect into a veth device, the frame arrives in the xdp_frame structure. It is then processed in veth_xdp_rcv_one(), which can run a new XDP bpf_prog on the packet. Doing so requires converting xdp_frame to xdp_buff, but the tricky part is that xdp_frame memory area is located in the top (data_hard_start) memory area that xdp_buff will point into.
The current code tried to protect the xdp_frame area, by assigning xdp_buff.data_hard_start past this memory. This results in 32 bytes less headroom to expand into via BPF-helper bpf_xdp_adjust_head().
This protect step is actually not needed, because BPF-helper bpf_xdp_adjust_head() already reserve this area, and don't allow BPF-prog to expand into it. Thus, it is safe to point data_hard_start directly at xdp_frame memory area.
Fixes: 9fc8d518d9d5 ("veth: Handle xdp_frames in xdp napi ring") Reported-by: Mao Wenan maowenan@huawei.com Signed-off-by: Jesper Dangaard Brouer brouer@redhat.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Toshiaki Makita toshiaki.makita1@gmail.com Acked-by: Toke Høiland-Jørgensen toke@redhat.com Link: https://lore.kernel.org/bpf/158945338331.97035.5923525383710752178.stgit@fir... Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/veth.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/net/veth.c b/drivers/net/veth.c index 41a00cd76955..2abbad1abaf2 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -377,13 +377,15 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, unsigned int *xdp_xmit) { void *hard_start = frame->data - frame->headroom; - void *head = hard_start - sizeof(struct xdp_frame); int len = frame->len, delta = 0; struct xdp_frame orig_frame; struct bpf_prog *xdp_prog; unsigned int headroom; struct sk_buff *skb;
+ /* bpf_xdp_adjust_head() assures BPF cannot access xdp_frame area */ + hard_start -= sizeof(struct xdp_frame); + rcu_read_lock(); xdp_prog = rcu_dereference(rq->xdp_prog); if (likely(xdp_prog)) { @@ -405,7 +407,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, break; case XDP_TX: orig_frame = *frame; - xdp.data_hard_start = head; xdp.rxq->mem = frame->mem; if (unlikely(veth_xdp_tx(rq->dev, &xdp) < 0)) { trace_xdp_exception(rq->dev, xdp_prog, act); @@ -417,7 +418,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, goto xdp_xmit; case XDP_REDIRECT: orig_frame = *frame; - xdp.data_hard_start = head; xdp.rxq->mem = frame->mem; if (xdp_do_redirect(rq->dev, &xdp, xdp_prog)) { frame = &orig_frame; @@ -437,7 +437,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, rcu_read_unlock();
headroom = sizeof(struct xdp_frame) + frame->headroom - delta; - skb = veth_build_skb(head, headroom, len, 0); + skb = veth_build_skb(hard_start, headroom, len, 0); if (!skb) { xdp_return_frame(frame); goto err;