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veth: Adjust hard_start offset on redirect XDP frames

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[ 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: 9fc8d518d9 ("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@firesoul
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jesper Dangaard Brouer 2020-05-14 12:49:43 +02:00 committed by Greg Kroah-Hartman
parent 868b8e43a0
commit b6c90a7d0a
1 changed files with 4 additions and 4 deletions
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8
drivers/net/veth.c
View file

@ -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;