Re: [PATCH bpf v2] veth: convert frag_list skbs before running XDP
From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2026-07-21 10:05:48
Also in:
bpf, stable
From: Matt Fleming <redacted>
A frag_list skb can reach veth with data_len set but nr_frags zero.
veth_convert_skb_to_xdp_buff() only converts skbs that are shared,
locked, have frags[], or do not have enough headroom. It later uses
skb_is_nonlinear() to decide whether to set XDP_FLAGS_HAS_FRAGS and
xdp_frags_size.
That exposes frag_list data to XDP as if it were stored in frags[], but
frags[] is empty. AF_XDP copy mode can then trust the bogus XDP fragment
metadata, walk an empty fragment entry, and crash in memcpy() from
__xsk_rcv().
Route non-linear skbs through skb_pp_cow_data() before exposing them to
XDP, and only advertise XDP frags when the resulting skb has frags[].
skb_copy_bits() already handles frag_list input, and skb_pp_cow_data()
builds frags[] output with skb_add_rx_frag(), which is the
representation XDP multi-buffer expects.
Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Fleming <redacted>Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
quoted hunk ↗ jump to hunk
--- Changes in v2: - Use skb_is_nonlinear() in veth_convert_skb_to_xdp_buff(). - Move the skb_pp_cow_data() comment into kerneldoc. drivers/net/veth.c | 4 ++-- net/core/skbuff.c | 16 ++++++++++------ 2 files changed, 12 insertions(+), 8 deletions(-)diff --git a/drivers/net/veth.c b/drivers/net/veth.c index 1c5142149175..00e34afd858e 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c@@ -756,7 +756,7 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, u32 frame_sz; if (skb_shared(skb) || skb_head_is_locked(skb) || - skb_shinfo(skb)->nr_frags || + skb_is_nonlinear(skb) || skb_headroom(skb) < XDP_PACKET_HEADROOM) { if (skb_pp_cow_data(rq->page_pool, pskb, XDP_PACKET_HEADROOM)) goto drop;@@ -771,7 +771,7 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, xdp_prepare_buff(xdp, skb->head, skb_headroom(skb), skb_headlen(skb), true); - if (skb_is_nonlinear(skb)) { + if (skb_shinfo(skb)->nr_frags) { skb_shinfo(skb)->xdp_frags_size = skb->data_len; xdp_buff_set_frags_flag(xdp); } else {diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 18dabb4e9cfa..66f57131633a 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c@@ -927,6 +927,16 @@ static void skb_clone_fraglist(struct sk_buff *skb) skb_get(list); } +/** + * skb_pp_cow_data() - copy skb data into page-pool backed storage + * @pool: page pool to allocate from + * @pskb: pointer to skb pointer, replaced with the copied skb on success + * @headroom: headroom to reserve in the copied skb + * + * skb_copy_bits() handles both frags[] and frag_list input. If the copied + * skb remains non-linear, it uses frags[], which is the representation used + * by XDP multi-buffer. + */ int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb, unsigned int headroom) {@@ -936,12 +946,6 @@ int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb, int err, i, head_off; void *data; - /* XDP does not support fraglist so we need to linearize - * the skb. - */ - if (skb_has_frag_list(skb)) - return -EOPNOTSUPP; - max_head_size = SKB_WITH_OVERHEAD(PAGE_SIZE - headroom); if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE) return -ENOMEM;-- 2.43.0
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