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([2a09:bac6:37a8:2696::3d8:30]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49541e9a7bbsm46976365e9.13.2026.07.16.03.06.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Jul 2026 03:06:09 -0700 (PDT) From: Matt Fleming To: Alexei Starovoitov , Daniel Borkmann Cc: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Lorenzo Bianconi , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , bpf@vger.kernel.org, netdev@vger.kernel.org, stable@vger.kernel.org, kernel-team@cloudflare.com, Matt Fleming Subject: [PATCH bpf] veth: convert frag_list skbs before running XDP Date: Thu, 16 Jul 2026 11:06:05 +0100 Message-ID: <20260716100605.939654-1-matt@readmodwrite.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Matt Fleming 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 frag_list 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 --- drivers/net/veth.c | 4 ++-- net/core/skbuff.c | 9 ++++----- 2 files changed, 6 insertions(+), 7 deletions(-) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index 1c5142149175..efb24aae1f26 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_shinfo(skb)->nr_frags || skb_has_frag_list(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..1e837d01a908 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -936,12 +936,11 @@ 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. + /* + * 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. */ - 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