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[34.48.4.250]) by smtp.gmail.com with ESMTPSA id 00721157ae682-81fa27985cbsm13921187b3.16.2026.07.29.00.46.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jul 2026 00:46:55 -0700 (PDT) Date: Wed, 29 Jul 2026 03:46:54 -0400 From: Willem de Bruijn To: Qihang , netdev@vger.kernel.org Cc: willemdebruijn.kernel@gmail.com, daniel.zahka@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, stable@vger.kernel.org, Qihang Message-ID: In-Reply-To: <20260729030122.21462-3-q.h.hack.winter@gmail.com> References: <20260729030122.21462-1-q.h.hack.winter@gmail.com> <20260729030122.21462-3-q.h.hack.winter@gmail.com> Subject: Re: [PATCH net v4 2/2] packet: use consistent hard_header_len in TX_RING send path Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Qihang wrote: > tpacket_snd() reads dev->hard_header_len independently for skb > allocation and header construction in tpacket_fill_skb(). Concurrent > netdevice reconfiguration can therefore make the reserved headroom > smaller than the amount later pushed, or make copylen - hard_header_len > negative. > > Snapshot hard_header_len once before processing ring frames and use it > for the frame limit, headroom allocation, copy length, and skb > construction. Pass the snapshot to tpacket_fill_skb(). Reset copylen for > each frame so a previous frame cannot retain a larger construction > length. > > The separate SOCK_DGRAM consistency problem between hard_header_len and > header_ops->create is not addressed here. > > Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap") > Cc: stable@vger.kernel.org > Signed-off-by: Qihang > --- > net/packet/af_packet.c | 20 ++++++++++++-------- > 1 file changed, 12 insertions(+), 8 deletions(-) > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 88674a6e868c..8ee0a80fdcea 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -2574,6 +2574,7 @@ static int packet_snd_vnet_parse(struct msghdr *msg, size_t *len, > static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb, > void *frame, struct net_device *dev, void *data, int tp_len, > __be16 proto, unsigned char *addr, int hlen, int copylen, > + int hard_header_len, > const struct sockcm_cookie *sockc) > { > union tpacket_uhdr ph; > @@ -2605,8 +2606,8 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb, > } else if (copylen) { > int hdrlen = min_t(int, copylen, tp_len); > > - skb_push(skb, dev->hard_header_len); > - skb_put(skb, copylen - dev->hard_header_len); > + skb_push(skb, hard_header_len); > + skb_put(skb, copylen - hard_header_len); > err = skb_store_bits(skb, 0, data, hdrlen); > if (unlikely(err)) > return err; > @@ -2737,7 +2738,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) > void *data; > int len_sum = 0; > int status = TP_STATUS_AVAILABLE; > - int hlen, tlen, copylen = 0; > + int hard_header_len, hlen, tlen, copylen = 0; > long timeo; > > mutex_lock(&po->pg_vec_lock); > @@ -2784,8 +2785,9 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) > goto out_put; > } > > + hard_header_len = READ_ONCE(dev->hard_header_len); > if (po->sk.sk_socket->type == SOCK_RAW) > - reserve = dev->hard_header_len; > + reserve = hard_header_len; > size_max = po->tx_ring.frame_size > - (po->tp_hdrlen - sizeof(struct sockaddr_ll)); > > @@ -2822,8 +2824,9 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) > goto tpacket_error; > > status = TP_STATUS_SEND_REQUEST; > - hlen = LL_RESERVED_SPACE(dev); > + hlen = LL_RESERVED_SPACE_EX(dev, hard_header_len); > tlen = dev->needed_tailroom; > + copylen = 0; Why is this introduced? > if (vnet_hdr_sz) { > data += vnet_hdr_sz; > tp_len -= vnet_hdr_sz;