[PATCH net v2] packet: use consistent header lengths in raw send paths
From: Qihang <hidden>
Date: 2026-07-26 09:21:31
Also in:
stable
Subsystem:
networking [general], packet sockets, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Willem de Bruijn, Linus Torvalds
packet_snd(), tpacket_snd(), and packet_sendmsg_spkt() read
dev->hard_header_len multiple times while allocating and constructing an
skb. Device reconfiguration can change this value concurrently, for
example through bonding device type changes.
For SOCK_RAW, packet_snd() can save a larger value in reserve and later
allocate headroom using a smaller value. Moving skb->data back by reserve
then places it before skb->head, and the following copy from userspace can
attempt an out-of-bounds write.
tpacket_snd() similarly uses independent values for allocation and for
the skb_push()/skb_put() operations in tpacket_fill_skb(). The legacy
packet_sendmsg_spkt() path also calculates its reservation and header
offset from separate reads before dropping the RCU read lock to allocate
the skb. A larger offset than reservation can move skb->data before
skb->head, while mixed TX-ring values can also make
copylen - hard_header_len negative.
Read hard_header_len once for each send operation and use that value for
RAW allocation and construction. The trigger requires racing an
AF_PACKET sender with privileged netdevice reconfiguration.
The separate SOCK_DGRAM consistency problem between hard_header_len and
header_ops->create is not addressed here.
Fixes: b84bbaf7a6c8 ("packet: in packet_snd start writing at link layer allocation")
Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap")
Cc: stable@vger.kernel.org
Signed-off-by: Qihang <redacted>
---
v2:
- Cover packet_sendmsg_spkt().
- Limit snapshot-based calculations to RAW construction; leave DGRAM
unchanged for a separate fix.
Link to v1: https://lore.kernel.org/netdev/20260721084935.12312-1-q.h.hack.winter@gmail.com/ (local)
---
net/packet/af_packet.c | 64 ++++++++++++++++++++++++++++++------------
1 file changed, 46 insertions(+), 18 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e75d2932475a..d23898f24641 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c@@ -1953,6 +1953,7 @@ static int packet_sendmsg_spkt(struct socket *sock, struct msghdr *msg, struct net_device *dev; struct sockcm_cookie sockc; __be16 proto = 0; + unsigned int hard_header_len = 0; int err; int extra_len = 0;
@@ -1996,15 +1997,21 @@ static int packet_sendmsg_spkt(struct socket *sock, struct msghdr *msg, } extra_len = 4; /* We're doing our own CRC */ } + if (!skb) + hard_header_len = READ_ONCE(dev->hard_header_len); err = -EMSGSIZE; - if (len > dev->mtu + dev->hard_header_len + VLAN_HLEN + extra_len) + if (len > dev->mtu + hard_header_len + VLAN_HLEN + extra_len) goto out_unlock; if (!skb) { - size_t reserved = LL_RESERVED_SPACE(dev); + size_t reserved; int tlen = dev->needed_tailroom; - unsigned int hhlen = dev->header_ops ? dev->hard_header_len : 0; + unsigned int hhlen = READ_ONCE(dev->header_ops) ? + hard_header_len : 0; + + reserved = ((hard_header_len + READ_ONCE(dev->needed_headroom)) & + ~(HH_DATA_MOD - 1)) + HH_DATA_MOD; rcu_read_unlock(); skb = sock_wmalloc(sk, len + reserved + tlen, 0, GFP_KERNEL);
@@ -2569,6 +2576,7 @@ 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;
@@ -2600,8 +2608,8 @@ 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;
@@ -2732,7 +2740,7 @@ 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 = 0, hlen, tlen, copylen = 0; long timeo; mutex_lock(&po->pg_vec_lock);
@@ -2779,8 +2787,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) goto out_put; } - if (po->sk.sk_socket->type == SOCK_RAW) - reserve = dev->hard_header_len; + if (po->sk.sk_socket->type == SOCK_RAW) { + hard_header_len = READ_ONCE(dev->hard_header_len); + reserve = hard_header_len; + } size_max = po->tx_ring.frame_size - (po->tp_hdrlen - sizeof(struct sockaddr_ll));
@@ -2817,7 +2827,12 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) goto tpacket_error; status = TP_STATUS_SEND_REQUEST; - hlen = LL_RESERVED_SPACE(dev); + if (po->sk.sk_socket->type == SOCK_RAW) + hlen = ((hard_header_len + + READ_ONCE(dev->needed_headroom)) & + ~(HH_DATA_MOD - 1)) + HH_DATA_MOD; + else + hlen = LL_RESERVED_SPACE(dev); tlen = dev->needed_tailroom; if (vnet_hdr_sz) { data += vnet_hdr_sz;
@@ -2835,10 +2850,14 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) vnet_hdr.hdr_len); has_vnet_hdr = true; } - copylen = max_t(int, copylen, dev->hard_header_len); + if (po->sk.sk_socket->type == SOCK_RAW) + copylen = max_t(int, copylen, hard_header_len); + else + copylen = max_t(int, copylen, dev->hard_header_len); skb = sock_alloc_send_skb(&po->sk, hlen + tlen + sizeof(struct sockaddr_ll) + - (copylen - dev->hard_header_len), + (copylen - (po->sk.sk_socket->type == SOCK_RAW ? + hard_header_len : dev->hard_header_len)), !need_wait, &err); if (unlikely(skb == NULL)) {
@@ -2848,7 +2867,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) goto out_status; } tp_len = tpacket_fill_skb(po, skb, ph, dev, data, tp_len, proto, - addr, hlen, copylen, &sockc); + addr, hlen, copylen, hard_header_len, + &sockc); if (likely(tp_len >= 0) && tp_len > dev->mtu + reserve && !vnet_hdr_sz &&
@@ -2956,7 +2976,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) int offset = 0; struct packet_sock *po = pkt_sk(sk); int vnet_hdr_sz = READ_ONCE(po->vnet_hdr_sz); - int hlen, tlen, linear; + int hard_header_len = 0, hlen, tlen, linear; int extra_len = 0; /*
@@ -2996,14 +3016,17 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) goto out_unlock; } - if (sock->type == SOCK_RAW) - reserve = dev->hard_header_len; if (vnet_hdr_sz) { err = packet_snd_vnet_parse(msg, &len, &vnet_hdr, vnet_hdr_sz); if (err) goto out_unlock; } + if (sock->type == SOCK_RAW) { + hard_header_len = READ_ONCE(dev->hard_header_len); + reserve = hard_header_len; + } + if (unlikely(sock_flag(sk, SOCK_NOFCS))) { if (!netif_supports_nofcs(dev)) { err = -EPROTONOSUPPORT;
@@ -3018,10 +3041,15 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) goto out_unlock; err = -ENOBUFS; - hlen = LL_RESERVED_SPACE(dev); + if (sock->type == SOCK_RAW) + hlen = ((hard_header_len + READ_ONCE(dev->needed_headroom)) & + ~(HH_DATA_MOD - 1)) + HH_DATA_MOD; + else + hlen = LL_RESERVED_SPACE(dev); tlen = dev->needed_tailroom; linear = __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len); - linear = max(linear, min_t(int, len, dev->hard_header_len)); + linear = max(linear, min_t(int, len, sock->type == SOCK_RAW ? + hard_header_len : dev->hard_header_len)); skb = packet_alloc_skb(sk, hlen + tlen, hlen, len, linear, msg->msg_flags & MSG_DONTWAIT, &err); if (skb == NULL)
@@ -3037,7 +3065,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) } else if (reserve) { skb_reserve(skb, -reserve); if (len < reserve + sizeof(struct ipv6hdr) && - dev->min_header_len != dev->hard_header_len) + dev->min_header_len != hard_header_len) skb_reset_network_header(skb); }
--
2.50.1 (Apple Git-155)