[PATCH net-next 09/11] ip_gre: add drop reasons to the transmit path
From: Anton Danilov
Date: Mon Aug 31 2026 - 20:42:15 EST
The five transmit functions of ip_gre collapse about twenty distinct
failures into a plain kfree_skb() and a tx_dropped increment, which says
nothing beyond "the tunnel did not send it".
No new reason is needed. The length helpers already compute one, so
pskb_inet_may_pull_reason() and pskb_may_pull_reason() are used instead
of their boolean wrappers, and the rest reuses:
- SKB_DROP_REASON_NOMEM for the headroom expansions, the offload
handling and the trims,
- SKB_DROP_REASON_TUNNEL_TXINFO for the collect_md paths, when the
metadata is missing or incomplete,
- SKB_DROP_REASON_UNHANDLED_PROTO for an ERSPAN version that is not
implemented,
- SKB_DROP_REASON_SKB_CSUM when the checksum starts before the data
the tunnel is about to send.
Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Anton Danilov <littlesmilingcloud@xxxxxxxxx>
---
net/ipv4/ip_gre.c | 101 +++++++++++++++++++++++++++++++++-------------
1 file changed, 74 insertions(+), 27 deletions(-)
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 4d9bb6d186ae..c45e9590c94d 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -511,23 +511,30 @@ static void gre_fb_xmit(struct sk_buff *skb, struct net_device *dev,
IP_TUNNEL_DECLARE_FLAGS(flags) = { };
struct ip_tunnel_info *tun_info;
const struct ip_tunnel_key *key;
+ enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
int tunnel_hlen;
tun_info = skb_tunnel_info(skb);
if (unlikely(!tun_info || !(tun_info->mode & IP_TUNNEL_INFO_TX) ||
- ip_tunnel_info_af(tun_info) != AF_INET))
+ ip_tunnel_info_af(tun_info) != AF_INET)) {
+ reason = SKB_DROP_REASON_TUNNEL_TXINFO;
goto err_free_skb;
+ }
key = &tun_info->key;
tunnel_hlen = gre_calc_hlen(key->tun_flags);
- if (skb_cow_head(skb, dev->needed_headroom))
+ if (skb_cow_head(skb, dev->needed_headroom)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto err_free_skb;
+ }
/* Push Tunnel header. */
if (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT,
- tunnel->parms.o_flags)))
+ tunnel->parms.o_flags))) {
+ reason = SKB_DROP_REASON_NOMEM;
goto err_free_skb;
+ }
__set_bit(IP_TUNNEL_CSUM_BIT, flags);
__set_bit(IP_TUNNEL_KEY_BIT, flags);
@@ -544,7 +551,7 @@ static void gre_fb_xmit(struct sk_buff *skb, struct net_device *dev,
return;
err_free_skb:
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
DEV_STATS_INC(dev, tx_dropped);
}
@@ -554,6 +561,7 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
IP_TUNNEL_DECLARE_FLAGS(flags) = { };
struct ip_tunnel_info *tun_info;
const struct ip_tunnel_key *key;
+ enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
struct erspan_metadata *md;
bool truncate = false;
__be16 proto;
@@ -563,29 +571,41 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
tun_info = skb_tunnel_info(skb);
if (unlikely(!tun_info || !(tun_info->mode & IP_TUNNEL_INFO_TX) ||
- ip_tunnel_info_af(tun_info) != AF_INET))
+ ip_tunnel_info_af(tun_info) != AF_INET)) {
+ reason = SKB_DROP_REASON_TUNNEL_TXINFO;
goto err_free_skb;
+ }
key = &tun_info->key;
- if (!test_bit(IP_TUNNEL_ERSPAN_OPT_BIT, tun_info->key.tun_flags))
+ if (!test_bit(IP_TUNNEL_ERSPAN_OPT_BIT, tun_info->key.tun_flags)) {
+ reason = SKB_DROP_REASON_TUNNEL_TXINFO;
goto err_free_skb;
- if (tun_info->options_len < sizeof(*md))
+ }
+ if (tun_info->options_len < sizeof(*md)) {
+ reason = SKB_DROP_REASON_TUNNEL_TXINFO;
goto err_free_skb;
+ }
md = ip_tunnel_info_opts(tun_info);
/* ERSPAN has fixed 8 byte GRE header */
version = md->version;
tunnel_hlen = 8 + erspan_hdr_len(version);
- if (skb_cow_head(skb, dev->needed_headroom))
+ if (skb_cow_head(skb, dev->needed_headroom)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto err_free_skb;
+ }
- if (gre_handle_offloads(skb, false))
+ if (gre_handle_offloads(skb, false)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto err_free_skb;
+ }
if (skb->len > dev->mtu + dev->hard_header_len) {
- if (pskb_trim(skb, dev->mtu + dev->hard_header_len))
+ if (pskb_trim(skb, dev->mtu + dev->hard_header_len)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto err_free_skb;
+ }
truncate = true;
}
@@ -617,6 +637,7 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
truncate, true);
proto = htons(ETH_P_ERSPAN2);
} else {
+ reason = SKB_DROP_REASON_UNHANDLED_PROTO;
goto err_free_skb;
}
@@ -629,7 +650,7 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct net_device *dev)
return;
err_free_skb:
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
DEV_STATS_INC(dev, tx_dropped);
}
@@ -663,8 +684,10 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
struct ip_tunnel *tunnel = netdev_priv(dev);
IP_TUNNEL_DECLARE_FLAGS(flags);
const struct iphdr *tnl_params;
+ enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
- if (!pskb_inet_may_pull(skb))
+ reason = pskb_inet_may_pull_reason(skb);
+ if (reason)
goto free_skb;
if (tunnel->collect_md) {
@@ -675,10 +698,13 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
if (dev->header_ops) {
int pull_len = tunnel->hlen + sizeof(struct iphdr);
- if (skb_cow_head(skb, 0))
+ if (skb_cow_head(skb, 0)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
- if (!pskb_may_pull(skb, pull_len))
+ reason = pskb_may_pull_reason(skb, pull_len);
+ if (reason)
goto free_skb;
tnl_params = (const struct iphdr *)skb->data;
@@ -688,25 +714,31 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
skb_reset_mac_header(skb);
if (skb->ip_summed == CHECKSUM_PARTIAL &&
- skb_checksum_start(skb) < skb->data)
+ skb_checksum_start(skb) < skb->data) {
+ reason = SKB_DROP_REASON_SKB_CSUM;
goto free_skb;
+ }
} else {
- if (skb_cow_head(skb, dev->needed_headroom))
+ if (skb_cow_head(skb, dev->needed_headroom)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
tnl_params = &tunnel->parms.iph;
}
ip_tunnel_flags_copy(flags, tunnel->parms.o_flags);
- if (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags)))
+ if (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags))) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
__gre_xmit(skb, dev, tnl_params, skb->protocol, flags);
return NETDEV_TX_OK;
free_skb:
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
DEV_STATS_INC(dev, tx_dropped);
return NETDEV_TX_OK;
}
@@ -716,10 +748,12 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
{
struct ip_tunnel *tunnel = netdev_priv(dev);
IP_TUNNEL_DECLARE_FLAGS(flags);
+ enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
bool truncate = false;
__be16 proto;
- if (!pskb_inet_may_pull(skb))
+ reason = pskb_inet_may_pull_reason(skb);
+ if (reason)
goto free_skb;
if (tunnel->collect_md) {
@@ -727,15 +761,21 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
return NETDEV_TX_OK;
}
- if (gre_handle_offloads(skb, false))
+ if (gre_handle_offloads(skb, false)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
- if (skb_cow_head(skb, dev->needed_headroom))
+ if (skb_cow_head(skb, dev->needed_headroom)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
if (skb->len > dev->mtu + dev->hard_header_len) {
- if (pskb_trim(skb, dev->mtu + dev->hard_header_len))
+ if (pskb_trim(skb, dev->mtu + dev->hard_header_len)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
truncate = true;
}
@@ -756,6 +796,7 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
truncate, true);
proto = htons(ETH_P_ERSPAN2);
} else {
+ reason = SKB_DROP_REASON_UNHANDLED_PROTO;
goto free_skb;
}
@@ -764,7 +805,7 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
return NETDEV_TX_OK;
free_skb:
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
DEV_STATS_INC(dev, tx_dropped);
return NETDEV_TX_OK;
}
@@ -774,8 +815,10 @@ static netdev_tx_t gre_tap_xmit(struct sk_buff *skb,
{
struct ip_tunnel *tunnel = netdev_priv(dev);
IP_TUNNEL_DECLARE_FLAGS(flags);
+ enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
- if (!pskb_inet_may_pull(skb))
+ reason = pskb_inet_may_pull_reason(skb);
+ if (reason)
goto free_skb;
if (tunnel->collect_md) {
@@ -785,17 +828,21 @@ static netdev_tx_t gre_tap_xmit(struct sk_buff *skb,
ip_tunnel_flags_copy(flags, tunnel->parms.o_flags);
- if (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags)))
+ if (gre_handle_offloads(skb, test_bit(IP_TUNNEL_CSUM_BIT, flags))) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
- if (skb_cow_head(skb, dev->needed_headroom))
+ if (skb_cow_head(skb, dev->needed_headroom)) {
+ reason = SKB_DROP_REASON_NOMEM;
goto free_skb;
+ }
__gre_xmit(skb, dev, &tunnel->parms.iph, htons(ETH_P_TEB), flags);
return NETDEV_TX_OK;
free_skb:
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
DEV_STATS_INC(dev, tx_dropped);
return NETDEV_TX_OK;
}
--
2.47.3