ip_tunnel_xmit() and ip_md_tunnel_xmit() encapsulate packets that the tunnel forwards, and every failure on that path ends in the same plain kfree_skb(). The device counters separate them a little, but they are too coarse to act on: tx_errors alone covers an encapsulation failure, a routing failure, a lookup loop and a packet that is simply too big.
The last one deserves attention. tnl_update_pmtu() returns -E2BIG for a packet larger than the path MTU that has the DF bit set, after it has already sent an ICMP fragmentation needed back to the sender. That is path MTU discovery working as intended, yet it lands in tx_errors next to genuine failures, so a MTU black hole cannot be told from a broken route by looking at the counters. No new reason is needed for most of it: - SKB_DROP_REASON_PKT_TOO_BIG for the case above, - SKB_DROP_REASON_IP_OUTNOROUTES when no route is found, - SKB_DROP_REASON_RECURSION_LIMIT when the route points back at the tunnel device itself, which is the "dead loop on virtual device" that reason describes, - SKB_DROP_REASON_NOMEM when the headroom cannot be expanded, - SKB_DROP_REASON_NEIGH_CREATEFAIL when the NBMA neighbour lookup fails, SKB_DROP_REASON_NO_TX_TARGET when no destination can be derived at all, and SKB_DROP_REASON_UNHANDLED_PROTO for a payload that is neither IPv4 nor IPv6, - SKB_DROP_REASON_TUNNEL_TXINFO, which already documents a packet reaching an external mode device without metadata, for the collect_md path. Only the encapsulation failure has no fitting reason, so add SKB_DROP_REASON_IP_TUNNEL_ENCAP for it. Drop reasons on transmit are not new: vxlan already reports several of them from its xmit path, and ip_tunnel_core.c reports SKB_DROP_REASON_RECURSION_LIMIT. Assisted-by: Claude-Code:claude-opus-5 Signed-off-by: Anton Danilov <[email protected]> --- include/net/dropreason-core.h | 7 ++++++ net/ipv4/ip_tunnel.c | 41 ++++++++++++++++++++++++++++------- 2 files changed, 40 insertions(+), 8 deletions(-) diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h index d1fb52c1b0cb..2a2ac8767d68 100644 --- a/include/net/dropreason-core.h +++ b/include/net/dropreason-core.h @@ -133,6 +133,7 @@ FN(GRE_INVALID_HDR) \ FN(GRE_CSUM) \ FN(GRE_TUNNEL_NOT_FOUND) \ + FN(IP_TUNNEL_ENCAP) \ FNe(MAX) /** @@ -637,6 +638,12 @@ enum skb_drop_reason { * endpoints and the key the packet carries. */ SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND, + /** + * @SKB_DROP_REASON_IP_TUNNEL_ENCAP: failed to build the + * encapsulation header of a tunnel, e.g. an unknown or + * unregistered encapsulation type. + */ + SKB_DROP_REASON_IP_TUNNEL_ENCAP, /** * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which * shouldn't be used as a real 'reason' - only for tracing code gen diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index ab8bae8ba781..12d45f69c4d8 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -582,6 +582,7 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb, void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, u8 proto, int tunnel_hlen) { + enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED; struct ip_tunnel *tunnel = netdev_priv(dev); u32 headroom = sizeof(struct iphdr); struct ip_tunnel_info *tun_info; @@ -595,8 +596,10 @@ void ip_md_tunnel_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 tx_error; + } key = &tun_info->key; memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt)); inner_iph = (const struct iphdr *)skb_inner_network_header(skb); @@ -615,8 +618,10 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (!tunnel_hlen) tunnel_hlen = ip_encap_hlen(&tun_info->encap); - if (ip_tunnel_encap(skb, &tun_info->encap, &proto, &fl4) < 0) + if (ip_tunnel_encap(skb, &tun_info->encap, &proto, &fl4) < 0) { + reason = SKB_DROP_REASON_IP_TUNNEL_ENCAP; goto tx_error; + } use_cache = ip_tunnel_dst_cache_usable(skb, tun_info); if (use_cache) @@ -625,6 +630,7 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, rt = ip_route_output_key(tunnel->net, &fl4); if (IS_ERR(rt)) { DEV_STATS_INC(dev, tx_carrier_errors); + reason = SKB_DROP_REASON_IP_OUTNOROUTES; goto tx_error; } if (use_cache) @@ -634,6 +640,7 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (rt->dst.dev == dev) { ip_rt_put(rt); DEV_STATS_INC(dev, collisions); + reason = SKB_DROP_REASON_RECURSION_LIMIT; goto tx_error; } @@ -642,6 +649,7 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (tnl_update_pmtu(dev, skb, rt, df, inner_iph, tunnel_hlen, key->u.ipv4.dst, true)) { ip_rt_put(rt); + reason = SKB_DROP_REASON_PKT_TOO_BIG; goto tx_error; } @@ -659,6 +667,7 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, headroom += LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len; if (skb_cow_head(skb, headroom)) { ip_rt_put(rt); + reason = SKB_DROP_REASON_NOMEM; goto tx_dropped; } @@ -673,13 +682,14 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, tx_dropped: DEV_STATS_INC(dev, tx_dropped); kfree: - kfree_skb(skb); + kfree_skb_reason(skb, reason); } EXPORT_SYMBOL_GPL(ip_md_tunnel_xmit); void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, const struct iphdr *tnl_params, u8 protocol) { + enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED; struct ip_tunnel *tunnel = netdev_priv(dev); struct ip_tunnel_info *tun_info = NULL; const struct iphdr *inner_iph; @@ -707,9 +717,15 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (!skb_dst(skb)) { DEV_STATS_INC(dev, tx_fifo_errors); + reason = SKB_DROP_REASON_NO_TX_TARGET; goto tx_error; } + /* Only the branches below can derive a destination. If + * none of them matches, the payload protocol is not one + * this tunnel can carry. + */ + reason = SKB_DROP_REASON_UNHANDLED_PROTO; tun_info = skb_tunnel_info(skb); if (tun_info && (tun_info->mode & IP_TUNNEL_INFO_TX) && ip_tunnel_info_af(tun_info) == AF_INET && @@ -730,8 +746,10 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, neigh = dst_neigh_lookup(skb_dst(skb), &ipv6_hdr(skb)->daddr); - if (!neigh) + if (!neigh) { + reason = SKB_DROP_REASON_NEIGH_CREATEFAIL; goto tx_error; + } addr6 = (const struct in6_addr *)&neigh->primary_key; addr_type = ipv6_addr_type(addr6); @@ -748,8 +766,10 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, dst = addr6->s6_addr32[3]; } neigh_release(neigh); - if (do_tx_error_icmp) + if (do_tx_error_icmp) { + reason = SKB_DROP_REASON_NO_TX_TARGET; goto tx_error_icmp; + } } #endif else @@ -776,8 +796,10 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, tunnel->net, READ_ONCE(tunnel->parms.link), tunnel->fwmark, skb_get_hash(skb), 0); - if (ip_tunnel_encap(skb, &tunnel->encap, &protocol, &fl4) < 0) + if (ip_tunnel_encap(skb, &tunnel->encap, &protocol, &fl4) < 0) { + reason = SKB_DROP_REASON_IP_TUNNEL_ENCAP; goto tx_error; + } if (connected && md) { use_cache = ip_tunnel_dst_cache_usable(skb, tun_info); @@ -794,6 +816,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (IS_ERR(rt)) { DEV_STATS_INC(dev, tx_carrier_errors); + reason = SKB_DROP_REASON_IP_OUTNOROUTES; goto tx_error; } if (use_cache) @@ -807,6 +830,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (rt->dst.dev == dev) { ip_rt_put(rt); DEV_STATS_INC(dev, collisions); + reason = SKB_DROP_REASON_RECURSION_LIMIT; goto tx_error; } @@ -816,6 +840,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (tnl_update_pmtu(dev, skb, rt, df, inner_iph, 0, 0, false)) { ip_rt_put(rt); + reason = SKB_DROP_REASON_PKT_TOO_BIG; goto tx_error; } @@ -850,7 +875,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, if (skb_cow_head(skb, max_headroom)) { ip_rt_put(rt); DEV_STATS_INC(dev, tx_dropped); - kfree_skb(skb); + kfree_skb_reason(skb, SKB_DROP_REASON_NOMEM); return; } @@ -866,7 +891,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, #endif tx_error: DEV_STATS_INC(dev, tx_errors); - kfree_skb(skb); + kfree_skb_reason(skb, reason); } EXPORT_SYMBOL_GPL(ip_tunnel_xmit); -- 2.47.3
