From: Anton Danilov <littlesmilingcloud@gmail.com>
To: netdev@vger.kernel.org
Cc: "David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>, David Ahern <dsahern@kernel.org>,
Ido Schimmel <idosch@nvidia.com>,
Andrew Lunn <andrew+netdev@lunn.ch>,
linux-kernel@vger.kernel.org
Subject: [PATCH net-next v5 06/14] gre: make gre_parse_header() report a drop reason
Date: Wed, 30 Sep 2026 21:39:02 +0300 [thread overview]
Message-ID: <20260930183910.3151873-7-littlesmilingcloud@gmail.com> (raw)
In-Reply-To: <20260930183910.3151873-1-littlesmilingcloud@gmail.com>
gre_parse_header() returns -EINVAL for every failure and its receive
callers turn that into a plain kfree_skb(). The only detail they could
get so far was the csum_err flag, which none of them actually reads:
both ip_gre and ip6_gre declare it, pass it in and then ignore it.
Make gre_parse_header() return the drop reason instead, with
SKB_NOT_DROPPED_YET for a valid header, and let the two receive paths
report it. The header length it used to return is already stored in
tpi->hdr_len, so the callers take it from there. The reasons are:
- SKB_DROP_REASON_TUNNEL_INVALID_HDR, for a header carrying an
unsupported version or the routing bit; its description gets a GRE
example,
- SKB_DROP_REASON_GRE_CSUM, a new reason for a checksum error, like the
existing TCP_CSUM, UDP_CSUM, ICMP_CSUM and IP_CSUM,
- the reason pskb_may_pull_reason() returns when the header cannot be
pulled: SKB_DROP_REASON_PKT_TOO_SMALL for a short packet and
SKB_DROP_REASON_NOMEM for an allocation failure. The byte that tells
WCCPv1 from WCCPv2 is read with skb_header_pointer() instead, which
only fails on a short packet, so that check returns
SKB_DROP_REASON_PKT_TOO_SMALL.
gre_rcv() in the demux reports SKB_DROP_REASON_TUNNEL_INVALID_HDR for a
version it cannot dispatch at all, as gre_parse_header() does for a
nonzero version in ip6_gre, which does not go through the demux. A
valid version whose handler is not registered, such as PPTP, is
reported as SKB_DROP_REASON_UNHANDLED_PROTO.
csum_err had a second use: the ICMP error handlers pass NULL for it, so
that a checksum failure does not reject the header and the rest of it is
still parsed, as they only get a part of the original packet. That came
with commit b0350d51f001 ("ip_gre: fix parsing gre header in ipgre_err")
and becomes an explicit ignore_csum_err argument. The checksum is
still computed either way. As the function is exported, the comment
above it becomes a kernel-doc comment, which describes the argument.
Tunnel lookup failures and the other drops of the receive handlers
still report SKB_DROP_REASON_NOT_SPECIFIED at this point; the following
patches convert them.
The reason follows the rule of ip_tunnel_rcv(). gre_rcv() of the demux
and of ip6_gre sets it in its first statement, so it is not initialized
there; ip_gre's gre_rcv() initializes it, which its looped back
multicast check relies on, as it drops before the header is parsed. All
three store the result of a helper in the reason, so their drop labels
fall back to SKB_DROP_REASON_NOT_SPECIFIED.
Assisted-by: LLM
Signed-off-by: Anton Danilov <littlesmilingcloud@gmail.com>
---
include/net/dropreason-core.h | 4 +++
include/net/gre.h | 5 +--
net/ipv4/gre_demux.c | 65 ++++++++++++++++++++++++-----------
net/ipv4/ip_gre.c | 18 +++++-----
net/ipv6/ip6_gre.c | 18 +++++-----
5 files changed, 70 insertions(+), 40 deletions(-)
diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 85aaa58c3ecb..0d963f18a21e 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -131,6 +131,7 @@
FN(RECURSION_LIMIT) \
FN(TUNNEL_OPT_MISMATCH) \
FN(TUNNEL_OLD_SEQ) \
+ FN(GRE_CSUM) \
FNe(MAX)
/**
@@ -544,6 +545,7 @@ enum skb_drop_reason {
* @SKB_DROP_REASON_TUNNEL_INVALID_HDR: tunnel header is invalid. E.g.:
* 1) VXLAN reserved fields are not zero
* 2) VXLAN "I" flag is not set
+ * 3) GRE version is not supported or the routing bit is set
*/
SKB_DROP_REASON_TUNNEL_INVALID_HDR,
/**
@@ -631,6 +633,8 @@ enum skb_drop_reason {
* remote endpoint restarted and reset its sequence numbering.
*/
SKB_DROP_REASON_TUNNEL_OLD_SEQ,
+ /** @SKB_DROP_REASON_GRE_CSUM: GRE checksum error */
+ SKB_DROP_REASON_GRE_CSUM,
/**
* @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/include/net/gre.h b/include/net/gre.h
index b55f67ecd2fc..b5dbe00ab15e 100644
--- a/include/net/gre.h
+++ b/include/net/gre.h
@@ -32,8 +32,9 @@ struct gre_protocol {
int gre_add_protocol(const struct gre_protocol *proto, u8 version);
int gre_del_protocol(const struct gre_protocol *proto, u8 version);
-int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
- bool *csum_err, __be16 proto, int nhs);
+enum skb_drop_reason
+gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
+ bool ignore_csum_err, __be16 proto, int nhs);
static inline bool netif_is_gretap(const struct net_device *dev)
{
diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index 96fd7dc6d82d..fccdaa240f46 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -56,28 +56,47 @@ int gre_del_protocol(const struct gre_protocol *proto, u8 version)
}
EXPORT_SYMBOL_GPL(gre_del_protocol);
-/* Fills in tpi and returns header length to be pulled.
- * Note that caller must use pskb_may_pull() before pulling GRE header.
+/**
+ * gre_parse_header() - parse the GRE header of a packet
+ * @skb: the packet; the GRE header starts @nhs bytes past skb->data
+ * @tpi: filled in with the fields of the header, and with the length of
+ * the header to be pulled in tpi->hdr_len
+ * @ignore_csum_err: do not reject the header when its checksum does not
+ * match. The ICMP error handlers set it, as they only get a part of the
+ * original packet; the checksum is still computed and the rest of the
+ * header is parsed.
+ * @proto: the protocol to report for a WCCP payload, ETH_P_IP or
+ * ETH_P_IPV6
+ * @nhs: the offset of the GRE header from skb->data
+ *
+ * The caller must use pskb_may_pull() before pulling the GRE header.
+ *
+ * Return: SKB_NOT_DROPPED_YET, or the reason to drop the packet if the
+ * header is rejected.
*/
-int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
- bool *csum_err, __be16 proto, int nhs)
+enum skb_drop_reason
+gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
+ bool ignore_csum_err, __be16 proto, int nhs)
{
const struct gre_base_hdr *greh;
+ enum skb_drop_reason reason;
__be32 *options;
int hdr_len;
- if (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr))))
- return -EINVAL;
+ reason = pskb_may_pull_reason(skb, nhs + sizeof(struct gre_base_hdr));
+ if (unlikely(reason))
+ return reason;
greh = (struct gre_base_hdr *)(skb->data + nhs);
if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
- return -EINVAL;
+ return SKB_DROP_REASON_TUNNEL_INVALID_HDR;
gre_flags_to_tnl_flags(tpi->flags, greh->flags);
hdr_len = gre_calc_hlen(tpi->flags);
- if (!pskb_may_pull(skb, nhs + hdr_len))
- return -EINVAL;
+ reason = pskb_may_pull_reason(skb, nhs + hdr_len);
+ if (reason)
+ return reason;
greh = (struct gre_base_hdr *)(skb->data + nhs);
tpi->proto = greh->protocol;
@@ -87,9 +106,8 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
if (!skb_checksum_simple_validate(skb)) {
skb_checksum_try_convert(skb, IPPROTO_GRE,
null_compute_pseudo);
- } else if (csum_err) {
- *csum_err = true;
- return -EINVAL;
+ } else if (!ignore_csum_err) {
+ return SKB_DROP_REASON_GRE_CSUM;
}
options++;
@@ -117,7 +135,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
val = skb_header_pointer(skb, nhs + hdr_len,
sizeof(_val), &_val);
if (!val)
- return -EINVAL;
+ return SKB_DROP_REASON_PKT_TOO_SMALL;
tpi->proto = proto;
if ((*val & 0xF0) != 0x40)
hdr_len += 4;
@@ -132,29 +150,35 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
greh->protocol == htons(ETH_P_ERSPAN2)) {
struct erspan_base_hdr *ershdr;
- if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
- return -EINVAL;
+ reason = pskb_may_pull_reason(skb,
+ nhs + hdr_len + sizeof(*ershdr));
+ if (reason)
+ return reason;
ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
tpi->key = cpu_to_be32(get_session_id(ershdr));
}
- return hdr_len;
+ return SKB_NOT_DROPPED_YET;
}
EXPORT_SYMBOL(gre_parse_header);
static int gre_rcv(struct sk_buff *skb)
{
const struct gre_protocol *proto;
+ enum skb_drop_reason reason;
u8 ver;
int ret;
- if (!pskb_may_pull(skb, 12))
+ reason = pskb_may_pull_reason(skb, 12);
+ if (reason)
goto drop;
ver = skb->data[1]&0x7f;
- if (ver >= GREPROTO_MAX)
+ if (ver >= GREPROTO_MAX) {
+ reason = SKB_DROP_REASON_TUNNEL_INVALID_HDR;
goto drop;
+ }
rcu_read_lock();
proto = rcu_dereference(gre_proto[ver]);
@@ -167,11 +191,12 @@ static int gre_rcv(struct sk_buff *skb)
drop_nohandler:
rcu_read_unlock();
dev_core_stats_rx_nohandler_inc(skb->dev);
- kfree_skb(skb);
+ kfree_skb_reason(skb, SKB_DROP_REASON_UNHANDLED_PROTO);
return NET_RX_DROP;
drop:
+ reason = reason ?: SKB_DROP_REASON_NOT_SPECIFIED;
dev_core_stats_rx_dropped_inc(skb->dev);
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
return NET_RX_DROP;
}
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 3ee437fa3eae..a1b44007b1d7 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -237,8 +237,8 @@ static void gre_err(struct sk_buff *skb, u32 info)
const int code = icmp_hdr(skb)->code;
struct tnl_ptk_info tpi;
- if (gre_parse_header(skb, &tpi, NULL, htons(ETH_P_IP),
- iph->ihl * 4) < 0)
+ if (gre_parse_header(skb, &tpi, true, htons(ETH_P_IP),
+ iph->ihl * 4))
return;
if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED) {
@@ -439,9 +439,8 @@ static int ipgre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi,
static int gre_rcv(struct sk_buff *skb)
{
+ enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
struct tnl_ptk_info tpi;
- bool csum_err = false;
- int hdr_len;
#ifdef CONFIG_NET_IPGRE_BROADCAST
if (ipv4_is_multicast(ip_hdr(skb)->daddr)) {
@@ -451,25 +450,26 @@ static int gre_rcv(struct sk_buff *skb)
}
#endif
- hdr_len = gre_parse_header(skb, &tpi, &csum_err, htons(ETH_P_IP), 0);
- if (hdr_len < 0)
+ reason = gre_parse_header(skb, &tpi, false, htons(ETH_P_IP), 0);
+ if (reason)
goto drop;
if (unlikely(tpi.proto == htons(ETH_P_ERSPAN) ||
tpi.proto == htons(ETH_P_ERSPAN2))) {
- if (erspan_rcv(skb, &tpi, hdr_len) == PACKET_RCVD)
+ if (erspan_rcv(skb, &tpi, tpi.hdr_len) == PACKET_RCVD)
return 0;
goto out;
}
- if (ipgre_rcv(skb, &tpi, hdr_len) == PACKET_RCVD)
+ if (ipgre_rcv(skb, &tpi, tpi.hdr_len) == PACKET_RCVD)
return 0;
out:
icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
drop:
+ reason = reason ?: SKB_DROP_REASON_NOT_SPECIFIED;
dev_core_stats_rx_dropped_inc(skb->dev);
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
return 0;
}
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 0392f6ba862b..25fd290082c4 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -389,8 +389,8 @@ static int ip6gre_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
struct tnl_ptk_info tpi;
struct ip6_tnl *t;
- if (gre_parse_header(skb, &tpi, NULL, htons(ETH_P_IPV6),
- offset) < 0)
+ if (gre_parse_header(skb, &tpi, true, htons(ETH_P_IPV6),
+ offset))
return -EINVAL;
ipv6h = (const struct ipv6hdr *)skb->data;
@@ -566,20 +566,19 @@ static int ip6erspan_rcv(struct sk_buff *skb,
static int gre_rcv(struct sk_buff *skb)
{
+ enum skb_drop_reason reason;
struct tnl_ptk_info tpi;
- bool csum_err = false;
- int hdr_len;
- hdr_len = gre_parse_header(skb, &tpi, &csum_err, htons(ETH_P_IPV6), 0);
- if (hdr_len < 0)
+ reason = gre_parse_header(skb, &tpi, false, htons(ETH_P_IPV6), 0);
+ if (reason)
goto drop;
- if (iptunnel_pull_header(skb, hdr_len, tpi.proto, false))
+ if (iptunnel_pull_header(skb, tpi.hdr_len, tpi.proto, false))
goto drop;
if (unlikely(tpi.proto == htons(ETH_P_ERSPAN) ||
tpi.proto == htons(ETH_P_ERSPAN2))) {
- if (ip6erspan_rcv(skb, &tpi, hdr_len) == PACKET_RCVD)
+ if (ip6erspan_rcv(skb, &tpi, tpi.hdr_len) == PACKET_RCVD)
return 0;
goto out;
}
@@ -590,8 +589,9 @@ static int gre_rcv(struct sk_buff *skb)
out:
icmpv6_send(skb, ICMPV6_DEST_UNREACH, ICMPV6_PORT_UNREACH, 0);
drop:
+ reason = reason ?: SKB_DROP_REASON_NOT_SPECIFIED;
dev_core_stats_rx_dropped_inc(skb->dev);
- kfree_skb(skb);
+ kfree_skb_reason(skb, reason);
return 0;
}
--
2.47.3
next prev parent reply other threads:[~2026-09-30 18:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-30 18:38 [PATCH net-next v5 00/14] tunnels: add core and gre drop reasons Anton Danilov
2026-09-30 18:38 ` [PATCH net-next v5 01/14] vxlan: rename the drop reasons for use by other tunnels Anton Danilov
2026-09-30 18:38 ` [PATCH net-next v5 02/14] ip_tunnel: make __iptunnel_pull_header() return a drop reason Anton Danilov
2026-09-30 18:38 ` [PATCH net-next v5 03/14] vxlan: report the drop reason of __iptunnel_pull_header() Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 04/14] ip_tunnel: add drop reasons to the generic RX path Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 05/14] ip6_tunnel: add drop reasons to the receive path Anton Danilov
2026-09-30 18:39 ` Anton Danilov [this message]
2026-09-30 18:39 ` [PATCH net-next v5 07/14] ip_gre: add drop reasons to the RX path Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 08/14] ip6_gre: " Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 09/14] ip_tunnel: add drop reasons to the transmit path Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 10/14] ip_gre: " Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 11/14] ip6_gre: make prepare_ip6gre_xmit_other() void Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 12/14] ip6_tunnel: make ip6_tnl_xmit() return a drop reason Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 13/14] ip6_gre: add drop reasons to the transmit path Anton Danilov
2026-09-30 18:39 ` [PATCH net-next v5 14/14] vxlan: report a circular route as SKB_DROP_REASON_RECURSION_LIMIT Anton Danilov
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