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Message-ID: <5fbeecfc311ea182aa1d1c771725ab8b4cac515e.1729778144.git.benoit.monin@gmx.fr>
Date: Thu, 24 Oct 2024 16:01:54 +0200
From: Benoît Monin <benoit.monin@....fr>
To: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Jiri Pirko <jiri@...nulli.us>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Lorenzo Bianconi <lorenzo@...nel.org>
Cc: netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
Benoît Monin <benoit.monin@....fr>
Subject: [PATCH v2 net] net: skip offload for NETIF_F_IPV6_CSUM if ipv6 header contains extension
As documented in skbuff.h, devices with NETIF_F_IPV6_CSUM capability
can only checksum TCP and UDP over IPv6 if the IP header does not
contains extension.
This is enforced for UDP packets emitted from user-space to an IPv6
address as they go through ip6_make_skb(), which calls
__ip6_append_data() where a check is done on the header size before
setting CHECKSUM_PARTIAL.
But the introduction of UDP encapsulation with fou6 added a code-path
where it is possible to get an skb with a partial UDP checksum and an
IPv6 header with extension:
* fou6 adds a UDP header with a partial checksum if the inner packet
does not contains a valid checksum.
* ip6_tunnel adds an IPv6 header with a destination option extension
header if encap_limit is non-zero (the default value is 4).
The thread linked below describes in more details how to reproduce the
problem with GRE-in-UDP tunnel.
Add a check on the network header size in skb_csum_hwoffload_help() to
make sure no IPv6 packet with extension header is handed to a network
device with NETIF_F_IPV6_CSUM capability.
Link: https://lore.kernel.org/netdev/26548921.1r3eYUQgxm@benoit.monin/T/#u
Fixes: aa3463d65e7b ("fou: Add encap ops for IPv6 tunnels")
Signed-off-by: Benoît Monin <benoit.monin@....fr>
---
changelog
* v2:
- patch against net instead of net-next
- clarify documentation of NETIF_F_IPV6_CSUM
- add link to thread describing the problem
- add fixes tag
- use vlan_get_protocol to check for IPv6
* v1:
- https://lore.kernel.org/netdev/0dc0c2af98e96b1df20bd36aeaed4eb4e27d507e.1728056028.git.benoit.monin@gmx.fr/T/#u
---
net/core/dev.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/net/core/dev.c b/net/core/dev.c
index ea5fbcd133ae..8453e14d301b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3639,6 +3639,9 @@ int skb_csum_hwoffload_help(struct sk_buff *skb,
return 0;
if (features & (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM)) {
+ if (vlan_get_protocol(skb) == htons(ETH_P_IPV6) &&
+ skb_network_header_len(skb) != sizeof(struct ipv6hdr))
+ goto sw_checksum;
switch (skb->csum_offset) {
case offsetof(struct tcphdr, check):
case offsetof(struct udphdr, check):
@@ -3646,6 +3649,7 @@ int skb_csum_hwoffload_help(struct sk_buff *skb,
}
}
+sw_checksum:
return skb_checksum_help(skb);
}
EXPORT_SYMBOL(skb_csum_hwoffload_help);
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