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ip6_gre: remove obsolete ERSPAN PMTU update

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A tc tunnel_key action can attach a METADATA_IP_TUNNEL dst to an skb,
and mirred can redirect it to a native ip6erspan device. The legacy PMTU
update in ip6erspan_tunnel_xmit() treats that metadata dst as a route.
Since it has no output device, dst_dev(dst)->mtu dereferences NULL.

On v7.2 with KASAN, an initial UID/GID 65534 process with CapEff 0 used
self-created user and network namespaces to trigger:

  KASAN: null-ptr-deref
  RIP: ip6erspan_tunnel_xmit+0x10fc/0x2cc0
  Kernel panic - not syncing: Fatal exception in interrupt

The update is obsolete. Commit fe1a4ca0a2 ("ip6_gre: process toobig
in a better way") changed IPv6 GRE Too Big handling to update the
underlay route and removed the equivalent block from __gre6_xmit().
ip6_tnl_xmit() then propagates the underlay PMTU to the overlay route.

Remove the stale ERSPAN copy and its now-unused dst variable. This
eliminates the metadata-dst dereference and keeps ERSPAN aligned with
IPv6 GRE PMTU handling.

Fixes: 5a963eb61b ("ip6_gre: Add ERSPAN native tunnel support")
Cc: stable@vger.kernel.org
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20261002033058.358137-1-4ncienth@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Daehyeon Ko 2026-10-02 12:30:58 +09:00 committed by Jakub Kicinski
parent ab699d296e
commit 8bc60db48e
1 changed files with 0 additions and 7 deletions
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7
net/ipv6/ip6_gre.c
View File

@ -923,7 +923,6 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
{
struct ip_tunnel_info *tun_info = NULL;
struct ip6_tnl *t = netdev_priv(dev);
struct dst_entry *dst = skb_dst(skb);
IP_TUNNEL_DECLARE_FLAGS(flags) = { };
bool truncate = false;
int encap_limit = -1;
@ -1058,12 +1057,6 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
gre_build_header(skb, 8, flags, proto, 0,
htonl(atomic_fetch_inc(&t->o_seqno)));
/* TooBig packet may have updated dst->dev's mtu */
if (!t->parms.collect_md && dst) {
mtu = READ_ONCE(dst_dev(dst)->mtu);
if (dst_mtu(dst) > mtu)
dst->ops->update_pmtu(dst, NULL, skb, mtu, false);
}
err = ip6_tnl_xmit(skb, dev, dsfield, &fl6, encap_limit, &mtu,
NEXTHDR_GRE);
if (err != 0) {