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net: ipv6: Clamp to IP6_MAX_MTU in ip6_dst_mtu_maybe_forward

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Commit 427faee167 ("net: ipv6: introduce ip6_dst_mtu_maybe_forward")
dropped the IP6_MAX_MTU clamp that used to be present in ip6_mtu(). A
similar IPv4 commit ac6627a28d ("net: ipv4: Consolidate ipv4_mtu and
ip_dst_mtu_maybe_forward") preserves the IP_MAX_MTU clamp.

Restore the upper bound in the IPv6 flow to avoid potential 16-bit
overflows in forwarding paths.

Fixes: 427faee167 ("net: ipv6: introduce ip6_dst_mtu_maybe_forward")
Signed-off-by: Alice Mikityanska <alice@isovalent.com>
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260901195714.673548-5-alice.kernel@fastmail.im
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Alice Mikityanska 2026-09-01 22:57:14 +03:00 committed by Jakub Kicinski
parent 18a9a43421
commit 199271ebc7
1 changed files with 2 additions and 0 deletions
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2
include/net/ip6_route.h
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@ -384,6 +384,8 @@ static inline unsigned int ip6_dst_mtu_maybe_forward(const struct dst_entry *dst
rcu_read_unlock();
out:
mtu = min_t(unsigned int, mtu, IP6_MAX_MTU);
return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
}