From 199271ebc71c1e0913b2fad988a7bff330a8828a Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Tue, 1 Sep 2026 22:57:14 +0300 Subject: [PATCH] net: ipv6: Clamp to IP6_MAX_MTU in ip6_dst_mtu_maybe_forward Commit 427faee167bc ("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 ac6627a28dbf ("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: 427faee167bc ("net: ipv6: introduce ip6_dst_mtu_maybe_forward") Signed-off-by: Alice Mikityanska Suggested-by: Willem de Bruijn Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260901195714.673548-5-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- include/net/ip6_route.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h index c69f1c871922..b9e8d2b759e9 100644 --- a/include/net/ip6_route.h +++ b/include/net/ip6_route.h @@ -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); }