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([73.140.210.38]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84553829252sm928782b3a.48.2026.06.18.21.53.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Jun 2026 21:53:54 -0700 (PDT) From: xmei5@asu.edu To: dsahern@kernel.org, idosch@nvidia.com, netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, kuba@kernel.org, horms@kernel.org, bestswngs@gmail.com, Xiang Mei Subject: [PATCH net] ipv6: Fix null-ptr-deref in fib6_nh_mtu_change(). Date: Thu, 18 Jun 2026 21:53:34 -0700 Message-ID: <20260619045334.2427073-1-xmei5@asu.edu> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Xiang Mei fib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg->dev) and dereferences idev->cnf.mtu6 without a NULL check. addrconf_ifdown() clears dev->ip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has released tb6_lock, so the RA-driven MTU walk can observe a NULL idev and oops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(), but this re-fetch is unguarded; nexthop-backed routes survive addrconf_ifdown()'s flush, so the walk still reaches it after ip6_ptr is nulled. Return 0 when idev is NULL, matching rt6_mtu_change_route() and the fib6_mtu() fix in commit 5ad509c1fdad ("ipv6: Fix null-ptr-deref in fib6_mtu()."). Oops: general protection fault, ... KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af] RIP: 0010:fib6_nh_mtu_change+0x203/0x990 rt6_mtu_change_route+0x141/0x1d0 __fib6_clean_all+0xd0/0x160 rt6_mtu_change+0xb4/0x100 ndisc_router_discovery+0x24b5/0x2cb0 icmpv6_rcv+0x12e9/0x1710 ipv6_rcv+0x39b/0x410 Fixes: c0b220cf7d80 ("ipv6: Refactor exception functions") Reported-by: Weiming Shi Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Xiang Mei --- net/ipv6/route.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 6361ad2fcf77..a1301334da48 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -5055,6 +5055,9 @@ static int fib6_nh_mtu_change(struct fib6_nh *nh, void *_arg) struct inet6_dev *idev = __in6_dev_get(arg->dev); u32 mtu = f6i->fib6_pmtu; + if (!idev) + return 0; + if (mtu >= arg->mtu || (mtu < arg->mtu && mtu == idev->cnf.mtu6)) fib6_metric_set(f6i, RTAX_MTU, arg->mtu); -- 2.43.0