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Miller" , Eric Dumazet , Paolo Abeni Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, tgopinath@linux.microsoft.com, kys@microsoft.com, "Xiang Mei (Microsoft)" Subject: [PATCH net] amt: refresh cached IP header pointers after MLD/IGMP checks Date: Fri, 10 Jul 2026 01:41:09 +0000 Message-ID: <20260710014109.536177-1-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 amt_dev_xmit() and amt_update_handler() cache iph/ip6h before calling ip_mc_check_igmp() / ipv6_mc_check_mld(), which may pskb_may_pull() a non-linear skb and reallocate skb->head. The stale pointers are then read (amt_dev_xmit: group.ip{4,6} = iph/ip6h->daddr; amt_update_handler: ip{,v6}_eth_mc_map()), a slab-use-after-free. tx is reachable by an unprivileged user whose amt device has SG enabled; rx by a tunnel peer sending a membership update fragmented across several IP fragments. Reload iph/ip6h after the check returns, like commit f0e42f0c4337 ("ipv6: sit: reload inner IPv6 header after GSO offloads"). tx path: BUG: KASAN: slab-use-after-free in amt_dev_xmit (drivers/net/amt.c:1238) Read of size 16 by task exploit amt_dev_xmit (drivers/net/amt.c:1238) dev_hard_start_xmit (net/core/dev.c:3905) __dev_queue_xmit (net/core/dev.c:4872) packet_sendmsg (net/packet/af_packet.c:3114) rx path: BUG: KASAN: slab-use-after-free in amt_rcv (drivers/net/amt.c:2530) Read of size 4 by task exploit amt_rcv (drivers/net/amt.c:2530) udp_queue_rcv_one_skb (net/ipv4/udp.c:2388) ip_local_deliver (net/ipv4/ip_input.c:262) ip_rcv (net/ipv4/ip_input.c:612) Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface") Fixes: bc54e49c140b ("amt: add multicast(IGMP) report message handler") Fixes: b75f7095d4d4 ("amt: add mld report message handler") Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Xiang Mei (Microsoft) --- drivers/net/amt.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/amt.c b/drivers/net/amt.c index 951dd10e192b..8bc61c539b0a 100644 --- a/drivers/net/amt.c +++ b/drivers/net/amt.c @@ -1210,6 +1210,7 @@ static netdev_tx_t amt_dev_xmit(struct sk_buff *skb, struct net_device *dev) } else { data = true; } + iph = ip_hdr(skb); v6 = false; group.ip4 = iph->daddr; #if IS_ENABLED(CONFIG_IPV6) @@ -1234,6 +1235,7 @@ static netdev_tx_t amt_dev_xmit(struct sk_buff *skb, struct net_device *dev) } else { data = true; } + ip6h = ipv6_hdr(skb); v6 = true; group.ip6 = ip6h->daddr; #endif @@ -2498,6 +2500,7 @@ static bool amt_update_handler(struct amt_dev *amt, struct sk_buff *skb) netdev_dbg(amt->dev, "Invalid IGMP\n"); return true; } + iph = ip_hdr(skb); spin_lock_bh(&tunnel->lock); amt_igmp_report_handler(amt, skb, tunnel); @@ -2517,6 +2520,7 @@ static bool amt_update_handler(struct amt_dev *amt, struct sk_buff *skb) netdev_dbg(amt->dev, "Invalid MLD\n"); return true; } + ip6h = ipv6_hdr(skb); spin_lock_bh(&tunnel->lock); amt_mld_report_handler(amt, skb, tunnel); -- 2.43.0