6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 235b42b5860189eb8c27c36435ad932cae65a734 ] IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU. When an ingress multicast packet misses MFC lookup, ip6mr_cache_unresolved() places the skb onto the unresolved queue, escaping the receive-side RCU grace period. If the underlying route is deleted and freed, and the MFC queue is later resolved with a wrong parent interface, ip6_mr_forward() invokes ip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab use-after-free. Report packets queued to mroute6_sk (a raw socket) and netlink notifications do not require an attached dst entry. Fix this by: 1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs do not hold a dst. 2. Dropping skb_dst before queuing unresolved skbs in ip6mr_cache_unresolved(), matching the fact that multicast forwarding resolves outgoing routes anew via ip6_route_output(). Fixes: 67f415dd2906 ("ipv6: convert rx data path to not take refcnt on dst") Reported-by: Zero Day Initiative Signed-off-by: Eric Dumazet Reviewed-by: Hangbin Liu Link: https://patch.msgid.link/20260818172755.4083692-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/ip6mr.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c index ac0120b75ff2b..d95b988be4afe 100644 --- a/net/ipv6/ip6mr.c +++ b/net/ipv6/ip6mr.c @@ -1128,7 +1128,6 @@ static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt, msg->im6_src = ipv6_hdr(pkt)->saddr; msg->im6_dst = ipv6_hdr(pkt)->daddr; - skb_dst_set(skb, dst_clone(skb_dst(pkt))); skb->ip_summed = CHECKSUM_UNNECESSARY; } @@ -1138,6 +1137,7 @@ static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt, return -EINVAL; } + skb_dst_drop(skb); mrt6msg_netlink_event(mrt, skb); /* Deliver to user space multicast routing algorithms */ @@ -1217,6 +1217,7 @@ static int ip6mr_cache_unresolved(struct mr_table *mrt, mifi_t mifi, skb->dev = dev; skb->skb_iif = dev->ifindex; } + skb_dst_drop(skb); skb_queue_tail(&c->_c.mfc_un.unres.unresolved, skb); err = 0; } -- 2.53.0