ipmr_cache_report() builds reports for mrouted from a packet that may be a synthetic RTM_GETROUTE query. That query skb stores the netlink requester portid in NETLINK_CB(), but the report is delivered to a raw IPv4 socket, whose receive path interprets skb->cb as IPCB(). Commit bb7403655b3c ("ipmr: support IP_PKTINFO on cache report IGMP msg") added IP_PKTINFO support by calling ipv4_pktinfo_prepare() on the original packet and then copying the entire 48-byte skb control block to the report skb. For synthetic route-query packets, this copies NETLINK_CB() bytes into IPCB() and lets a controlled portid corrupt IPCB(skb)->opt. With IP_RECVOPTS or IP_RETOPTS enabled, the raw socket receive path can then copy past the short report packet or overflow the stack option buffer. Keep the IP_PKTINFO support, but initialize the report skb control buffer and copy only the pktinfo fields prepared by ipv4_pktinfo_prepare(). Do this in the common path so both short reports and whole-packet reports are covered. This removes the accidental IP_RECVOPTS/IP_RETOPTS behavior on the mrouted socket, but that behavior was only a side effect of copying the entire control block and was never intended to work for these reports. Fixes: bb7403655b3c ("ipmr: support IP_PKTINFO on cache report IGMP msg") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zhiling Zou --- changes in v2: - reword the commit message to say the entire 48-byte skb control block is copied - mention that IP_RECVOPTS/IP_RETOPTS on the mrouted socket was never intended - move the pktinfo copy to the common path so both report branches are covered - v1 Link: https://lore.kernel.org/all/5bc7cd71c2d671b305f25497d88ae8a0aa663c08.1784894076.git.zhilinz@nebusec.ai/ net/ipv4/ipmr.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c index 1d9a4ac14fcef..4827973c6f9c0 100644 --- a/net/ipv4/ipmr.c +++ b/net/ipv4/ipmr.c @@ -1058,6 +1058,7 @@ static int ipmr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt, vifi_t vifi, int assert) { const int ihl = ip_hdrlen(pkt); + struct in_pktinfo *info; struct sock *mroute_sk; struct igmphdr *igmp; struct igmpmsg *msg; @@ -1112,8 +1113,6 @@ static int ipmr_cache_report(const struct mr_table *mrt, msg = (struct igmpmsg *)skb_network_header(skb); msg->im_vif = vifi; msg->im_vif_hi = vifi >> 8; - ipv4_pktinfo_prepare(mroute_sk, pkt, false); - memcpy(skb->cb, pkt->cb, sizeof(skb->cb)); /* Add our header. * Note that code, csum and group fields are cleared. */ @@ -1124,6 +1123,12 @@ static int ipmr_cache_report(const struct mr_table *mrt, skb->transport_header = skb->network_header; } + ipv4_pktinfo_prepare(mroute_sk, pkt, false); + memset(skb->cb, 0, sizeof(skb->cb)); + info = PKTINFO_SKB_CB(skb); + info->ipi_ifindex = PKTINFO_SKB_CB(pkt)->ipi_ifindex; + info->ipi_spec_dst = PKTINFO_SKB_CB(pkt)->ipi_spec_dst; + igmpmsg_netlink_event(mrt, skb); /* Deliver to mrouted */ -- 2.43.0