From 439f392084f8f7f59ab9d47a9579185accefe1d8 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 10 Sep 2026 20:46:12 +0000 Subject: [PATCH] drop_monitor: fix out-of-bounds write in reset_per_cpu_data() In reset_per_cpu_data(), al is computed as: al = sizeof(struct net_dm_alert_msg); al += dm_hit_limit * sizeof(struct net_dm_drop_point); al += sizeof(struct nlattr); skb = genlmsg_new(al, GFP_KERNEL); ... nla = nla_reserve(skb, NLA_UNSPEC, sizeof(struct net_dm_alert_msg)); ... msg = nla_data(nla); memset(msg, 0, al); Because al includes sizeof(struct nlattr) (the 4-byte attribute header), genlmsg_new() allocates al bytes of tailroom starting at nla. However, msg points to nla_data(nla), which is located sizeof(struct nlattr) bytes past nla. Calling memset(msg, 0, al) therefore writes al bytes starting from msg, exceeding the allocated buffer by sizeof(struct nlattr) (4 bytes) and corrupting skb_shared_info. Fix this by letting al represent only the payload length, allocating the skb with genlmsg_new(nla_total_size(al), GFP_KERNEL), and zeroing al bytes from msg. Fixes: 683703a26e46 ("drop_monitor: Update netlink protocol to include netlink attribute header in alert message") Signed-off-by: Eric Dumazet Reviewed-by: Hangbin Liu Link: https://patch.msgid.link/20260910204612.3762015-5-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/core/drop_monitor.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c index 795c15dd1771..edc660778408 100644 --- a/net/core/drop_monitor.c +++ b/net/core/drop_monitor.c @@ -141,9 +141,8 @@ static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data) al = sizeof(struct net_dm_alert_msg); al += dm_hit_limit * sizeof(struct net_dm_drop_point); - al += sizeof(struct nlattr); - skb = genlmsg_new(al, GFP_KERNEL); + skb = genlmsg_new(nla_total_size(al), GFP_KERNEL); if (!skb) goto err;