From 16e408e607a94b646fb14a2a98422c6877ae4b3c Mon Sep 17 00:00:00 2001 From: Yizhou Zhao Date: Wed, 27 May 2026 16:31:58 +0800 Subject: [PATCH] net: garp: fix unsigned integer underflow in garp_pdu_parse_attr The receive-side GARP attribute parser computes dlen with reversed operands: dlen = sizeof(*ga) - ga->len; ga->len is the on-wire attribute length and includes the GARP attribute header. For normal attributes with data, ga->len is larger than sizeof(*ga), so the subtraction underflows in unsigned arithmetic. The resulting value is later passed to garp_attr_lookup(), whose length argument is u8. After truncation, the parsed data length usually no longer matches the length stored for locally registered attributes, so received Join/Leave events are ignored. This breaks the GARP receive path for common attributes, such as GVRP VLAN registration attributes. Compute the data length as the attribute length minus the header length. Fixes: eca9ebac651f ("net: Add GARP applicant-only participant") Reported-by: Yizhou Zhao Reported-by: Yuxiang Yang Reported-by: Ao Wang Reported-by: Xuewei Feng Reported-by: Qi Li Reported-by: Ke Xu Signed-off-by: Yizhou Zhao Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260527083200.42861-1-zhaoyz24@mails.tsinghua.edu.cn Signed-off-by: Jakub Kicinski --- net/802/garp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/802/garp.c b/net/802/garp.c index 6f563b6797d9..c7a39f298ad6 100644 --- a/net/802/garp.c +++ b/net/802/garp.c @@ -453,7 +453,7 @@ static int garp_pdu_parse_attr(struct garp_applicant *app, struct sk_buff *skb, if (!pskb_may_pull(skb, ga->len)) return -1; skb_pull(skb, ga->len); - dlen = sizeof(*ga) - ga->len; + dlen = ga->len - sizeof(*ga); if (attrtype > app->app->maxattr) return 0;