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([2a0d:3344:2712:7e10:4d59:d956:544f:d65c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce5cfe74sm21829187f8f.35.2025.10.14.00.32.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Oct 2025 00:32:10 -0700 (PDT) Message-ID: Date: Tue, 14 Oct 2025 09:32:09 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] udp: drop secpath before storing an skb in a receive queue To: Sabrina Dubroca , Eric Dumazet Cc: "David S . Miller" , Jakub Kicinski , Simon Horman , Willem de Bruijn , netdev@vger.kernel.org, eric.dumazet@gmail.com, Michal Kubecek References: <20251014060454.1841122-1-edumazet@google.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/14/25 8:37 AM, Sabrina Dubroca wrote: > 2025-10-14, 06:04:54 +0000, Eric Dumazet wrote: >> Michal reported and bisected an issue after recent adoption >> of skb_attempt_defer_free() in UDP. >> >> We had the same issue for TCP, that Sabrina fixed in commit 9b6412e6979f >> ("tcp: drop secpath at the same time as we currently drop dst") > > I'm not convinced this is the same bug. The TCP one was a "leaked" > reference (delayed put). This looks more like a double put/missing > hold to me (we get to the destroy path without having done the proper > delete, which would set XFRM_STATE_DEAD). > > And this shouldn't be an issue after b441cf3f8c4b ("xfrm: delete > x->tunnel as we delete x"). I think Sabrina is right. If the skb carries a secpath, UDP_SKB_IS_STATELESS is not set, and skb_release_head_state() will be called by skb_consume_udp(). skb_ext_put() does not clear skb->extensions nor ext->refcnt, if skb_attempt_defer_free() enters the slow path (kfree_skb_napi_cache()), the skb will go through again skb_release_head_state(), with a double free. I think something alike the following (completely untested) should work: --- diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 95241093b7f0..4a308fd6aa6c 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1851,8 +1851,10 @@ void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len) sk_peek_offset_bwd(sk, len); if (!skb_shared(skb)) { - if (unlikely(udp_skb_has_head_state(skb))) + if (unlikely(udp_skb_has_head_state(skb))) { skb_release_head_state(skb); + skb->active_extensions = 0; + } skb_attempt_defer_free(skb); return; } ---