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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , Jamal Hadi Salim , Jiri Pirko , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, zjamg , stable@vger.kernel.org Subject: [PATCH 1/2] net: fix OOB read in qdisc_pkt_len_segs_init() on negative transport offset Date: Thu, 17 Sep 2026 20:21:52 +0800 Message-ID: <20260917122153.62722-2-ndaugoing@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260917122153.62722-1-ndaugoing@gmail.com> References: <20260917122153.62722-1-ndaugoing@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In qdisc_pkt_len_segs_init(), the header length up to the transport layer is computed via skb_transport_offset() or skb_inner_transport_offset(): /* mac layer + network layer */ if (!skb->encapsulation) { if (unlikely(!skb_transport_header_was_set(skb))) return SKB_NOT_DROPPED_YET; hdr_len =3D skb_transport_offset(skb); } else { hdr_len =3D skb_inner_transport_offset(skb); } Both offset accessors return a signed int, but hdr_len is declared as unsigned int. If a packet undergoes header operations (such as skb_vlan_untag() pulling stacked VLAN tags without updating inner_transport_header, or other header stripping that advances skb->data past the transport header), the offset becomes negative. When stored into unsigned int hdr_len, negative values are converted to large positive numbers near UINT_MAX (e.g. (unsigned int)-16 is 0xFFFFFFF0). Subsequently: 1. pskb_may_pull(skb, hdr_len + sizeof(struct tcphdr)) evaluates 0xFFFFFFF0 + 20, which overflows 32-bit unsigned arithmetic to 4. Since the packet length exceeds 4 bytes, pskb_may_pull() returns true, bypassing the bounds check. 2. th =3D (const struct tcphdr *)(skb->data + hdr_len) zero-extends hdr_len on 64-bit architectures, creating a wild pointer pointing ~4 GiB past skb->data into unmapped memory. 3. __tcp_hdrlen(th) dereferences th->doff, triggering an immediate kernel crash (page fault / KASAN wild-memory-access panic). A similar unsigned overflow occurs for UDP (SKB_GSO_UDP_L4). Fix this by declaring hdr_len as int to match the return types of skb_transport_offset() and skb_inner_transport_offset(), and explicitly rejecting negative offsets by returning SKB_DROP_REASON_SKB_BAD_GSO. Fixes: 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()") Cc: stable@vger.kernel.org Signed-off-by: zjamg --- net/core/dev.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index ecfbd72d5d1a..f2dbf99181ec 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4159,8 +4159,9 @@ EXPORT_SYMBOL_GPL(validate_xmit_skb_list); static enum skb_drop_reason qdisc_pkt_len_segs_init(struct sk_buff *skb) { struct skb_shared_info *shinfo =3D skb_shinfo(skb); - unsigned int hdr_len, tlen; + unsigned int tlen; u16 gso_segs; + int hdr_len; =20 qdisc_skb_cb(skb)->pkt_len =3D skb->len; if (!shinfo->gso_size) { @@ -4182,6 +4183,8 @@ static enum skb_drop_reason qdisc_pkt_len_segs_init(s= truct sk_buff *skb) } else { hdr_len =3D skb_inner_transport_offset(skb); } + if (unlikely(hdr_len < 0)) + return SKB_DROP_REASON_SKB_BAD_GSO; /* + transport layer */ if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) { const struct tcphdr *th; --=20 2.53.0 From nobody Fri Sep 25 02:42:23 2026 Received: from mail-pj2-f12.google.com (mail-pj2-f12.google.com [74.125.227.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8C8054CDA3A for ; 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Thu, 17 Sep 2026 05:22:19 -0700 (PDT) Received: from localhost.localdomain ([183.194.144.114]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33bf5a6a175sm16360661eec.9.2026.09.17.05.22.14 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 17 Sep 2026 05:22:18 -0700 (PDT) From: zjamg To: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , Jamal Hadi Salim , Jiri Pirko , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, zjamg , stable@vger.kernel.org Subject: [PATCH 2/2] net/sched: sch_cake: check negative transport offset in cake_overhead() Date: Thu, 17 Sep 2026 20:21:53 +0800 Message-ID: <20260917122153.62722-3-ndaugoing@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260917122153.62722-1-ndaugoing@gmail.com> References: <20260917122153.62722-1-ndaugoing@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In cake_overhead(), the header length up to the transport layer is computed using logic borrowed from qdisc_pkt_len_segs_init(): /* borrowed from qdisc_pkt_len_segs_init() */ if (!skb->encapsulation) hdr_len =3D skb_transport_offset(skb); else hdr_len =3D skb_inner_transport_offset(skb); Both skb_transport_offset() and skb_inner_transport_offset() return a signed int, but hdr_len is declared as unsigned int. If an encapsulated or stripped packet has a negative transport offset, hdr_len is converted to a huge positive integer near UINT_MAX. When passed to skb_header_pointer(skb, hdr_len, ...), the signed offset argument in skb_header_pointer() becomes negative, which can lead to an out-of-bounds pointer (skb->data + negative_offset) and an OOB read. Fix this by declaring hdr_len as int and falling back to the standard cake_calc_overhead() calculation if hdr_len is negative. Fixes: a41851bea7bf ("net: account for encap headers in qdisc pkt len") Cc: stable@vger.kernel.org Signed-off-by: zjamg --- net/sched/sch_cake.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c index dc93267029e7..ce9e85f9571e 100644 --- a/net/sched/sch_cake.c +++ b/net/sched/sch_cake.c @@ -1413,10 +1413,11 @@ static u32 cake_calc_overhead(struct cake_sched_dat= a *qd, u32 len, u32 off) static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *= skb) { const struct skb_shared_info *shinfo =3D skb_shinfo(skb); - unsigned int hdr_len, last_len =3D 0; + unsigned int last_len =3D 0; u32 off =3D skb_network_offset(skb); u16 segs =3D qdisc_pkt_segs(skb); u32 len =3D qdisc_pkt_len(skb); + int hdr_len; =20 WRITE_ONCE(q->avg_netoff, cake_ewma(q->avg_netoff, off << 16, 8)); =20 @@ -1429,6 +1430,9 @@ static u32 cake_overhead(struct cake_sched_data *q, c= onst struct sk_buff *skb) else hdr_len =3D skb_inner_transport_offset(skb); =20 + if (unlikely(hdr_len < 0)) + return cake_calc_overhead(q, len, off); + /* + transport layer */ if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) { --=20 2.53.0