From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.216.49 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793811144; b=j4VPv1biSY42rIDYrfeDqN9js5yizufB0mGBpFUIbqPWddBGrUR/O4RMbTeGG+HrmrL7 O7a5jV5FpicDjXwi/fVJc0zMOmYBQfZO87x7Kh5o9vjbjG1ED1cfu7EhJqjKAH8JLnREw Vtgg1HjeH6WyQ4Iu/gHxseeb2hDzholRKVJJCWB0Wjid0kMrva5563qhFNa1ILmpM48AM nUTpehxHZckUfwOQayxvweJZxY79gc3pwOdcFMfAyAgPnHRUDkecpYxny4xS7foWj1gFi E/tQf2VWpW8LFYqHWWEta0FHi3/URJfDDt3L+Pqe4IWPnDgrN5UnFS0gvldMTPnXSdw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793811144; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Gm-Message-State:X-Gm-Gg:X-Received:Received:Mime-Version: Content-Transfer-Encoding:Content-Type:Date:Message-Id:Cc:Subject: From:To:X-Mailer:References:In-Reply-To; bh=mDQelrr4Kh/Jq4lqD8Bd1ygw8a8v5DRiulkfJQImUaA=; b=SwAr3elqSw7OxwT0WejGub80w74i7yDN3DLMdFEBxloTb+fT+Gysjfab+vjgFeo5qypR IxIHlECiaDu2T1B3bek9WMsspcncB0GAkiOiMnbGiY5sNxw23HLHNzw+FW75ZFKhSlwEf lZyvhmkU+phBdKqG6GQXTxXr4XIW0hCMJ9+IQ6aWtXBW6esSd7yBOVHoX/PXteT+VecmN +3GpEyUF7sW/GJlZbzboy+NsyQdmbw4/Ppgvuq2Sm3eCEsQBAvatwIOp6/lhEc43zhMmB frtiEzLmEk30860yCJnp4IHiIE94O6QeHz/o314WC6GaINeOn8wqmvPhFdix1lcXlTg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=kvAlMHA9; arc=none smtp.remote-ip=209.85.216.49 Received: from mail-pj1-f49.google.com (mail-pj1-f49.google.com [209.85.216.49]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5E895606D81E for ; Wed, 4 Nov 2026 16:52:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 5E895606D81E Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=kvAlMHA9 Received: by mail-pj1-f49.google.com with SMTP id 98e67ed59e1d1-3ada8bc2380so499515a91.3 for ; Wed, 04 Nov 2026 08:52:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1793811144; x=1794415944; darn=vger.kernel.org; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-type:content-transfer-encoding:mime-version:from:to:cc :subject:date:message-id:reply-to:content-type; bh=mDQelrr4Kh/Jq4lqD8Bd1ygw8a8v5DRiulkfJQImUaA=; b=kvAlMHA9YpLVp95q/S6+rfIKB0rxBFrfLZZgcxl9tkXcKRkQztUBTwOrAwv1bYnEZh qDB1aza7sd7sCkFjHBgbTr5ONi7xasnnWnCMi3ZChAbqAIz43AtJgQH3k5eE7vHhu81s a/gxOxiNC2yAXPRow31/dN3IIgNd3T99tw940mkHjn4kRm7FfmfUBHFenV0rEbEQyWQL FhiKhaB64QHMEzInvtZs2J9qRFs2LQzbdCgHc3iKCCKThQI3QIo4EmxmOra02M2gpiiQ rfTN9Xgt5EltN0laDIAcJhL3bE61iNfw35jRRqPFxcu2WlCzSTaKzJ7BnZOYk1NW8jyC 2NYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793811144; x=1794415944; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-type:content-transfer-encoding:mime-version:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=mDQelrr4Kh/Jq4lqD8Bd1ygw8a8v5DRiulkfJQImUaA=; b=hSQXwbwRBk4C1tizfl1ltwaLEOvrG6kLUevYVdyZxW+Aamtlajmg3LzW5xxO1hP7er oB1qV5YV/3x46HCl9GyGrJQ3h/f5uZuWx69vc0Z1YJqEcBcqfEqmpW59wTFlhVqcOi1r Sl+zqZgh8q1fBUbU0pVaak7cUdqNniDUr/GpoCWtXBBw6lusIHa10dMklSuqKdeUamtF iI9/3ZUuZoIXbXV8+jqrdOf1PVzXdei0YIq6ebkW4ejD3IbEa32Wogtk+XdeUNZ6OsKL 4f10yqLXzRedLxKLr7lBukR1GM1KQn+XjGVqbekbyxYxAiG+T9MPiNTwnZVhruyKpcw+ +kIw== X-Gm-Message-State: APuU4Z/L+rfAGkH2mxwYYqpAS4Sqsgj9oNBE7PuPyT+BO0sik8+YSvnL mRPlzUZO2nO5lUAyVVF5jx55jwNN+f2M4yR7G92WZ+r/MaILDaSLPbtbS3me9Q== X-Gm-Gg: AYBFou25Hc8GTSAtkc7wvTG03KbJzcIpHMGfzKxAhBc/KBTgTmTtSsYbGt3/O0Vd7C5 l8/59O9FfLPvDDXmHwIi30WM1t13UjJxCz+WE5jhQY8uqVRp/ZtrNkLcl+aNZCy7WMbB9yHJBen 9HSklPQ067jVTqhszZ1itiCsLAF+zJ5r69kNYojcbm/Tu/IL7pJZ2kgWD414gM1uuGkZjSvhKI5 Q88huN8CYxMPb9rAgAA3g2hoH2MLTuX361Fhn/+1qmU4x06W0zuOLjoQ0NuC2SJsmEk3sW4Du6a yf8d+8JXjIDMDghR5iPk2sqFnEX1sC1QwXO/t2chTQCaZ7oCHycWpB/gzQo1DyJrmn54/jj85nM RwJeDhSqs8UHQTVQon8IZ1t3VB6K5SwkXFrgRFhxLo71WWcECJ4+ukkoulGink3i9vu0yZODOXf uMemEfQ0NsaA4daob8ZspvupLON6RjcpziRsxESqn5/HBhcwR7/Or9C5qMmzEpe4GRNQvP66CPW t3ZPDFHeF6jmHVaReAF6Gu9FBKTNH/3DoI6FJECj0q0MD8sHo34MtBOL5Hxa+HwB8riMGE6gCnz ld+VcunHW7pbTB2059YHybMn/j6imgEcfuZtyIQOk7RXH/GdFLXPcEjRJM8qC+kvh/9Xnh/ek/s NlNX/fqJ6P4IVWMaLMvWNBPLnNaOqTzs8uA== X-Received: by 2002:a17:90a:fc4d:b0:3b0:ac2c:1619 with SMTP id 98e67ed59e1d1-3b0ac2c19c0mr685175a91.39.1793811143452; Wed, 04 Nov 2026 08:52:23 -0800 (PST) Received: from localhost ([153.61.198.252]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b09445a7f6sm4685568a91.6.2026.11.04.08.52.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Nov 2026 08:52:22 -0800 (PST) X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 04 Nov 2026 16:52:22 +0000 Message-Id: Cc: , "network dev" Subject: Re: [PATCH net] net: reject a negative TCP header offset in qdisc_pkt_len_segs_init() From: "Alexei Starovoitov" To: "Paolo Abeni" , X-Mailer: aerc 0.20.1-355-gf870624f6c37 References: <20261101194433.2637113-1-alexei.starovoitov@gmail.com> In-Reply-To: On Wed Nov 4, 2026 at 8:41 AM UTC, Paolo Abeni wrote: > On 11/2/26 23:46, Alexei Starovoitov wrote: >> On Mon, Nov 02, 2026 at 11:44 AM sashiko-bot@kernel.org wrote: >>>> + /* A header in front of skb->data gives a negative offset. */ >>>> + if ((int)hdr_len < 0 || >>>> + !pskb_may_pull(skb, hdr_len + sizeof(struct tcphdr))) >>>> return SKB_DROP_REASON_SKB_BAD_GSO; >>> >>> [Severity: High] >>> Should the (int)hdr_len < 0 check be placed immediately after hdr_len i= s >>> computed rather than only inside the SKB_GSO_TCPV4 | SKB_GSO_TCPV6 bran= ch? >>=20 >> No. It's already explained in the commit log. >>=20 >>> When (int)hdr_len < -8, hdr_len + sizeof(struct udphdr) wraps to an >>> unsigned int in [0x80000008, 0xffffffff] (> INT_MAX), which triggers >>> DEBUG_NET_WARN_ON_ONCE(len > INT_MAX) in >>> include/linux/skbuff.h:pskb_may_pull_reason() before returning >>> SKB_DROP_REASON_SKB_BAD_GSO. >>=20 >> Not a bug. That's CONFIG_DEBUG_NET only and the warn is right: >> the header is stale. >>=20 >>> Can this write uh->len (and uh->check in bnxt_sw_udp_gso_xmit() and >>> enetc_tso_hdr_csum()) before the start of the header buffer when >>> skb_transport_offset(skb) < -4? >>=20 >> No. The driver doesn't see this offset. >>=20 >>> Third, for other GSO types (such as SKB_GSO_FRAGLIST, SKB_GSO_UDP, >>> SKB_GSO_SCTP, or SKB_GSO_ESP), hdr_len remains 2^32 - |offset| at the e= nd >>> of qdisc_pkt_len_segs_init(): >>> >>> When (gso_segs - 1) * |offset| > skb->len, can qdisc_skb_cb(skb)->pkt_l= en >>> underflow in 32-bit unsigned arithmetic to ~4.29 GiB (exceeding >>> QDISC_PKT_LEN_MAX), causing deficit-based schedulers such as drr_dequeu= e() >>> and ets_dequeue() to spin in their deficit-refill loops? >>=20 >> No. > > FTR the nipa sashiko instance dismissed the above concerns autonomously: > > https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261101194433.263711= 3-1-alexei.starovoitov@gmail.com > > you can reasonably safely refer only to such instance when submitting > patches to net/net-next. Nice. I'll borrow your mechanism.