From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk1-f180.google.com (mail-qk1-f180.google.com [209.85.222.180]) (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 5377F3D8911 for ; Wed, 7 Oct 2026 17:36:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791394582; cv=none; b=F4HWd1AmmsIPqQSPkcXqzPf/mpb3QgfUs1/ZUpgQchgevD9DJ07bFR8bC5ryUjnU6n/eH+J/FuWyuKxMlpZct9aR/AkifkIPbVy6JzLKHez2up7Q84TmFTS81I5oZu9cN87Rs5aIyk/EDAeoM7cMZ7gwU1tzj1ZdIzUGD+3s8A4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791394582; c=relaxed/simple; bh=iWA6T1CpjWI8UxLZmS8SblObbmCsKvPQ75NFi5XaiB0=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=uUf+OHZdi7Z1BbFWdrVPehdkkgz0o2equ2pr1GXmYImOUSLzV1hkFDwV71Rl3pLN4nqP2r8AhcOxMzVM22DrKTF/f9hvMsulp2pYAl+yMewJp7QYU9iVcdLI6yYk5+ut880H9GzLTirTKyXOOOlTPTKUK6GZv7fXhkF3W7932as= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com; spf=pass smtp.mailfrom=toxicpanda.com; dkim=pass (2048-bit key) header.d=toxicpanda.com header.i=@toxicpanda.com header.b=PGRFNMFz; arc=none smtp.client-ip=209.85.222.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=toxicpanda.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=toxicpanda.com header.i=@toxicpanda.com header.b="PGRFNMFz" Received: by mail-qk1-f180.google.com with SMTP id af79cd13be357-93e027da24aso173081385a.3 for ; Wed, 07 Oct 2026 10:36:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=toxicpanda.com; s=google; t=1791394576; x=1791999376; darn=vger.kernel.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :content-type:mime-version:subject:date:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=nmeHgE/m1onXKnAwAH5DDKMXEgBrD3yqome89VS+iU4=; b=PGRFNMFzDDHXgF+JuzmS3BQks2K37dxnKTDgSE8KWItxXZGzLun6TvDcT9ZhjyVl84 xSZxh+QvryZrEJZujOZmrAvQs3UbhWYJM8UNNSkV/eQoLT0JiKQu+5Z0pd33+mOcKEwQ XrX5pP2TsrUvlBrzZuQsa7H+Iy+7GrZQAn8MJiZJuA/Bj0kNcfr4COfBBulSJ1Bj9HAM 2u4HqrOl1H2nV94epnphAyKX/23xNtrjCTzqoClb02J2eY9wzbL/bz4itO5pYwkTmOFM n1R1YzEZJTORSg7jkpzbS4wzziBjGEyKF4VGLPkyvJeirb0Z5MDPYsiIGWlKS5HtmOHa xz7g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791394576; x=1791999376; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :content-type:mime-version:subject:date:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=nmeHgE/m1onXKnAwAH5DDKMXEgBrD3yqome89VS+iU4=; b=0ZYFCK4LJVjKKBD+FNtrMPI55HCSrdZmzMS+W4m22PHY7g2eKutv1goc5c/avKTIgp LMelAsBjUlpqaXwbqsBby0ziKz0I0YQE8G+qbOWkVm/JX0CQqJ291NmAf0fB4MBZms99 GKQOPHi0G2LLaVx6j8ybjAiRM78Nq5O0Qm0p0ZvxC8jSmvIKV0DPLWOj9UKmVKjRXaRK uLRo3B21Mvf3AV2aFX3YhMV5t7W1yEoolYrOEh5gcbTkmwmWqG8yqOqJSWmSNjISwhA+ 7MFFZD0ygnAAr/2NSrfmb6i7oqYZkHUwcbTALV+A12JtwpaHOQBQn1UupgE8cJHkfo1M Ho7g== X-Forwarded-Encrypted: i=1; AKwUvBwFLNpxzjBK2kmwI3IPa5KQVl965OL2QeOJ0lqDBKNsJej1n/BfUu50tRzdbdBWdVa7O3kThqHI6EnGnKA=@vger.kernel.org X-Gm-Message-State: AFuF++nIbaiK8Sa5Ki4NUT5gFyj8rMtw8gqRS9y9pft+6PCySXVq+TuS T+y3vrXLqf3/RycptSEb042K5z1ABSKsYbRvk0zXlc2TcRaBLQruhrQTbOYDoO4giASScroeI29 1Wnj6M0A= X-Gm-Gg: AYBFou24kiwWt6vRdg2cy7+smCurh8si7HHAlrIiH0lnME4XI5jfIdNzG7WK6QXMFsM lFKvzgbZqY/TNAlduLRlGB3YRA0SVUVInYkdNtyI2azYIb/FDVcL5xwMOPLBIK/+uzByT1MJOBs KLxV9pyHQpkCr2G1jSEs/WlIHuSWT/RVx2IBBfXEvkllmxI92hBdge84wPMgp782cc/O8O/h3/8 gxMocQjcZmlnGL9ojQcogRAnEJTsfsPaGyzKLGh6KmgZsP7PjdvXL+27KG5BqwolVZrij+lqyuA GxnfwkaOE7jnO+I2O5luyBt5uLdBMylCyCAa5SXqNk8Bwwn13uBi//qp65r49/l8uvm5jGBHDnW wPq8VGeylxyHgEmVkDfMN5qHqa9/1PLZCasOgHNaGrxyRpzwz8WEd7kO4tQFACrRXb+rREikOgr 7vgbWncC6T0AmlqQFlwFLXN55wx7KmXywK+U0axnH6uGc8dcCynzHb44Vt2IQS0UWh53YYKl6Av 8DZoTlc0Yn5eBc= X-Received: by 2002:a05:620a:1a0a:b0:93e:66e6:fa4 with SMTP id af79cd13be357-93e9b72e5b1mr557833185a.16.1791394576316; Wed, 07 Oct 2026 10:36:16 -0700 (PDT) Received: from toxicpanda.com ([153.61.196.243]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93e991e9e5csm261941485a.37.2026.10.07.10.36.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2026 10:36:15 -0700 (PDT) From: Josef Bacik Date: Wed, 07 Oct 2026 17:36:01 +0000 Subject: [PATCH net-next v2 2/8] net: skbuff: don't BUG() on a bad frag_list layout in skb_segment() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261007-b4-skbuff-bug-on-v2-2-b9a5f732895b@toxicpanda.com> References: <20261007-b4-skbuff-bug-on-v2-0-b9a5f732895b@toxicpanda.com> In-Reply-To: <20261007-b4-skbuff-bug-on-v2-0-b9a5f732895b@toxicpanda.com> To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Josef Bacik X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openssh-sha256; t=1791394570; l=2697; i=josef@toxicpanda.com; h=from:subject:message-id; bh=iWA6T1CpjWI8UxLZmS8SblObbmCsKvPQ75NFi5XaiB0=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgUBr36M/n0nWN0DNbnxwzIiCZez6MG JiruuNaSCI/zXsAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QFi3QIvWhd2Mxhv3Aen91UpvjyXdXR8IZmFpsWcV/heEJdJkDndaF965IV19Tq4zgj0euoLfffo UnGoNh1cN9wQ= X-Developer-Key: i=josef@toxicpanda.com; a=openssh; fpr=SHA256:C8kOX2QUJCMqnCX+KEeoqRAjLo9L+ELOSH2NSAJHqGA skb_segment()'s frag_list walk assumes the GRO-shaped layout it expects and BUG()s when the layout doesn't match. Anybody who can get a malformed GSO skb to a segmentation point gets to crash the box. Most recently commit d5dc1e69fd72 ("inet: frags: strip GSO state from fragments before reassembly") fixed one that an unprivileged user could trigger with two writes to a tap device in their own user namespace. commit 3382a1ed7f77 ("net: fix udp gso skb_segment after pull from frag_list") fixed another. skb_segment() already has an error path for a bad layout: the too-many-frags check sets -EINVAL and frees the partial segment list. Take that path for the four layout checks, with a DEBUG_NET_WARN_ON_ONCE() for debug kernels. The packet gets dropped, which is what should happen to a packet we can't segment. The one check that runs after skb_clone() and before the clone is linked into the segment list frees the clone itself. Assisted-by: LLM Signed-off-by: Josef Bacik --- net/core/skbuff.c | 25 +++++++++++++++++++++---- 1 file changed, 21 insertions(+), 4 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index d226fe77d484..a6821ab13969 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4916,7 +4916,11 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) && (skb_headlen(list_skb) == len || sg)) { - BUG_ON(skb_headlen(list_skb) > len); + if (unlikely(skb_headlen(list_skb) > len)) { + DEBUG_NET_WARN_ON_ONCE(1); + err = -EINVAL; + goto err; + } nskb = skb_clone(list_skb, GFP_ATOMIC); if (unlikely(!nskb)) @@ -4929,7 +4933,12 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, pos += skb_headlen(list_skb); while (pos < offset + len) { - BUG_ON(i >= nfrags); + if (unlikely(i >= nfrags)) { + DEBUG_NET_WARN_ON_ONCE(1); + kfree_skb(nskb); + err = -EINVAL; + goto err; + } size = skb_frag_size(frag); if (pos + size > offset + len) @@ -5036,9 +5045,17 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_shinfo(nskb)->flags |= skb_shinfo(frag_skb)->flags & SKBFL_SHARED_FRAG; if (!skb_headlen(list_skb)) { - BUG_ON(!nfrags); + if (unlikely(!nfrags)) { + DEBUG_NET_WARN_ON_ONCE(1); + err = -EINVAL; + goto err; + } } else { - BUG_ON(!list_skb->head_frag); + if (unlikely(!list_skb->head_frag)) { + DEBUG_NET_WARN_ON_ONCE(1); + err = -EINVAL; + goto err; + } /* to make room for head_frag. */ i--; -- 2.55.0