From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f177.google.com (mail-yw1-f177.google.com [209.85.128.177]) (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 815453BFE24 for ; Thu, 26 Mar 2026 16:25:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774542320; cv=none; b=QmMK53+3eoP4uAGHXeEIJi7vW32QtA0yFM+9fUWn3raeYiKXdk/zJUQXd1igowDRUbz5mU4VhiXr2pHa/90VOX7Yib4i/T9YlkZvQSkipiCt9iVX96qP5oIl7cjlOVHbEkP3f64qJxEwlCSSReMujdrtVLm4q0O9D9GVxMwKFqM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774542320; c=relaxed/simple; bh=VWZT9ERgK7gJqphC8GoSZLKrh7DUq8FCawjcEwvjBu0=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: Mime-Version:Content-Type; b=txmMZH/u/YqFRi6ia8N/6LTSLq44n6SY5WlTl0DmvNwBYfvWf+QJXlkxUqA18m159nCfQIxHY9WP2Ae7Pmf6gzm9H6uZIrZUmToAGPrKOucLmDzU7s1zOvpBJnv5BuHj49ct7PvtTl7AqDQF/IiFwYTyfoPWSTAFpPvb7f1qcWw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=cFEuLlDY; arc=none smtp.client-ip=209.85.128.177 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) header.d=gmail.com header.i=@gmail.com header.b="cFEuLlDY" Received: by mail-yw1-f177.google.com with SMTP id 00721157ae682-79ac5de41d8so11946697b3.3 for ; Thu, 26 Mar 2026 09:25:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1774542317; x=1775147117; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=tQ+dnIdkTMUfClaOEhsfhfSTdn6XkHf1UrfOW0f1rdo=; b=cFEuLlDYiqOY9JEQ6/zyK8ZSOh1kJeIuv2z7QFb5Jx59pw6SQtvWZRGV0imOCB0uiv UVzWI1+UR5sKSaCdrq6vDSQko1IulVC66ntAL8w/vcCXpLDkO0T4JvvEMwoH10WByQ5F 9bpOWAfmAC24AB3b1T59Rh0dNR1xJw77hZhK8FlqO0yY5dLKCBGjMf3JLZveqBnAJA+W uHF1LCjN2qlWl3nmD7GfSNn/LyQFbzN7pjPT+S4UcNrBH27p+CEKsas6a1Hui7YsuBig z/VkZV6FDX4XZJ3OGTQ4rEd1Qw+1bOzkO6H6a5JLaYKjrCpDMhQSktGDE/EqxPLRbx2i sKuQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774542317; x=1775147117; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:x-gm-gg:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=tQ+dnIdkTMUfClaOEhsfhfSTdn6XkHf1UrfOW0f1rdo=; b=egErEyuOrys5f+dLaATYuhkBWrdi1DNUTx5BdDlCCYMV91rlhkaPDt1XWQ+tcPR2mu HcO7tliTJgQ3j1iKf67IcA9sSAaZVyqtoHTDQrRVJWJP5VjoIwI07byqYqEhPVknrD3I zM+pPuEwVxrfdh5LbCzWcmh/9FgiBYP1d3N8rXMW3tQ/9MDkaMiUIyTOJ0kJvwwM+WnM f85mHRazGbCYTcwAGVbv261OV9tXHKrcu+LFW/JAv8YJJzvFDCguapnGMhxQdOm4S+MS zQ0etzpICnMyLAjc35ERlSuXsUdBgmc+XsLow1gMfbY/TotrJYNVv7xml5NfVR1FanIJ cFaA== X-Forwarded-Encrypted: i=1; AJvYcCXL85fj3gQNndQXkaJhCHUYmJ0wQg0Lc1Skr1rWN+wvt5TEoCOJEr/OeH9rntXd3EWvfAHdT1k=@vger.kernel.org X-Gm-Message-State: AOJu0YzANUCZdV0B4GLihDqZT+iMNAHqRx9Dclzdb9D72Hzlyhip7z/M DYNuQ2//JtQLQWB+fGmYhp4aI2qkkUOArL1irdMPuKlwF7vb7m0+VepU X-Gm-Gg: ATEYQzzNAqo2XkZWUQQ2fRaacZnB1SUB1EKQjVfwcHnECt5HzTdrZO/yvMjpfDCK+H5 sUiuu3MH4i+yMrzZVfFsv4n4ACXNNktYore4UIvcOp9ETyyoaVpHH/csLUZBYwhkF/78q6Hfqc2 asMeazt05E2yRb5O/UVJZ4ijjXx5IJfiSVCUtYA7lbqcSikO0dnKrZUJdV57YJAN9ZNQqpVoI7A 9hfPx2QvZQL8hN1yqgdxuP1aQUelneSg9S0ZRN0WTwWsTYI11yGp3vPAhRKNTjufW6xEsoEURtg ymQwH0OxeodeVObZ0fHj7lhMVftK18hxvr8v0i4N8HAWtYDi8NDz4ZTzEGrCzHNMmfFdeEkwdjl dYB1nDhv9cmRwTL7p41eq6FEMHA/PfVy8iQZIXL95RfRe/kPaTLkvp4Cih7c/mWpIevxaKjElOz erdg2SLL9/aMmorhfP7P4D8zTCyYD/aGw1vYFbXY+ZNU1PgranEgGUdRG4lYrIW/vJ03EDquz3d 7b2 X-Received: by 2002:a05:690c:f09:b0:79a:d2ba:3c28 with SMTP id 00721157ae682-79ad2ba4245mr68382447b3.43.1774542317200; Thu, 26 Mar 2026 09:25:17 -0700 (PDT) Received: from gmail.com (180.134.85.34.bc.googleusercontent.com. [34.85.134.180]) by smtp.gmail.com with UTF8SMTPSA id 00721157ae682-79b1e45254bsm14981827b3.48.2026.03.26.09.25.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 09:25:16 -0700 (PDT) Date: Thu, 26 Mar 2026 12:25:13 -0400 From: Willem de Bruijn To: Guoyu Su , edumazet@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com Cc: willemdebruijn.kernel@gmail.com, netdev@vger.kernel.org, horms@kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot+1543a7d954d9c6d00407@syzkaller.appspotmail.com, Guoyu Su Message-ID: In-Reply-To: <20260326121813.457049-1-yss2813483011xxl@gmail.com> References: <20260326121813.457049-1-yss2813483011xxl@gmail.com> Subject: Re: [PATCH net v6] net: use skb_header_pointer() for TCPv4 GSO frag_off Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Guoyu Su wrote: > Syzbot reported a KMSAN uninit-value warning in gso_features_check() > called from netif_skb_features() [1]. > > gso_features_check() reads iph->frag_off to decide whether to clear > mangleid_features. Accessing the IPv4 header via ip_hdr()/inner_ip_hdr() > can rely on skb header offsets that are not always safe for direct > dereference on packets injected from PF_PACKET paths. > > Use skb_header_pointer() for the TCPv4 frag_off check so the header read > is robust whether data is already linear or needs copying. > > This also removes the SKB_GSO_DODGY special casing: skb_header_pointer() > already fast-paths linear data, so a separate direct-access path is not > needed. Does not belong in the commit message. It's a diff vs the previous version. > [1] https://syzkaller.appspot.com/bug?extid=1543a7d954d9c6d00407 > > Link: https://lore.kernel.org/netdev/willemdebruijn.kernel.1a9f35039caab@gmail.com/ > Fixes: cbc53e08a793 ("GSO: Add GSO type for fixed IPv4 ID") > Reported-by: syzbot+1543a7d954d9c6d00407@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=1543a7d954d9c6d00407 > Tested-by: syzbot+1543a7d954d9c6d00407@syzkaller.appspotmail.com > Signed-off-by: Guoyu Su > --- > v6: > - Use skb_header_pointer() for both DODGY and non-DODGY TCPv4 GSO > packets in gso_features_check(). > - Drop the SKB_GSO_DODGY special-casing for IPv4 header access. > > v5: https://lore.kernel.org/netdev/20260320141459.9691-1-yss2813483011xxl@gmail.com/ > v4: https://lore.kernel.org/netdev/20260319005421.14908-1-yss2813483011xxl@gmail.com/ > v3: https://lore.kernel.org/netdev/20260312104351.185370-1-yss2813483011xxl@gmail.com/ > v2: https://lore.kernel.org/netdev/20260308083319.1255118-1-yss2813483011xxl@gmail.com/ > v1: https://lore.kernel.org/netdev/20260307162905.3697050-1-yss2813483011xxl@gmail.com/ > > net/core/dev.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/net/core/dev.c b/net/core/dev.c > index 14a83f2035b9..8a15ca67cfed 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -3805,10 +3805,16 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb, > * segmentation-offloads.rst). > */ > if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4) { > - struct iphdr *iph = skb->encapsulation ? > - inner_ip_hdr(skb) : ip_hdr(skb); > + const struct iphdr *iph; > + struct iphdr _iph; > > - if (!(iph->frag_off & htons(IP_DF))) minor: no whitespace in the middle of the variable definition block. > + int nhoff = skb->encapsulation ? > + skb_inner_network_offset(skb) : > + skb_network_offset(skb); > + > + iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph); > + > + if (!iph || !(iph->frag_off & htons(IP_DF))) > features &= ~dev->mangleid_features; > } > > -- > 2.34.1 >