From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f193.google.com (mail-pl1-f193.google.com [209.85.214.193]) (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 D30223DBD4D for ; Mon, 1 Jun 2026 15:18:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.193 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780327146; cv=none; b=OMf/dxe0pD7/bEXV+KWUiHa1jfUJ90feW+/qGUbQf+zVhCKwoElRxbBttT9nadiNlTTNgYy2T8ZBm/dBpfssBjGjAS7mOAejXV+gAQ5zKEIWtaxOSM2t+BOAim4c5SC3i9ZkWajLKBlrBlY+Tddr9bYmxG92ByAcR6q7mEAvGQc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780327146; c=relaxed/simple; bh=PQO0UZwXLLelrITKmhXhC6F0znNCjfRA0kOIy5ZvCNU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WrnQSgHl8prQUpxIyoiyQ8+BSgw/8Fb7cl2OZS95Z20avktyVAbpkA1tVNKxaYo66gu3g5WKdSrfkAq1o3MB+DJb+6muyqDP0TjNVS7MEcFOQIp2JMN04b/qABwkk9KL8hYzDPG0kk84JWekfIw2PVVVg8DJCa6lr7oYvcf63fo= 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=gr4tGw/Q; arc=none smtp.client-ip=209.85.214.193 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="gr4tGw/Q" Received: by mail-pl1-f193.google.com with SMTP id d9443c01a7336-2c0c2a68d01so9886235ad.1 for ; Mon, 01 Jun 2026 08:18:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1780327139; x=1780931939; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=aDR/0d6767AKXu4Gbp+1FbUsOAvR4r8bVucFSVBkYL8=; b=gr4tGw/Q/FhooWcObcw2/szyDWZ8wkK15lcn36CakQOjov5TyO7oxkusGhs6mV28P2 aQF0CjvkygHGfktnoQHH1oXFfKN454R8r7FWVdv07qtQlPbVu3/BYzmHLg11AwElZeEh /Fl45gYCucHNJFgwYHWvS1+tGN26C/6n/BGrihc7LCThEIFhA95T2e542MQg0nfDyQQ+ geWuEeu052TH5vZFxUdlUxlYO2OnqhvGINOpJYVBJ8SE6VNf23euGXSo560TRRQGfh3/ nbwFNu1JZEe+rI4yio0SVgxyJYkvSyIszcwV8yK2zuUFVn4fekcgjLT5sP3u1OLu9Lai OEYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780327139; x=1780931939; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=aDR/0d6767AKXu4Gbp+1FbUsOAvR4r8bVucFSVBkYL8=; b=ZD3EgMMv5xbLVG0Kb2gAUyaxybBlnQis8CmydiFypXYzIsdjYPE0CdrTVUz4ivxB4X 9UnVaYMET4I1SsRAGLZP+NhFVIXcpVzgm84Gl50hshrJA/zYsxR8hlzB1BTEXU/s7eW4 oxPMs/+A7Qa0NwO0RkV3dMDrnVxAeSDwNi+Xpn/6PtCHBvZ+K/l/Q5JONcYm/UqqxtTC vNSk7KAob5I2CnMFUZMUH8GVYAW9MsGyqdZ28K15u/xj+yDHoulXJly2bDEoOhC4sOM+ B33kHvhe5hfNdtW103bQaFGZtvNMvahGQlkn1+WmPxJ2ZufSk4bjyX21yVx7PGQAB4JT nXgA== X-Forwarded-Encrypted: i=1; AFNElJ+vQQ1E5QFoT1mHFEu6APCOWU3+czye2kYOgZRGDhwMdJ3HoffvtLhiaVd+mhi8SHPTQJE=@vger.kernel.org X-Gm-Message-State: AOJu0Yy3GGC9Us2rg3R4lq/gXwmHvcwIgDlSegY3kNLZx54d5VAg+FNx 2LSJ5Fq3KdbWJsQazxU+ODxEg111f0+5COh96Iuna614lAS2kQ9jJ44t X-Gm-Gg: Acq92OGPjWYqKUj2CgYmf9YeSQdh3F9OCdN/6rwI0gTzq+nr8Po88h5ybWARxsoAM0I 7p5vaniaX1kCRPvexZBLSNzSx0HOjBDgeGSKKVaPwrZAYVqxzZK9J62Wu2aC494YCFo9hXye/ui 07pjmxQbxMxmk8XM9QxuoVuU9lr+MahQgWD74rwukn4+5HKoLwCRwFtVQbIPs3ByUZsWH/gK0d1 OKdT8qy2MKhl086+AAELUVhPdVGTok6yHlZoQeRg4KWjcxxZ32Jmu3I+BziRthbrU5pZ+HRsydc s0SnJd6LcN5Py1kCSoDaogkf8lMkV+hVMskaz/MbFSxD3qllzi1zNNs0SErONjV4DxmOZP+eCMj JmwcSJD2bQasH0CCq61dpHRoZ0oO8wfi1fnWFiyF/UhG5ETNnOEOu9WaRFPm19TTMP5hhkuFJNk L/oFSEsYxJfZgpUsNeRMQA5HnYwLc= X-Received: by 2002:a17:902:e54c:b0:2bf:2b84:c207 with SMTP id d9443c01a7336-2bf3688e46emr142931175ad.35.1780327138899; Mon, 01 Jun 2026 08:18:58 -0700 (PDT) Received: from localhost ([2a03:2880:2ff:50::]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2bf23b01732sm113263525ad.54.2026.06.01.08.18.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Jun 2026 08:18:58 -0700 (PDT) Date: Mon, 1 Jun 2026 08:18:57 -0700 From: Stanislav Fomichev To: Jason Xing Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, sdf@fomichev.me, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, horms@kernel.org, andrew+netdev@lunn.ch, bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing Subject: Re: [PATCH net v5] xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata() Message-ID: References: <20260530042630.80626-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260530042630.80626-1-kerneljasonxing@gmail.com> On 05/30, Jason Xing wrote: > From: Jason Xing > > The TX metadata area resides in the UMEM buffer which is memory-mapped > and concurrently writable by userspace. In xsk_skb_metadata(), > csum_start and csum_offset are read from shared memory for bounds > validation, then read again for skb assignment. A malicious userspace > application can race to overwrite these values between the two reads, > bypassing the bounds check and causing out-of-bounds memory access > during checksum computation in the transmit path. > > Fix this by reading csum_start and csum_offset into local variables > once, then using the local copies for both validation and assignment. > > Note that other metadata fields (flags, launch_time) and the cached > csum fields may be mutually inconsistent due to concurrent userspace > writes, but this is benign: the only security-critical invariant is > that each field's validated value is the same one used, which local > caching guarantees. > > Closes: https://lore.kernel.org/all/20260503200927.73EA1C2BCB4@smtp.kernel.org/ > Fixes: 48eb03dd2630 ("xsk: Add TX timestamp and TX checksum offload support") > Reviewed-by: Maciej Fijalkowski > Signed-off-by: Jason Xing Acked-by: Stanislav Fomichev