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[209.132.180.67]) by mx.google.com with ESMTP id o8si19603620pll.391.2019.04.16.16.00.02; Tue, 16 Apr 2019 16:00:18 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=LtKypqkZ; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730883AbfDPW7K (ORCPT + 99 others); Tue, 16 Apr 2019 18:59:10 -0400 Received: from mail-vs1-f54.google.com ([209.85.217.54]:36451 "EHLO mail-vs1-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730844AbfDPW7J (ORCPT ); Tue, 16 Apr 2019 18:59:09 -0400 Received: by mail-vs1-f54.google.com with SMTP id n4so12540692vsm.3 for ; Tue, 16 Apr 2019 15:59:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=PkKooqQ06/x99Omqb2YZsUWOnyhQfZoAkUghY8lDlLM=; b=LtKypqkZz/Avmq/R7FBhrtR/OhkkC2OJxwlOgGAjNNo4ApmgDl1OwAm9oIC94WGDI8 mDLa1uLy8HP4RD0i+4P2bs11eWBqmIGbwEMrJYiDvjrIIaCzEBgmGHAxLCsai1i7Hx/+ BsncVnyzke5GqRZNvq81Amhgn9Sm+LGezJrTNdyKR+IdIS7uiCJniUdf8nEYEcYPp+jf hy00cmcfvojmuOIn5QgvSukslKGNbeLBgSCHVSGCcSx+MUC9Iwab1SLagdtK+g7liMg6 4pSwyX2cm48P6SKPY237YQKCHqV2TPjxooIs84waCtJmdSACfemUSYQbfLgzaZmNBm/C x3qw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PkKooqQ06/x99Omqb2YZsUWOnyhQfZoAkUghY8lDlLM=; b=JJR2DhbyFDLEERqUkJ0YyYBXEiuwNvTLXdiMaJYsXy1UpjNYQ54vvfImdPJ9s4IN7w sbTnqR4KY9J93odtnWBh3afqxR0XkjgUsFeAd4m1J26mWq1SOudL6waW3npWwbD3Y52l WYzxTKjDPJBWUMq39k80jmfUf8PT4AtDdYO+YW8NnAkQWvvYuV5v6YIukNzC/x4DaOaO prxrrlrVUR6RoMwUZanT3YelWRzcUbEbeG98f1mgDS2DchCtZCkCByZZN5fDFWX0/55P 3/N+ZFqA0hXgmIVsBqoUiP6ypt5T5a443xyDWah42ePvbWNNe81Qus2MHgp3h7czlANU sWyw== X-Gm-Message-State: APjAAAXNAVtcODuanS0OZ0W3Ygq0oB+VFenlWh6CKQ5BAsQDDPBvTWiq mfX/yIRWNHZkBmi9TnEjvOtBwU8X25W7TtHctAuzM8fJ X-Received: by 2002:a67:f04e:: with SMTP id q14mr47183774vsm.133.1555455547820; Tue, 16 Apr 2019 15:59:07 -0700 (PDT) MIME-Version: 1.0 References: <40a6486d-2dba-5574-06da-3e0ebb25f2b1@iogearbox.net> In-Reply-To: <40a6486d-2dba-5574-06da-3e0ebb25f2b1@iogearbox.net> From: Kees Cook Date: Tue, 16 Apr 2019 17:58:56 -0500 Message-ID: Subject: Re: BPF RNG To: Daniel Borkmann Cc: Hannes Frederic Sowa , LKML , Ingo Molnar , "Reshetova, Elena" , Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 16, 2019 at 10:13 AM Daniel Borkmann wrote: > > On 04/16/2019 03:55 PM, Kees Cook wrote: > > [correcting Alexei's email address and resending...] > > > > On Tue, Apr 16, 2019 at 8:54 AM Kees Cook wrote: > >> > >> Hi, > >> > >> In looking at prandom_u32() users, I noticed that BPF uses its own > >> state variable with bpf_user_rnd_u32(). It appears that this state is > > Correct, we split that off from the main one. > > >> never reseeded like regular prandom_u32(). (See __prandom_timer().) Is > >> this intentional, or should reseeding be happening? > > The prng is not to be used in any security-critical context. That said, > we optionally could perform reseeding from time to time, though that > should probably be done generically, so that all "external" > prandom_u32_state() users could register themselves upon init whether > they opt-in for periodic reseeding or not. Yeah, it seemed like it should be built into the API. I'll add this to the TODO list. ;) Thanks for double-checking. -- Kees Cook