From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga02.intel.com ([134.134.136.20]:53153 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750743Ab2J3BuB (ORCPT ); Mon, 29 Oct 2012 21:50:01 -0400 Message-ID: <1351561798.7817.352.camel@yhuang-dev> Subject: Re: [PATCH 2/9] uuid: use random32_get_bytes() From: Huang Ying To: "Theodore Ts'o" Cc: Akinobu Mita , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, chris.mason@fusionio.com, linux-btrfs@vger.kernel.org Date: Tue, 30 Oct 2012 09:49:58 +0800 In-Reply-To: <20121029205200.GD7098@thunk.org> References: <1351408746-8623-1-git-send-email-akinobu.mita@gmail.com> <1351408746-8623-2-git-send-email-akinobu.mita@gmail.com> <20121029205200.GD7098@thunk.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Mon, 2012-10-29 at 16:52 -0400, Theodore Ts'o wrote: > On Sun, Oct 28, 2012 at 04:18:59PM +0900, Akinobu Mita wrote: > > Use random32_get_bytes() to generate 16 bytes of pseudo-random bytes. > > > > Signed-off-by: Akinobu Mita > > Since your patch is going to allow users to set the random seed, it > means that what had previously been a bad security bug has just become > a grievous security bug. If you are going to be generating UUID's > they _must_ use a truly random random generator, since the whole point > of uuid's is that they be unique. If someone can trivially set the > random seed of a prng, and thus cause the uuid generator to generate, > well, non-unique UUID's, the results can range anywhere from > confusion, to file system corruption and data loss. > > Fortunately, there is only one user of lib/uuid.c, and that's the > btrfs file system. > > Chris and the Btrfs folks --- my recommendation would be to ditch the > use of uuid_be_gen, "git rm lib/uuid.c" with extreme prejudice, and > use generate_random_uuid() which was coded over a decade ago in > drivers/char/random.c. Not only does this properly use the kernel > random number generator, but it also creates a UUID with the correct > format. (It's not enough to set the UUID version to 4; you also need > to set the UUID variant to be DCE if you want to be properly compliant > with RFC 4122 --- see section 4.1.1.) The uuid_le/be_gen() in lib/uuid.c has set UUID variants to be DCE, that is done in __uuid_gen_common() with "b[8] = (b[8] & 0x3F) | 0x80". To deal with random number generation issue, how about use get_random_bytes() in __uuid_gen_common()? > The btrfs file system doesn't generate uuid's in any critical fast > paths as near as I can determine, so it should be perfectly safe to > use uuid_generate() --- I also would drop the whole distinction > between little-endian and big-endian uuid's, BTW. RFC 4122 is quite > explicit about how uuid's should be encoded, and it's in internet byte > order. This is what OSF/DCE uses, and it's what the rest of the world > (Microsoft, SAP AG, Apple, GNOME, KDE) uses as well. uuid_be complies RFC4122, it uses internet byte order. But EFI uses little endian. Best Regards, Huang Ying