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Mon, 24 Aug 2020 20:49:26 +0000 Received: from gmail.com (unknown [104.132.1.76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 195B02067C; Mon, 24 Aug 2020 20:49:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598302154; bh=PDF5FB3f/iX6KmB9XrlWFrnk42OQsjSRBtJ1FLkbKmk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jUh/EXYBZSsJDdmVjLNI9Ide1YTidVvRvP57Wf4SyWXTEaa/Oq3Sun1fEYKw2zPbo aKCpyYiHp520+hjmEuKybQsRGqMfFfEWdJnjuX5r1U5Kobvoccm1Wqv2sA2JRBKfsY /d8CDZHgd3G1/Lq1Dw0aWx5EI4uNe9CYC6tcvDpQ= Date: Mon, 24 Aug 2020 13:49:12 -0700 From: Eric Biggers To: Jeff Layton Message-ID: <20200824204912.GD1650861@gmail.com> References: <20200824061712.195654-1-ebiggers@kernel.org> <20200824061712.195654-2-ebiggers@kernel.org> <0cf5638796e7cddacc38dcd1e967368b99f0069a.camel@kernel.org> <20200824182114.GB1650861@gmail.com> <06a7d9562b84354eb72bd67c9d4b7262dac53457.camel@kernel.org> <20200824190221.GC1650861@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Headers-End: 1kAJPA-005a6r-He Subject: Re: [f2fs-dev] [RFC PATCH 1/8] fscrypt: add fscrypt_prepare_new_inode() and fscrypt_set_context() X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fscrypt@vger.kernel.org, linux-ext4@vger.kernel.org, linux-mtd@lists.infradead.org, ceph-devel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Mon, Aug 24, 2020 at 03:42:59PM -0400, Jeff Layton wrote: > On Mon, 2020-08-24 at 12:02 -0700, Eric Biggers wrote: > > On Mon, Aug 24, 2020 at 02:47:07PM -0400, Jeff Layton wrote: > > > On Mon, 2020-08-24 at 11:21 -0700, Eric Biggers wrote: > > > > On Mon, Aug 24, 2020 at 12:48:48PM -0400, Jeff Layton wrote: > > > > > > +void fscrypt_hash_inode_number(struct fscrypt_info *ci, > > > > > > + const struct fscrypt_master_key *mk) > > > > > > +{ > > > > > > + WARN_ON(ci->ci_inode->i_ino == 0); > > > > > > + WARN_ON(!mk->mk_ino_hash_key_initialized); > > > > > > + > > > > > > + ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino, > > > > > > + &mk->mk_ino_hash_key); > > > > > > > > > > i_ino is an unsigned long. Will this produce a consistent results on > > > > > arches with 32 and 64 bit long values? I think it'd be nice to ensure > > > > > that we can access an encrypted directory created on a 32-bit host from > > > > > (e.g.) a 64-bit host. > > > > > > > > The result is the same regardless of word size and endianness. > > > > siphash_1u64(v, k) is equivalent to: > > > > > > > > __le64 x = cpu_to_le64(v); > > > > siphash(&x, 8, k); > > > > > > > > > > In the case where you have an (on-storage) inode number that is larger > > > than 2^32, x will almost certainly be different on a 32 vs. 64-bit > > > wordsize. > > > > > > On the box with the 32-bit wordsize, you'll end up promoting i_ino to a > > > 64-bit word and the upper 32 bits will be zeroed out. So it seems like > > > this means that if you're using inline hardware you're going to end up > > > with a result that won't work correctly across different wordsizes. > > > > That's only possible if the VFS is truncating the inode number, which would also > > break userspace in lots of ways like making applications think that files are > > hard-linked together when they aren't. Also, IV_INO_LBLK_64 would break. > > > > The correct fix for that would be to make inode::i_ino 64-bit. > > > > ...or just ask the filesystem for the 64-bit inode number via ->getattr > or a new op. You could also just truncate it down to 32 bits or xor the > top and bottom bits together first, etc... > > > Note that ext4 and f2fs (currently the only filesystems that support the > > IV_INO_LBLK_* flags) only support 32-bit inode numbers. > > > > Ahh, ok. That explains why it's not been an issue so far. Still, if > you're reworking this code anyway, you might want to consider avoiding > i_ino here. Let's just enforce ino_bits <= 32 for IV_INO_LBLK_32 for now, like is done for IV_INO_LBLK_64: https://lkml.kernel.org/r/20200824203841.1707847-1-ebiggers@kernel.org There's no need to add extra complexity for something that no one wants yet. (And as mentioned, this won't prevent ceph or other filesystems with 64-bit inode numbers from adding support for fscrypt, as IV_INO_LBLK_32 support is optional and has a pretty specific use case.) - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel