linux-ext4 - Re: [PATCH v4 05/16] fs-verity: add Kconfig and the helper functions for hashing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190615125731.GF6142@mit.edu>
Date:   Sat, 15 Jun 2019 08:57:31 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-integrity@...r.kernel.org, Jaegeuk Kim <jaegeuk@...nel.org>,
        Victor Hsieh <victorhsieh@...gle.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v4 05/16] fs-verity: add Kconfig and the helper functions
 for hashing

On Thu, Jun 06, 2019 at 08:51:54AM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Add the beginnings of the fs/verity/ support layer, including the
> Kconfig option and various helper functions for hashing.  To start, only
> SHA-256 is supported, but other hash algorithms can easily be added.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Looks good; you can add:

Reviewed-off-by: Theodore Ts'o <tytso@....edu>

One thought for consideration below...


> +
> +/*
> + * Maximum depth of the Merkle tree.  Up to 64 levels are theoretically possible
> + * with a very small block size, but we'd like to limit stack usage during
> + * verification, and in practice this is plenty.  E.g., with SHA-256 and 4K
> + * blocks, a file with size UINT64_MAX bytes needs just 8 levels.
> + */
> +#define FS_VERITY_MAX_LEVELS		16

Maybe we should make FS_VERITY_MAX_LEVELS 8 for now?  This is an
implementation-level restriction, and currently we don't support any
architectures that have a page size < 4k.  We can always bump this
number up in the future if it ever becomes necessary, and limiting max
levels to 8 saves almost 100 bytes of stack space in verify_page().

						- Ted