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From: David Laight <David.Laight@ACULAB.COM>
To: 'Kees Cook' <keescook@chromium.org>,
	Scott Branden <scott.branden@broadcom.com>
Cc: Mimi Zohar <zohar@linux.ibm.com>,
	Matthew Wilcox <willy@infradead.org>,
	James Morris <jmorris@namei.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jessica Yu <jeyu@kernel.org>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Casey Schaufler <casey@schaufler-ca.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Matthew Garrett <matthewgarrett@google.com>,
	David Howells <dhowells@redhat.com>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	KP Singh <kpsingh@google.com>, Dave Olsthoorn <dave@bewaar.me>,
	Hans de Goede <hdegoede@redhat.com>,
	Peter Jones <pjones@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Stephen Boyd <stephen.boyd@linaro.org>,
	Paul Moore <paul@paul-moore.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 07/13] fs/kernel_read_file: Switch buffer size arg to size_t
Date: Mon, 20 Jul 2020 08:34:32 +0000
Message-ID: <5db582d3ec08401eb4731ce3acd51561@AcuMS.aculab.com> (raw)
In-Reply-To: <20200717174309.1164575-8-keescook@chromium.org>

From: Kees Cook
> Sent: 17 July 2020 18:43
> In preparation for further refactoring of kernel_read_file*(), rename
> the "max_size" argument to the more accurate "buf_size", and correct
> its type to size_t. Add kerndoc to explain the specifics of how the
> arguments will be used. Note that with buf_size now size_t, it can no
> longer be negative (and was never called with a negative value). Adjust
> callers to use it as a "maximum size" when *buf is NULL.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  fs/kernel_read_file.c            | 34 +++++++++++++++++++++++---------
>  include/linux/kernel_read_file.h |  8 ++++----
>  security/integrity/digsig.c      |  2 +-
>  security/integrity/ima/ima_fs.c  |  2 +-
>  4 files changed, 31 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
> index dc28a8def597..e21a76001fff 100644
> --- a/fs/kernel_read_file.c
> +++ b/fs/kernel_read_file.c
> @@ -5,15 +5,31 @@
>  #include <linux/security.h>
>  #include <linux/vmalloc.h>
> 
> +/**
> + * kernel_read_file() - read file contents into a kernel buffer
> + *
> + * @file	file to read from
> + * @buf		pointer to a "void *" buffer for reading into (if
> + *		*@buf is NULL, a buffer will be allocated, and
> + *		@buf_size will be ignored)
> + * @buf_size	size of buf, if already allocated. If @buf not
> + *		allocated, this is the largest size to allocate.
> + * @id		the kernel_read_file_id identifying the type of
> + *		file contents being read (for LSMs to examine)
> + *
> + * Returns number of bytes read (no single read will be bigger
> + * than INT_MAX), or negative on error.
> + *
> + */

That seems to be self-inconsistent.
If '*buf' is NULL is both says that buf_size is ignored and
is treated as a limit.
To make life easier, zero should probably be treated as no-limit.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 17:42 [PATCH 00/13] Introduce partial kernel_read_file() support Kees Cook
2020-07-17 17:42 ` [PATCH 01/13] firmware_loader: EFI firmware loader must handle pre-allocated buffer Kees Cook
2020-07-17 19:08   ` Scott Branden
2020-07-17 17:42 ` [PATCH 02/13] fs/kernel_read_file: Remove FIRMWARE_PREALLOC_BUFFER enum Kees Cook
2020-07-17 19:09   ` Scott Branden
2020-07-17 17:42 ` [PATCH 03/13] fs/kernel_read_file: Remove FIRMWARE_EFI_EMBEDDED enum Kees Cook
2020-07-17 19:10   ` Scott Branden
2020-07-17 17:42 ` [PATCH 04/13] fs/kernel_read_file: Split into separate include file Kees Cook
2020-07-17 17:43 ` [PATCH 05/13] fs/kernel_read_file: Split into separate source file Kees Cook
2020-07-17 19:11   ` Scott Branden
2020-07-17 17:43 ` [PATCH 06/13] fs/kernel_read_file: Remove redundant size argument Kees Cook
2020-07-17 19:04   ` Scott Branden
2020-07-17 19:55     ` Scott Branden
2020-07-17 22:06     ` Kees Cook
2020-07-18  5:44       ` Scott Branden
2020-07-21 21:43   ` Scott Branden
2020-07-21 21:50     ` Kees Cook
2020-07-17 17:43 ` [PATCH 07/13] fs/kernel_read_file: Switch buffer size arg to size_t Kees Cook
2020-07-20  8:34   ` David Laight [this message]
2020-07-17 17:43 ` [PATCH 08/13] fs/kernel_read_file: Add file_size output argument Kees Cook
2020-07-17 17:43 ` [PATCH 09/13] LSM: Introduce kernel_post_load_data() hook Kees Cook
2020-07-17 17:43 ` [PATCH 10/13] firmware_loader: Use security_post_load_data() Kees Cook
2020-07-17 17:43 ` [PATCH 11/13] module: Call security_kernel_post_load_data() Kees Cook
2020-07-17 17:43 ` [PATCH 12/13] LSM: Add "contents" flag to kernel_read_file hook Kees Cook
2020-07-17 17:43 ` [PATCH 13/13] fs/kernel_file_read: Add "offset" arg for partial reads Kees Cook
2020-07-17 19:17 ` [PATCH 00/13] Introduce partial kernel_read_file() support Scott Branden
2020-07-17 22:10   ` Kees Cook

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