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From: Johannes Berg <johannes@sipsolutions.net>
To: Kees Cook <keescook@chromium.org>,
	"Gustavo A . R . Silva" <gustavoars@kernel.org>
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Subject: Re: [PATCH 02/32] Introduce flexible array struct memcpy() helpers
Date: Wed, 04 May 2022 09:25:56 +0200	[thread overview]
Message-ID: <d3b73d80f66325fdfaf2d1f00ea97ab3db03146a.camel@sipsolutions.net> (raw)
In-Reply-To: <20220504014440.3697851-3-keescook@chromium.org>

On Tue, 2022-05-03 at 18:44 -0700, Kees Cook wrote:
> 
> For example, using the most complicated helper, mem_to_flex_dup():
> 
>     /* Flexible array struct with members identified. */
>     struct something {
>         int mode;
>         DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(int, how_many);
>         unsigned long flags;
>         DECLARE_FLEX_ARRAY_ELEMENTS(u32, value);

In many cases, the order of the elements doesn't really matter, so maybe
it'd be nicer to be able to write it as something like

DECLARE_FLEX_STRUCT(something,
	int mode;
	unsigned long flags;
	,
	int, how_many,
	u32, value);

perhaps? OK, that doesn't seem so nice either.

Maybe

struct something {
	int mode;
	unsigned long flags;
	FLEX_ARRAY(
		int, how_many,
		u32, value
	);
};

or so? The long and duplicated DECLARE_FLEX_ARRAY_ELEMENTS_COUNT and
DECLARE_FLEX_ARRAY_ELEMENTS seems a bit tedious to me, at least in cases
where the struct layout is not the most important thing (or it's already
at the end anyway).


>     struct something *instance = NULL;
>     int rc;
> 
>     rc = mem_to_flex_dup(&instance, byte_array, count, GFP_KERNEL);
>     if (rc)
>         return rc;

This seems rather awkward, having to set it to NULL, then checking rc
(and possibly needing a separate variable for it), etc.

But I can understand how you arrived at this:
 - need to pass instance or &instance or such for typeof()
   or offsetof() or such
 - instance = mem_to_flex_dup(instance, ...)
   looks too much like it would actually dup 'instance', rather than
   'byte_array'
 - if you pass &instance anyway, checking for NULL is simple and adds a
   bit of safety

but still, honestly, I don't like it. As APIs go, it feels a bit
cumbersome and awkward to use, and you really need everyone to use this,
and not say "uh what, I'll memcpy() instead".

Maybe there should also be a realloc() version of it?


> +/** __fas_bytes - Calculate potential size of flexible array structure

I think you forgot "\n *" in many cases here after "/**".

johannes

  reply	other threads:[~2022-05-04  8:05 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-04  1:44 [PATCH 00/32] Introduce flexible array struct memcpy() helpers Kees Cook
2022-05-04  1:44 ` [PATCH 01/32] netlink: Avoid memcpy() across flexible array boundary Kees Cook
2022-05-04  3:12   ` Introduce flexible array struct memcpy() helpers bluez.test.bot
2022-05-04  3:31   ` [PATCH 01/32] netlink: Avoid memcpy() across flexible array boundary Gustavo A. R. Silva
2022-05-04  3:37     ` Kees Cook
2022-05-04  1:44 ` [PATCH 02/32] Introduce flexible array struct memcpy() helpers Kees Cook
2022-05-04  7:25   ` Johannes Berg [this message]
2022-05-04 15:38     ` Kees Cook
2022-05-04 16:08       ` David Laight
2022-05-05 13:16       ` Johannes Berg
2022-05-05 15:16         ` Keith Packard
2022-05-05 19:32           ` Kees Cook
2022-05-05 20:08             ` Keith Packard
2022-05-05 20:12               ` Johannes Berg
2022-05-06 11:15                 ` David Laight
2022-05-06 11:15                   ` David Laight
2022-05-05 19:27         ` Kees Cook
2022-05-04  1:44 ` [PATCH 03/32] flex_array: Add Kunit tests Kees Cook
2022-05-04  3:00   ` David Gow
2022-05-04 19:43     ` Kees Cook
2022-05-04 19:58   ` Daniel Latypov
2022-05-04  1:44 ` [PATCH 04/32] fortify: Add run-time WARN for cross-field memcpy() Kees Cook
2022-05-04  1:44 ` [PATCH 05/32] brcmfmac: Use mem_to_flex_dup() with struct brcmf_fweh_queue_item Kees Cook
2022-05-16 12:49   ` Arend van Spriel
2022-05-17  3:57     ` Kees Cook
2022-05-04  1:44 ` [PATCH 06/32] iwlwifi: calib: Prepare to use mem_to_flex_dup() Kees Cook
2022-05-04  1:44 ` [PATCH 07/32] iwlwifi: calib: Use mem_to_flex_dup() with struct iwl_calib_result Kees Cook
2022-05-04  1:44 ` [PATCH 08/32] iwlwifi: mvm: Use mem_to_flex_dup() with struct ieee80211_key_conf Kees Cook
2022-05-04  1:44 ` [PATCH 09/32] p54: Use mem_to_flex_dup() with struct p54_cal_database Kees Cook
2022-05-04  1:44 ` [PATCH 10/32] wcn36xx: Use mem_to_flex_dup() with struct wcn36xx_hal_ind_msg Kees Cook
2022-05-04  5:42   ` Kalle Valo
2022-05-04 15:08     ` Kees Cook
2022-05-04  1:44 ` [PATCH 11/32] nl80211: Use mem_to_flex_dup() with struct cfg80211_cqm_config Kees Cook
2022-05-04  1:44 ` [PATCH 12/32] cfg80211: Use mem_to_flex_dup() with struct cfg80211_bss_ies Kees Cook
2022-05-04  7:28   ` Johannes Berg
2022-05-04 15:13     ` Kees Cook
2022-05-04  1:44 ` [PATCH 13/32] mac80211: Use mem_to_flex_dup() with several structs Kees Cook
2022-05-04  1:44 ` [PATCH 14/32] af_unix: Use mem_to_flex_dup() with struct unix_address Kees Cook
2022-05-04  1:44 ` [PATCH 15/32] 802/garp: Use mem_to_flex_dup() with struct garp_attr Kees Cook
2022-05-04  1:44 ` [PATCH 16/32] 802/mrp: Use mem_to_flex_dup() with struct mrp_attr Kees Cook
2022-05-04  1:44 ` [PATCH 17/32] net/flow_offload: Use mem_to_flex_dup() with struct flow_action_cookie Kees Cook
2022-05-04  1:44 ` [PATCH 18/32] firewire: Use __mem_to_flex_dup() with struct iso_interrupt_event Kees Cook
2022-05-04  1:44 ` [PATCH 19/32] afs: Use mem_to_flex_dup() with struct afs_acl Kees Cook
2022-05-04  1:44 ` [PATCH 20/32] ASoC: sigmadsp: Use mem_to_flex_dup() with struct sigmadsp_data Kees Cook
2022-05-04 15:17   ` Mark Brown
2022-05-04  1:44 ` [PATCH 21/32] soc: qcom: apr: Use mem_to_flex_dup() with struct apr_rx_buf Kees Cook
2022-05-04  1:44 ` [PATCH 22/32] atags_proc: Use mem_to_flex_dup() with struct buffer Kees Cook
2022-05-04  1:44 ` [PATCH 23/32] Bluetooth: Use mem_to_flex_dup() with struct hci_op_configure_data_path Kees Cook
2022-05-04  1:44 ` [PATCH 24/32] IB/hfi1: Use mem_to_flex_dup() for struct tid_rb_node Kees Cook
2022-05-04  1:44 ` [PATCH 25/32] Drivers: hv: utils: Use mem_to_flex_dup() with struct cn_msg Kees Cook
2022-05-04  1:44 ` [PATCH 26/32] ima: Use mem_to_flex_dup() with struct modsig Kees Cook
2022-05-04  1:44 ` [PATCH 27/32] KEYS: Use mem_to_flex_dup() with struct user_key_payload Kees Cook
2022-05-04  1:44 ` [PATCH 28/32] selinux: Use mem_to_flex_dup() with xfrm and sidtab Kees Cook
2022-05-04 22:57   ` Paul Moore
2022-05-04 23:43     ` Gustavo A. R. Silva
2022-05-05  3:14       ` Paul Moore
2022-05-05 18:39         ` Kees Cook
2022-05-05 23:16           ` Paul Moore
2022-05-06  1:08             ` Gustavo A. R. Silva
2022-05-04  1:44 ` [PATCH 29/32] xtensa: Use mem_to_flex_dup() with struct property Kees Cook
2022-05-04 18:09   ` Rob Herring
2022-05-04 18:09     ` Rob Herring
2022-05-04  1:44 ` [PATCH 30/32] usb: gadget: f_fs: Use mem_to_flex_dup() with struct ffs_buffer Kees Cook
2022-05-04  1:44 ` [PATCH 31/32] xenbus: Use mem_to_flex_dup() with struct read_buffer Kees Cook
2022-05-04  1:44 ` [PATCH 32/32] esas2r: Use __mem_to_flex() with struct atto_ioctl Kees Cook
2022-05-12 21:41 ` [PATCH 19/32] afs: Use mem_to_flex_dup() with struct afs_acl David Howells
2022-05-12 21:41   ` David Howells
2022-05-13 15:44   ` Kees Cook
2022-05-13 15:44     ` Kees Cook
2022-05-12 21:47 ` [PATCH 00/32] Introduce flexible array struct memcpy() helpers David Howells
2022-05-12 21:47   ` David Howells

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