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From: Kees Cook <keescook@chromium.org>
To: Kalle Valo <kvalo@kernel.org>
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Subject: Re: [PATCH 10/32] wcn36xx: Use mem_to_flex_dup() with struct wcn36xx_hal_ind_msg
Date: Wed, 4 May 2022 08:08:26 -0700	[thread overview]
Message-ID: <202205040730.161645EC@keescook> (raw)
In-Reply-To: <8735hpc0q1.fsf@kernel.org>

On Wed, May 04, 2022 at 08:42:46AM +0300, Kalle Valo wrote:
> Kees Cook <keescook@chromium.org> writes:
> 
> > As part of the work to perform bounds checking on all memcpy() uses,
> > replace the open-coded a deserialization of bytes out of memory into a
> > trailing flexible array by using a flex_array.h helper to perform the
> > allocation, bounds checking, and copying.
> >
> > Cc: Loic Poulain <loic.poulain@linaro.org>
> > Cc: Kalle Valo <kvalo@kernel.org>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > Cc: Eric Dumazet <edumazet@google.com>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Paolo Abeni <pabeni@redhat.com>
> > Cc: wcn36xx@lists.infradead.org
> > Cc: linux-wireless@vger.kernel.org
> > Cc: netdev@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> [...]
> 
> > --- a/drivers/net/wireless/ath/wcn36xx/smd.h
> > +++ b/drivers/net/wireless/ath/wcn36xx/smd.h
> > @@ -46,8 +46,8 @@ struct wcn36xx_fw_msg_status_rsp {
> >  
> >  struct wcn36xx_hal_ind_msg {
> >  	struct list_head list;
> > -	size_t msg_len;
> > -	u8 msg[];
> > +	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(size_t, msg_len);
> > +	DECLARE_FLEX_ARRAY_ELEMENTS(u8, msg);
> 
> This affects readability quite a lot and tbh I don't like it. Isn't
> there any simpler way to solve this?

Similar to how I plumbed member names into __mem_to_flex(), I could do
the same for __mem_to_flex_dup(). That way if the struct member aliases
(DECLARE_FLEX...)  aren't added, the longer form of the helper could
be used. Instead of:

	if (mem_to_flex_dup(&msg_ind, buf, len, GFP_ATOMIC)) {

it would be:

	if (__mem_to_flex_dup(&msg_ind, /* self */, msg,
			      msg_len, buf, len, GFP_ATOMIC)) {

This was how I'd written the helpers in an earlier version, but it
seemed much cleaner to avoid repeating structure layout details at each
call site.

I couldn't find any other way to encode the needed information. It'd be
wonderful if C would let us do:

	struct wcn36xx_hal_ind_msg {
		struct list_head list;
		size_t msg_len;
		u8 msg[msg_len];
	}

And provide some kind of interrogation:

	__builtin_flex_array_member(msg_ind) -> msg_ind->msg
	__builtin_flex_array_count(msg_ind)  -> msg_ind->msg_len

My hope would be to actually use the member aliases to teach things like
-fsanitize=array-bounds about flexible arrays. If it encounters a
structure with the aliases, it could add the instrumentation to do the
bounds checking of things like:

	msg_ind->msg[42]; /* check that 42 is < msg_ind->msg_len */

I also wish I could find a way to make the proposed macros "forward
portable" into proposed C syntax above, but this eluded me as well.
For example:

	struct wcn36xx_hal_ind_msg {
		size_t msg_len;
		struct list_head list;
		BOUNDED_FLEX_ARRAY(u8, msg, msg_len);
	}

	#ifdef CC_HAS_DYNAMIC_ARRAY_LEN
	# define BOUNDED_FLEX_ARRAY(type, name, bounds)	type name[bounds]
	#else
	# define BOUNDED_FLEX_ARRAY(type, name, bounds)			\
		magic_alias_of msg_len __flex_array_elements_count;	\
		union {							\
			type name[];					\
			type __flex_array_elements[];			\
		}
	#endif

But I couldn't sort out the "magic_alias_of" syntax that wouldn't force
structures into having the count member immediately before the flex
array, which would impose more limitations on where this could be
used...

Anyway, I'm open to ideas on how to improve this!

-Kees

-- 
Kees Cook

  reply	other threads:[~2022-05-04 15:08 UTC|newest]

Thread overview: 63+ 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  3:31   ` 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
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
2022-05-05 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
2022-05-04  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 [this message]
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  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
2022-05-13 15:44   ` Kees Cook
2022-05-12 21:47 ` [PATCH 00/32] Introduce flexible array struct memcpy() helpers David Howells

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