linux-hardening - Re: [PATCH v2][next] wifi: wil6210: Annotate a couple of structs with __counted

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Date: Wed, 27 Mar 2024 11:26:22 -0700
From: Jeff Johnson <quic_jjohnson@...cinc.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kalle Valo
	<kvalo@...nel.org>
CC: <linux-wireless@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v2][next] wifi: wil6210: Annotate a couple of structs with
 __counted_by()

On 3/27/2024 10:43 AM, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> Changes in v2:
>  - Annotate one more struct.
>  - Update Subject line.
> 
> v1:
>  - Link: https://lore.kernel.org/linux-hardening/ZgODZOB4fOBvKl7R@neat/
> 
>  drivers/net/wireless/ath/wil6210/wmi.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/wil6210/wmi.h b/drivers/net/wireless/ath/wil6210/wmi.h
> index 71bf2ae27a98..38f64524019e 100644
> --- a/drivers/net/wireless/ath/wil6210/wmi.h
> +++ b/drivers/net/wireless/ath/wil6210/wmi.h
> @@ -474,7 +474,7 @@ struct wmi_start_scan_cmd {
>  	struct {
>  		u8 channel;
>  		u8 reserved;
> -	} channel_list[];
> +	} channel_list[] __counted_by(num_channels);
>  } __packed;

does the compiler handle the actual logic where it is modifying num_channels
concurrently with writing into the array? i.e. this will be writing into
channel_list[0] when num_channels is 0:

		cmd.cmd.channel_list[cmd.cmd.num_channels++].channel = ch - 1;

if that will cause a bounds check failure then suggest you change the logic so
that it updates num_channels before writing into channel_list

>  
>  #define WMI_MAX_PNO_SSID_NUM	(16)
> @@ -3320,7 +3320,7 @@ struct wmi_set_link_monitor_cmd {
>  	u8 rssi_hyst;
>  	u8 reserved[12];
>  	u8 rssi_thresholds_list_size;
> -	s8 rssi_thresholds_list[];
> +	s8 rssi_thresholds_list[] __counted_by(rssi_thresholds_list_size);
>  } __packed;

this looks ok to me, although I think there is another issue associated with
this, namely the way the code populates the rssi_thresholds_list is by
defining a separate anonymous struct:
	struct {
		struct wmi_set_link_monitor_cmd cmd;
		s8 rssi_thold;
	} __packed cmd = {
		.cmd = {
			.rssi_hyst = rssi_hyst,
			.rssi_thresholds_list_size = 1,
		},
		.rssi_thold = rssi_thold,
	};

I would expect gcc and clang to both complain about that s8 rssi_thold comes
after a flexible array (even though its purpose is to be the value of
rssi_thresholds_list[0])

/jeff


>  
>  /* wmi_link_monitor_event_type */