linux-kernel - Re: [PATCH] wifi: brcmfmac: Replace 1-element arrays with flexible arrays

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Message-ID: <0f23e4a2-b11b-98bd-c419-d9a9fb7ddb4e@embeddedor.com>
Date:   Wed, 13 Sep 2023 10:02:12 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Juerg Haefliger <juerg.haefliger@...onical.com>, aspriel@...il.com,
        franky.lin@...adcom.com, hante.meuleman@...adcom.com,
        kvalo@...nel.org, linux-wireless@...r.kernel.org,
        brcm80211-dev-list.pdl@...adcom.com,
        SHA-cyfmac-dev-list@...ineon.com
Cc:     linux-kernel@...r.kernel.org, linus.walleij@...aro.org,
        marcan@...can.st, keescook@...omium.org, gustavoars@...nel.org,
        hdegoede@...hat.com, ryohei.kondo@...ress.com
Subject: Re: [PATCH] wifi: brcmfmac: Replace 1-element arrays with flexible
 arrays



On 9/13/23 00:54, Juerg Haefliger wrote:
> Since commit 2d47c6956ab3 ("ubsan: Tighten UBSAN_BOUNDS on GCC"),
> UBSAN_BOUNDS no longer pretends 1-element arrays are unbounded. Walking
> 'element' and 'channel_list' will trigger warnings, so make them proper
> flexible arrays.
> 
> False positive warnings were:
> 
>    UBSAN: array-index-out-of-bounds in drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:6984:20
>    index 1 is out of range for type '__le32 [1]'
> 
>    UBSAN: array-index-out-of-bounds in drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:1126:27
>    index 1 is out of range for type '__le16 [1]'
> 
> for these lines of code:
> 
>    6884  ch.chspec = (u16)le32_to_cpu(list->element[i]);
> 
>    1126  params_le->channel_list[i] = cpu_to_le16(chanspec);
> 
> Signed-off-by: Juerg Haefliger <juerg.haefliger@...onical.com>
> ---
>   .../wireless/broadcom/brcm80211/brcmfmac/fwil_types.h    | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h
> index bece26741d3a..ed723a5b5d54 100644
> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h
> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil_types.h
> @@ -442,7 +442,12 @@ struct brcmf_scan_params_v2_le {
>   				 * fixed parameter portion is assumed, otherwise
>   				 * ssid in the fixed portion is ignored
>   				 */
> -	__le16 channel_list[1];	/* list of chanspecs */
> +	union {
> +		__le16 padding;	/* Reserve space for at least 1 entry for abort
> +				 * which uses an on stack brcmf_scan_params_v2_le
> +				 */
> +		DECLARE_FLEX_ARRAY(__le16, channel_list);	/* chanspecs */
> +	};
>   };
>   
>   struct brcmf_scan_results {
> @@ -702,7 +707,7 @@ struct brcmf_sta_info_le {
>   
>   struct brcmf_chanspec_list {
>   	__le32	count;		/* # of entries */
> -	__le32	element[1];	/* variable length uint32 list */
> +	DECLARE_FLEX_ARRAY(__le32, element);	/* variable length uint32 list */

If no padding is needed, as in the other case, then DFA() is not necessary.
Just remove the 1 from the array declaration:

  struct brcmf_chanspec_list {
         __le32  count;          /* # of entries */
-       __le32  element[1];     /* variable length uint32 list */
+       __le32  element[];      /* variable length uint32 list */
  };

--
Gustavo

>   };
>   
>   /*