linux-hardening - Re: [PATCH v2] wifi: ath10k: replace deprecated strncpy with memcpy

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Date: Tue, 24 Oct 2023 14:34:01 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Kalle Valo <kvalo@...nel.org>, Jeff Johnson <quic_jjohnson@...cinc.com>,
	ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] wifi: ath10k: replace deprecated strncpy with memcpy

On Tue, Oct 24, 2023 at 05:42:16PM +0000, Justin Stitt wrote:
> strncpy() is deprecated [1] and we should prefer less ambiguous
> interfaces.
> 
> In this case, arvif->u.ap.ssid has its length maintained by
> arvif->u.ap.ssid_len which indicates it may not need to be
> NUL-terminated. Make this explicit with __nonstring and use a plain old
> memcpy.
> 
> This is also consistent with future copies into arvif->u.ap.ssid:
> 
> 	if (changed & BSS_CHANGED_SSID &&
> 	    vif->type == NL80211_IFTYPE_AP) {
> 		arvif->u.ap.ssid_len = vif->cfg.ssid_len;
> 		if (vif->cfg.ssid_len)
> 			memcpy(arvif->u.ap.ssid, vif->cfg.ssid,
> 			       vif->cfg.ssid_len);
> 		arvif->u.ap.hidden_ssid = info->hidden_ssid;
> 	}
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Changes in v2:
> - update subject to include wifi
> - prefer memcpy() over strtomem() (thanks Kalle, Jeff)
> - rebase onto 6.6-rc7 @d88520ad73b79e71
> - Link to v1: https://lore.kernel.org/r/20231013-strncpy-drivers-net-wireless-ath-ath10k-mac-c-v1-1-24e40201afa3@google.com
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/net/wireless/ath/ath10k/core.h | 2 +-
>  drivers/net/wireless/ath/ath10k/mac.c  | 3 +--
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath10k/core.h b/drivers/net/wireless/ath/ath10k/core.h
> index 4b5239de4018..ba9795a8378a 100644
> --- a/drivers/net/wireless/ath/ath10k/core.h
> +++ b/drivers/net/wireless/ath/ath10k/core.h
> @@ -607,7 +607,7 @@ struct ath10k_vif {
>  			u8 tim_bitmap[64];
>  			u8 tim_len;
>  			u32 ssid_len;
> -			u8 ssid[IEEE80211_MAX_SSID_LEN];
> +			u8 ssid[IEEE80211_MAX_SSID_LEN] __nonstring;
>  			bool hidden_ssid;
>  			/* P2P_IE with NoA attribute for P2P_GO case */
>  			u32 noa_len;
> diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
> index 03e7bc5b6c0b..f3f6deb354c6 100644
> --- a/drivers/net/wireless/ath/ath10k/mac.c
> +++ b/drivers/net/wireless/ath/ath10k/mac.c
> @@ -6125,9 +6125,8 @@ static void ath10k_bss_info_changed(struct ieee80211_hw *hw,
>  
>  		if (ieee80211_vif_is_mesh(vif)) {
>  			/* mesh doesn't use SSID but firmware needs it */
> -			strncpy(arvif->u.ap.ssid, "mesh",
> -				sizeof(arvif->u.ap.ssid));
>  			arvif->u.ap.ssid_len = 4;
> +			memcpy(arvif->u.ap.ssid, "mesh", arvif->u.ap.ssid_len);

This is a behavior change, isn't it? i.e. arvif->u.ap.ssid is no longer
zero-padded. Is this actually ok for the driver?

-Kees

-- 
Kees Cook