linux-kernel - [PATCH v2 2/2] wifi: mwifiex: Annotate mwifiex_ie_types_wildcard_ssid_params with __counted

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Message-ID: <20241007222301.24154-2-alpernebiyasak@gmail.com>
Date: Tue,  8 Oct 2024 01:20:55 +0300
From: Alper Nebi Yasak <alpernebiyasak@...il.com>
To: linux-wireless@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Francesco Dolcini <francesco@...cini.it>,
	Johannes Berg <johannes.berg@...el.com>,
	Kees Cook <kees@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Dmitry Antipov <dmantipov@...dex.ru>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Brian Norris <briannorris@...omium.org>,
	David Lin <yu-hao.lin@....com>,
	linux-hardening@...r.kernel.org,
	Kalle Valo <kvalo@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Alper Nebi Yasak <alpernebiyasak@...il.com>
Subject: [PATCH v2 2/2] wifi: mwifiex: Annotate mwifiex_ie_types_wildcard_ssid_params with __counted_by()

Add the __counted_by compiler attribute to the flexible array member
`ssid` to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@...il.com>
---
I've mimicked the commit messages from `git log -S"__counted_by("`.
Since they refer to UBSAN I tried testing with CONFIG_KASAN (w/
kasan_multi_shot), CONFIG_UBSAN and CONFIG_FORTIFY_SOURCE. I do not
get any errors relating to this module with those options, but have
others -- I even had to test on another board altogether.

This attribute was suggested in reviews, I don't fully understand it,
but I am not sure it is correct in the context of this comment from
scan.c (with irrelelvant parts omitted):

    ssid_len = user_scan_in->ssid_list[i].ssid_len;

    wildcard_ssid_tlv =
            (struct mwifiex_ie_types_wildcard_ssid_params *)
            tlv_pos;

    /*
     * max_ssid_length = 0 tells firmware to perform
     * specific scan for the SSID filled, whereas
     * max_ssid_length = IEEE80211_MAX_SSID_LEN is for
     * wildcard scan.
     */
    if (ssid_len)
            wildcard_ssid_tlv->max_ssid_length = 0;
    else
            wildcard_ssid_tlv->max_ssid_length =
                                    IEEE80211_MAX_SSID_LEN;

    memcpy(wildcard_ssid_tlv->ssid,
           user_scan_in->ssid_list[i].ssid, ssid_len);

I expect we want to use __counted_by(ssid_len) instead, but do not have
it in the struct. And max_ssid_length = 0 when ssid[] is non-empty, so
is it really appropriate as the __counted_by()? But then again, I
couldn't get this to produce a warning.

Changes in v2:
- Add patch to annotate ssid field with __counted_by(max_ssid_length)

 drivers/net/wireless/marvell/mwifiex/fw.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/fw.h b/drivers/net/wireless/marvell/mwifiex/fw.h
index 4a96281792cc..e4e35ba35454 100644
--- a/drivers/net/wireless/marvell/mwifiex/fw.h
+++ b/drivers/net/wireless/marvell/mwifiex/fw.h
@@ -875,7 +875,7 @@ struct mwifiex_ietypes_chanstats {
 struct mwifiex_ie_types_wildcard_ssid_params {
 	struct mwifiex_ie_types_header header;
 	u8 max_ssid_length;
-	u8 ssid[];
+	u8 ssid[] __counted_by(max_ssid_length);
 } __packed;
 
 #define TSF_DATA_SIZE            8
-- 
2.45.2