linux-kernel - [PATCH] ath10k: replace deprecated strncpy with strtomem

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Message-ID: <20231013-strncpy-drivers-net-wireless-ath-ath10k-mac-c-v1-1-24e40201afa3@google.com>
Date:   Fri, 13 Oct 2023 20:33:48 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Kalle Valo <kvalo@...nel.org>,
        Jeff Johnson <quic_jjohnson@...cinc.com>
Cc:     ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] ath10k: replace deprecated strncpy with strtomem_pad

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, although by virtue of using strtomem_pad (with NUL-byte
pad character) and having a destination size larger than the source,
ssid will, incidentally, be NUL-terminated here.

As strtomem_pad() docs say:
 * @dest: Pointer of destination character array (marked as __nonstring)
 * @src: Pointer to NUL-terminated string
 * @pad: Padding character to fill any remaining bytes of @dest after copy
 *
 * This is a replacement for strncpy() uses where the destination is not
 * a NUL-terminated string, but with bounds checking on the source size, and
 * an explicit padding character. If padding is not required, use strtomem().

Let's also mark ath10k_vif.u.ap.ssid as __nonstring.

It is unclear to me whether padding is strictly necessary. Perhaps we
should opt for just strtomem() -- padding certainly doesn't hurt,
though.

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>
---
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..7daa007bd8b3 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c
@@ -6125,8 +6125,7 @@ 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));
+			strtomem_pad(arvif->u.ap.ssid, "mesh", '\0');
 			arvif->u.ap.ssid_len = 4;
 		}
 	}

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231013-strncpy-drivers-net-wireless-ath-ath10k-mac-c-c73a55666e6a

Best regards,
--
Justin Stitt <justinstitt@...gle.com>