linux-hardening - [PATCH] net: txgbe: replace deprecated strncpy with strscpy

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Date: Thu, 12 Oct 2023 21:20:04 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Jiawen Wu <jiawenwu@...stnetic.com>, Mengyuan Lou <mengyuanlou@...-swift.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] net: txgbe: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

Based on usage part_str usage within txgbe_read_pba_string(), we expect
part_str to be NUL-terminated but not necessarily NUL-padded:
|       /* put a null character on the end of our string */
|       pba_num[10] = '\0';

Interestingly, part_str is not used after txgbe_read_pba_string():
| ...
|	err = txgbe_read_pba_string(wx, part_str, TXGBE_PBANUM_LENGTH);
|	if (err)
|		strscpy(part_str, "Unknown", sizeof(part_str));
|
|	netif_info(wx, probe, netdev, "%pM\n", netdev->dev_addr);
|
|	return 0;
|
|err_remove_phy:
|	txgbe_remove_phy(txgbe);
|err_release_hw:
|	wx_clear_interrupt_scheme(wx);
|	wx_control_hw(wx, false);
|err_free_mac_table:
|	kfree(wx->mac_table);
|err_pci_release_regions:
|	pci_release_selected_regions(pdev,
|				     pci_select_bars(pdev, IORESOURCE_MEM));
|err_pci_disable_dev:
|	pci_disable_device(pdev);
|	return err;
|}
... this means this strncpy (or now strscpy) is probably useless. For
now, let's make the swap to strscpy() as I am not sure if this is truly
dead code or not.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
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/ethernet/wangxun/txgbe/txgbe_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/wangxun/txgbe/txgbe_main.c b/drivers/net/ethernet/wangxun/txgbe/txgbe_main.c
index 5c3aed516ac2..c795fbab37be 100644
--- a/drivers/net/ethernet/wangxun/txgbe/txgbe_main.c
+++ b/drivers/net/ethernet/wangxun/txgbe/txgbe_main.c
@@ -739,7 +739,7 @@ static int txgbe_probe(struct pci_dev *pdev,
 	/* First try to read PBA as a string */
 	err = txgbe_read_pba_string(wx, part_str, TXGBE_PBANUM_LENGTH);
 	if (err)
-		strncpy(part_str, "Unknown", TXGBE_PBANUM_LENGTH);
+		strscpy(part_str, "Unknown", sizeof(part_str));

 	netif_info(wx, probe, netdev, "%pM\n", netdev->dev_addr);

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231012-strncpy-drivers-net-ethernet-wangxun-txgbe-txgbe_main-c-05152bafac20

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