[PATCH v2] net: wwan: replace deprecated strncpy with strscpy

[Justin Stitt <justinstitt@google.com>]

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

We expect chinfo.name to be NUL-terminated based on its use with format
strings and sprintf:
rpmsg/rpmsg_char.c
165:            dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
368:    return sprintf(buf, "%s\n", eptdev->chinfo.name);

... and with strcmp():
|  static struct rpmsg_endpoint *qcom_glink_create_ept(struct rpmsg_device *rpdev,
|  						    rpmsg_rx_cb_t cb,
|  						    void *priv,
|  						    struct rpmsg_channel_info
|  									chinfo)
|  ...
|  const char *name = chinfo.name;
|  ...
|  		if (!strcmp(channel->name, name))

Since chinfo is initialized as such (just above the strscpy()):

|       struct rpmsg_channel_info chinfo = {
|               .src = rpwwan->rpdev->src,
|               .dst = RPMSG_ADDR_ANY,
|       };

... we know other members are zero-initialized. This means no
NUL-padding is required (as any NUL-byte assignments are redundant).

Considering the above, a suitable replacement is `strscpy` 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://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
Changes in v2:
- clarify chinfo _is_ zero-init'd in commit msg (thanks Stephan)
- use strscpy instead (thanks Kees, Stephan)
- Link to v1: https://lore.kernel.org/r/20231018-strncpy-drivers-net-wwan-rpmsg_wwan_ctrl-c-v1-1-4e343270373a@google.com
---
Note: found with grep
Note: build-tested only

I've rolled Kees' RB into this patch from v1 as it matches his previous
review.
---
 drivers/net/wwan/rpmsg_wwan_ctrl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wwan/rpmsg_wwan_ctrl.c b/drivers/net/wwan/rpmsg_wwan_ctrl.c
index 86b60aadfa11..26756ff0e44d 100644
--- a/drivers/net/wwan/rpmsg_wwan_ctrl.c
+++ b/drivers/net/wwan/rpmsg_wwan_ctrl.c
@@ -37,7 +37,7 @@ static int rpmsg_wwan_ctrl_start(struct wwan_port *port)
 		.dst = RPMSG_ADDR_ANY,
 	};
 
-	strncpy(chinfo.name, rpwwan->rpdev->id.name, RPMSG_NAME_SIZE);
+	strscpy(chinfo.name, rpwwan->rpdev->id.name, sizeof(chinfo.name));
 	rpwwan->ept = rpmsg_create_ept(rpwwan->rpdev, rpmsg_wwan_ctrl_callback,
 				       rpwwan, chinfo);
 	if (!rpwwan->ept)

---
base-commit: 58720809f52779dc0f08e53e54b014209d13eebb
change-id: 20231018-strncpy-drivers-net-wwan-rpmsg_wwan_ctrl-c-3f620aafd326

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