Re: [PATCH] net: wwan: replace deprecated strncpy with strscpy_pad

Kees Cook
2023-10-19T05:35:43Z

On Wed, Oct 18, 2023 at 10:14:55PM +0000, Justin Stitt wrote:
> 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))
>
> Moreover, as chinfo is not kzalloc'd, let's opt to NUL-pad the
> destination buffer
>
> Similar change to:
> Commit 766279a8f85d ("rpmsg: qcom: glink: replace strncpy() with strscpy_pad()")
> and
> Commit 08de420a8014 ("rpmsg: glink: Replace strncpy() with strscpy_pad()")
>
> Considering the above, a suitable replacement is `strscpy_pad` due to
> the fact that it guarantees both NUL-termination and NUL-padding on the
> destination buffer.
>
> 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>
> ---
> Note: build-tested only.
>
> Found with: $ rg "strncpy\("
> ---
> 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..39f5e780c478 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,
> };

"chinfo" is initialized immediately above here, which means that it is
actually already zero filled for all the members that aren't explicitly
initialized, so the _pad variant isn't needed. I suspect Dead Store
Elimination will optimize it all away anyway, so this is probably fine.

>
> - strncpy(chinfo.name, rpwwan->rpdev->id.name, RPMSG_NAME_SIZE);
> + strscpy_pad(chinfo.name, rpwwan->rpdev->id.name, sizeof(chinfo.name));

Yup, sizeof() replacement looks correct:

struct rpmsg_channel_info {
char name[RPMSG_NAME_SIZE];

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

--
Kees Cook