Re: [PATCH] net: tun: fix strscpy call with missing size argument

[Willem de Bruijn]

On Thu, Aug 14, 2025 at 7:23 PM Zhang Tengfei <zhtfdev@xxxxxxxxx> wrote:
>
> The tun_set_iff() and tun_get_iff() functions call strscpy()
> with only two arguments, omitting the destination buffer size.
>
> This patch corrects these calls by providing the required size
> argument using the IFNAMSIZ macro. This ensures the code adheres
> to the function's documented contract and improves its overall
> robustness and clarity.
>
> Fixes: a57384110dc6 ("tun: replace strcpy with strscpy for ifr_name")
> Signed-off-by: Zhang Tengfei <zhtfdev@xxxxxxxxx>

The two argument choice is intentional. In that case the length is
taken from the struct field sizes, which is more robust than an
explicit argument.

https://lore.kernel.org/netdev/6899fde3dbfd6_532b129461@xxxxxxxxxxxxxxxxxxxxxx.notmuch/


> ---
>  drivers/net/tun.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 86a9e927d0ff..88c440c99542 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2823,13 +2823,13 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>         if (netif_running(tun->dev))
>                 netif_tx_wake_all_queues(tun->dev);
>
> -       strscpy(ifr->ifr_name, tun->dev->name);
> +       strscpy(ifr->ifr_name, tun->dev->name, IFNAMSIZ);
>         return 0;
>  }
>
>  static void tun_get_iff(struct tun_struct *tun, struct ifreq *ifr)
>  {
> -       strscpy(ifr->ifr_name, tun->dev->name);
> +       strscpy(ifr->ifr_name, tun->dev->name, IFNAMSIZ);
>
>         ifr->ifr_flags = tun_flags(tun);
>
> --
> 2.47.3
>