Re: [PATCH] ath10k: replace deprecated strncpy with strtomem_pad

[Jeff Johnson]

On 10/13/2023 1:33 PM, Justin Stitt wrote:
> 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.

what criteria is used to determine whether or not to use __nonstring?
doesn't the use of u8 vs char already communicate that distinction?
just want to know what other u8 arrays might require this.
FWIW the documentation referenced by the __nonstring macro explicitly 
refers to "type array of char, signed char, or unsigned char"

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

concur that padding probably isn't necessary but doesn't hurt, and will 
prevent confusion if looking at this member in a crashdump

> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>

Either with or without the __nonstring...
Acked-by: Jeff Johnson <quic_jjohnson@xxxxxxxxxxx>