linux-kernel - Re: [PATCH] ath10k: replace deprecated strncpy with strtomem

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Message-ID: <1cfc7c64-439c-437e-af82-7fce1202242d@quicinc.com>
Date:   Fri, 13 Oct 2023 17:58:03 -0700
From:   Jeff Johnson <quic_jjohnson@...cinc.com>
To:     Justin Stitt <justinstitt@...gle.com>,
        Kalle Valo <kvalo@...nel.org>
CC:     <ath10k@...ts.infradead.org>, <linux-wireless@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH] ath10k: replace deprecated strncpy with strtomem_pad

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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

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