linux-hardening - Re: [PATCH] init/version.c: Replace strlcpy with strscpy

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Date:   Wed, 30 Aug 2023 14:17:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Thomas Weißschuh <linux@...ssschuh.net>
Subject: Re: [PATCH] init/version.c: Replace strlcpy with strscpy

On Wed, Aug 30, 2023 at 04:08:06PM +0000, Azeem Shaikh wrote:
> strlcpy() reads the entire source buffer first.
> This read may exceed the destination size limit.
> This is both inefficient and can lead to linear read
> overflows if a source string is not NUL-terminated [1].
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with strscpy().
> 
> Direct replacement is safe here since return value of -errno
> is used to check for truncation instead of sizeof(dest).
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
> 
> Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
> ---
>  init/version.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/init/version.c b/init/version.c
> index f117921811b4..94c96f6fbfe6 100644
> --- a/init/version.c
> +++ b/init/version.c
> @@ -21,10 +21,10 @@ static int __init early_hostname(char *arg)
>  {
>  	size_t bufsize = sizeof(init_uts_ns.name.nodename);
>  	size_t maxlen  = bufsize - 1;
> -	size_t arglen;
> +	ssize_t arglen;
> 
> -	arglen = strlcpy(init_uts_ns.name.nodename, arg, bufsize);
> -	if (arglen > maxlen) {
> +	arglen = strscpy(init_uts_ns.name.nodename, arg, bufsize);
> +	if (arglen < 0) {

nitpick: this is no longer "length of arg", it's the length of the
destination string. Regardless:

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

>  		pr_warn("hostname parameter exceeds %zd characters and will be truncated",
>  			maxlen);
>  	}
> --
> 2.41.0.255.g8b1d071c50-goog
> 
> 

-- 
Kees Cook