linux-hardening - RE: [PATCH] kobject: Replace strlcpy with strscpy

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Date:   Mon, 10 Jul 2023 13:13:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Azeem Shaikh' <azeemshaikh38@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] kobject: Replace strlcpy with strscpy

From: Azeem Shaikh
> Sent: 03 July 2023 19:05
> 
> 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>
> ---
>  lib/kobject_uevent.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index 7c44b7ae4c5c..e5497fa0a2d2 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -254,8 +254,8 @@ static int init_uevent_argv(struct kobj_uevent_env *env, const char *subsystem)
>  	int buffer_size = sizeof(env->buf) - env->buflen;
>  	int len;
> 
> -	len = strlcpy(&env->buf[env->buflen], subsystem, buffer_size);
> -	if (len >= buffer_size) {
> +	len = strscpy(&env->buf[env->buflen], subsystem, buffer_size);
> +	if (len < 0) {
>  		pr_warn("init_uevent_argv: buffer size of %d too small, needed %d\n",
>  			buffer_size, len);
>  		return -ENOMEM;

The size in the error message is now wrong.
It has to be said that mostly all the strings that get copied
in the kernel are '\0' terminated - so maybe it is all moot.
OTOH printing (at least some of) the string that didn't fit
is a lot more useful than its length.

	David

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