linux-hardening - Re: [PATCH] tracing/boot: Replace strlcpy with strscpy

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Date:   Tue, 13 Jun 2023 12:27:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/boot: Replace strlcpy with strscpy

On Tue, Jun 13, 2023 at 12:41:25AM +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 -E2BIG
> is used to check for truncation instead of sizeof(dest).

This looks technically correct, but I wonder if "< 0" is a better test?

> 
> [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>

Either way

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

-Kees

> ---
>  kernel/trace/trace_boot.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
> index 778200dd8ede..5fe525f1b8cc 100644
> --- a/kernel/trace/trace_boot.c
> +++ b/kernel/trace/trace_boot.c
> @@ -31,7 +31,7 @@ trace_boot_set_instance_options(struct trace_array *tr, struct xbc_node *node)
>  
>  	/* Common ftrace options */
>  	xbc_node_for_each_array_value(node, "options", anode, p) {
> -		if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf)) {
> +		if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG) {
>  			pr_err("String is too long: %s\n", p);
>  			continue;
>  		}
> @@ -87,7 +87,7 @@ trace_boot_enable_events(struct trace_array *tr, struct xbc_node *node)
>  	const char *p;
>  
>  	xbc_node_for_each_array_value(node, "events", anode, p) {
> -		if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf)) {
> +		if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG) {
>  			pr_err("String is too long: %s\n", p);
>  			continue;
>  		}
> @@ -486,7 +486,7 @@ trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
>  
>  	p = xbc_node_find_value(enode, "filter", NULL);
>  	if (p && *p != '\0') {
> -		if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf))
> +		if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG)
>  			pr_err("filter string is too long: %s\n", p);
>  		else if (apply_event_filter(file, buf) < 0)
>  			pr_err("Failed to apply filter: %s\n", buf);
> @@ -494,7 +494,7 @@ trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
>  
>  	if (IS_ENABLED(CONFIG_HIST_TRIGGERS)) {
>  		xbc_node_for_each_array_value(enode, "actions", anode, p) {
> -			if (strlcpy(buf, p, ARRAY_SIZE(buf)) >= ARRAY_SIZE(buf))
> +			if (strscpy(buf, p, ARRAY_SIZE(buf)) == -E2BIG)
>  				pr_err("action string is too long: %s\n", p);
>  			else if (trigger_process_regex(file, buf) < 0)
>  				pr_err("Failed to apply an action: %s\n", p);
> -- 
> 2.41.0.162.gfafddb0af9-goog
> 
> 

-- 
Kees Cook