Re: [PATCH 27/28] drm/xe/pf: Convert strlcat() to seq_buf in control_read()

[Kees Cook]

On Tue, Sep 15, 2026 at 08:18:44AM +0000, Bill Wendling wrote:
> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c b/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c
> index 0f242db775e1..5db7fc067c4d 100644
> --- a/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c
> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_pf_debugfs.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include <linux/debugfs.h>
> +#include <linux/seq_buf.h>
>  
>  #include <drm/drm_print.h>
>  #include <drm/drm_debugfs.h>
> @@ -663,15 +664,15 @@ static ssize_t control_write(struct file *file, const char __user *buf, size_t c
>  static ssize_t control_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  {
>  	char help[128];
> +	struct seq_buf s;
>  	size_t n;
>  
> -	help[0] = '\0';
> +	seq_buf_init(&s, help, sizeof(help));
>  	for (n = 0; n < ARRAY_SIZE(control_cmds); n++) {
> -		strlcat(help, control_cmds[n].cmd, sizeof(help));
> -		strlcat(help, "\n", sizeof(help));
> +		seq_buf_printf(&s, "%s\n", control_cmds[n].cmd);
>  	}

Yay seq_buf! I would tweak the 3 init stack variable lines into just
using the single DECLARE_SEQ_BUF:

DECLARE_SEQ_BUF(s, 128);

>  
> -	return simple_read_from_buffer(buf, count, ppos, help, strlen(help));
> +	return simple_read_from_buffer(buf, count, ppos, help, seq_buf_used(&s));

seq_buf_used() isn't correct in the case of full-buffer use. e.g. if
the help buffer ends up filled with 127 chars and a NUL terminator,
seq_buf_used() returns 128, but you want 127 here. Using strlen() ends up
being redundant, though. I think we need to add seq_buf_strlen() which
handles the same logic that seq_buf_str() does.

-Kees

-- 
Kees Cook