Re: [PATCH v2] selinux: replace strlcat() with seq_buf in selinux_ima_collect_state()

[David Laight <david.laight.linux@gmail.com>]

On Fri, 26 Jun 2026 10:57:10 -0500
Ian Bridges <icb@fastmail.org> wrote:

> In preparation for removing the deprecated strlcat() API[1], replace the
> strscpy()/strlcat() chain in selinux_ima_collect_state() with a struct
> seq_buf, which tracks the write position and remaining space internally.
> 
> Each field is written with seq_buf_printf() using a "=%d;" format, which
> removes the open-coded "=1;"/"=0;" constants. The seven per-append
> WARN_ON(rc >= buf_len) truncation checks are replaced by a single
> seq_buf_has_overflowed() check after the string is built.
> 
> Link: https://github.com/KSPP/linux/issues/370 [1]
> Signed-off-by: Ian Bridges <icb@fastmail.org>
> ---
> Changed in v2: replace the v1 seq_buf_puts() pairs with seq_buf_printf()
> using a "=%d;" format, which drops the open-coded "=1;"/"=0;" constants.

Did you verify that all the values are 0/1 otherwise a !! prefix might
be needed.

> 
> v1: https://lore.kernel.org/all/ajlN94VO7BYNUTAy@dev/
> 
> I didn't change the precomputation of the string size. An alternative,
> which is used by other seq_buf callers (e.g. kernel/rcu/refscale.c,
> mm/memcontrol.c), is to drop the precomputation and allocate an oversized
> fixed buffer, relying on the seq_buf overflow check as a backstop. I'm
> happy to rework the patch to adopt that alternative.

That would be reasonable, the output is always exactly the same length and
the buffer is freed just after being allocated.
A comment that there are 3 + 15 strings and all are under 32 bytes so 1k
is plenty would suffice.

	David

> 
>  security/selinux/ima.c | 40 +++++++++++++---------------------------
>  1 file changed, 13 insertions(+), 27 deletions(-)
> 
> diff --git a/security/selinux/ima.c b/security/selinux/ima.c
> index aa34da9b0aeb..cb0efa2fc1ad 100644
> --- a/security/selinux/ima.c
> +++ b/security/selinux/ima.c
> @@ -9,6 +9,7 @@
>   */
>  #include <linux/vmalloc.h>
>  #include <linux/ima.h>
> +#include <linux/seq_buf.h>
>  #include "security.h"
>  #include "ima.h"
>  
> @@ -20,46 +21,31 @@
>   */
>  static char *selinux_ima_collect_state(void)
>  {
> -	const char *on = "=1;", *off = "=0;";
> +	struct seq_buf s;
>  	char *buf;
> -	int buf_len, len, i, rc;
> +	int buf_len, suffix_len, i;
>  
>  	buf_len = strlen("initialized=0;enforcing=0;checkreqprot=0;") + 1;
> +	suffix_len = strlen("=0;");
>  
> -	len = strlen(on);
>  	for (i = 0; i < __POLICYDB_CAP_MAX; i++)
> -		buf_len += strlen(selinux_policycap_names[i]) + len;
> +		buf_len += strlen(selinux_policycap_names[i]) + suffix_len;
>  
>  	buf = kzalloc(buf_len, GFP_KERNEL);
>  	if (!buf)
>  		return NULL;
>  
> -	rc = strscpy(buf, "initialized", buf_len);
> -	WARN_ON(rc < 0);
> +	seq_buf_init(&s, buf, buf_len);
>  
> -	rc = strlcat(buf, selinux_initialized() ? on : off, buf_len);
> -	WARN_ON(rc >= buf_len);
> +	seq_buf_printf(&s, "initialized=%d;enforcing=%d;checkreqprot=%d;",
> +		       selinux_initialized(), enforcing_enabled(),
> +		       checkreqprot_get());
>  
> -	rc = strlcat(buf, "enforcing", buf_len);
> -	WARN_ON(rc >= buf_len);
> -
> -	rc = strlcat(buf, enforcing_enabled() ? on : off, buf_len);
> -	WARN_ON(rc >= buf_len);
> -
> -	rc = strlcat(buf, "checkreqprot", buf_len);
> -	WARN_ON(rc >= buf_len);
> -
> -	rc = strlcat(buf, checkreqprot_get() ? on : off, buf_len);
> -	WARN_ON(rc >= buf_len);
> -
> -	for (i = 0; i < __POLICYDB_CAP_MAX; i++) {
> -		rc = strlcat(buf, selinux_policycap_names[i], buf_len);
> -		WARN_ON(rc >= buf_len);
> +	for (i = 0; i < __POLICYDB_CAP_MAX; i++)
> +		seq_buf_printf(&s, "%s=%d;", selinux_policycap_names[i],
> +			       selinux_state.policycap[i]);
>  
> -		rc = strlcat(buf, selinux_state.policycap[i] ? on : off,
> -			buf_len);
> -		WARN_ON(rc >= buf_len);
> -	}
> +	WARN_ON(seq_buf_has_overflowed(&s));
>  
>  	return buf;
>  }