linux-kernel - Re: [PATCH] device_cgroup: Replace strcpy/sprintf in set

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Message-Id: <FE3AAB5A-9AB9-49B6-BB67-FCB97CD5AF29@linux.dev>
Date: Fri, 31 Oct 2025 16:23:02 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: David Laight <david.laight.linux@...il.com>
Cc: Paul Moore <paul@...l-moore.com>,
 James Morris <jmorris@...ei.org>,
 "Serge E. Hallyn" <serge@...lyn.com>,
 linux-security-module@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] device_cgroup: Replace strcpy/sprintf in set_majmin

On 31. Oct 2025, at 13:59, David Laight wrote:
> Even if ex->major can be ~0 there are much cleaner ways of writing this code.

Thanks for pointing this out. Looking at the bigger picture makes it
clear that most of the code can actually be removed. What do you think
of this change?

Thanks,
Thorsten

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index a41f558f6fdd..cb845b1fad6b 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -244,7 +244,6 @@ static void devcgroup_css_free(struct cgroup_subsys_state *css)
#define DEVCG_DENY 2
#define DEVCG_LIST 3

-#define MAJMINLEN 13
#define ACCLEN 4

static void set_access(char *acc, short access)
@@ -270,19 +269,11 @@ static char type_to_char(short type)
	return 'X';
}

-static void set_majmin(char *str, unsigned m)
-{
-	if (m == ~0)
-		strscpy(str, "*", MAJMINLEN);
-	else
-		snprintf(str, MAJMINLEN, "%u", m);
-}
-
static int devcgroup_seq_show(struct seq_file *m, void *v)
{
	struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
	struct dev_exception_item *ex;
-	char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
+	char acc[ACCLEN];

	rcu_read_lock();
	/*
@@ -293,17 +284,12 @@ static int devcgroup_seq_show(struct seq_file *m, void *v)
	 */
	if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
		set_access(acc, DEVCG_ACC_MASK);
-		set_majmin(maj, ~0);
-		set_majmin(min, ~0);
-		seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
-			   maj, min, acc);
+		seq_printf(m, "%c *:* %s\n", type_to_char(DEVCG_DEV_ALL), acc);
	} else {
		list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
			set_access(acc, ex->access);
-			set_majmin(maj, ex->major);
-			set_majmin(min, ex->minor);
-			seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
-				   maj, min, acc);
+			seq_printf(m, "%c %u:%u %s\n", type_to_char(ex->type),
+				   ex->major, ex->minor, acc);
		}
	}
	rcu_read_unlock();