tracing/osnoise: Replace kmalloc + copy_from_user with memdup_user_nul

JIRA: https://issues.redhat.com/browse/RHEL-117873

commit f0c029d
Author: Thorsten Blum <thorsten.blum@linux.dev>
Date:   Wed Oct 1 15:09:07 2025 +0200

    tracing/osnoise: Replace kmalloc + copy_from_user with memdup_user_nul

    Replace kmalloc() followed by copy_from_user() with memdup_user_nul() to
    simplify and improve osnoise_cpus_write(). Remove the manual
    NUL-termination.

    No functional changes intended.

    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Link: https://lore.kernel.org/20251001130907.364673-2-thorsten.blum@linux.dev
    Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Signed-off-by: Tomas Glozar <tglozar@redhat.com>

Author: lenticularis39

kernel/trace/trace_osnoise.c

@@ -24,6 +24,7 @@
 #include <linux/sched/clock.h>
 #include <uapi/linux/sched/types.h>
 #include <linux/sched.h>
+#include <linux/string.h>
 #include "trace.h"
 
 #ifdef CONFIG_X86_LOCAL_APIC
@@ -2331,13 +2332,9 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 	if (count < 1)
 		return 0;
 
-	buf = kmalloc(count + 1, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	if (copy_from_user(buf, ubuf, count))
-		return -EFAULT;
-	buf[count] = '\0';
+	buf = memdup_user_nul(ubuf, count);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
 
 	if (!zalloc_cpumask_var(&osnoise_cpumask_new, GFP_KERNEL))
 		return -ENOMEM;