[PATCH v3] tracing/osnoise: Replace kmalloc + copy_from_user with memdup_user_nul

[Thorsten Blum <thorsten.blum@linux.dev>]

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.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
Changes in v3:
- Use memdup_user_nul() instead of memdup_user() because of the fix a2501032de0d
  ("tracing/osnoise: Fix slab-out-of-bounds in _parse_integer_limit()")
- Link to v2: https://lore.kernel.org/lkml/20250925211736.81737-1-thorsten.blum@linux.dev/

Changes in v2:
- Rebase to apply to master and linux-next
- Explicitly include linux/string.h
- Link to v1: https://lore.kernel.org/lkml/20250905192116.554018-2-thorsten.blum@linux.dev/
---
 kernel/trace/trace_osnoise.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index dc734867f0fc..26d0c99125f5 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/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
@@ -2325,13 +2326,9 @@ 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;
-- 
2.51.0