[PATCH 0/2] Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()

[PATCH 0/2] Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()

[Fushuai Wang]

From: Fushuai Wang <wangfushuai@baidu.com>

Hi,

There are several places use copy_from_user() to copy a string from
userspase, followed by kstrtoXXX() to convert it to a desired type.
This approach requires manually handling NUL-termination and proper
buffer sizing, which is error-prone and unnecessarily complex. The
kernel provides kstrtoXXX_from_user() helpers to copy a string from
userspace and perform the conversion in one step. So use a
kstrtoXXX_from_user() instead of copy_from_user() + kstrtoXXX().

Recent discussion:
https://lore.kernel.org/all/20260112073039.1185-1-fushuai.wang@linux.dev/T/

Fushuai Wang (2):
  sched/debug: Convert copy_from_user() + kstrtouint() to
    kstrtouint_from_user()
  x86/tlb: Convert copy_from_user() + kstrtouint() to
    kstrtouint_from_user()

 arch/x86/mm/tlb.c    | 13 ++++---------
 kernel/sched/debug.c | 14 ++++----------
 2 files changed, 8 insertions(+), 19 deletions(-)

-- 
2.36.1

[PATCH 1/2] sched/debug: Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()

[Fushuai Wang]

From: Fushuai Wang <wangfushuai@baidu.com>

Using kstrtouint_from_user() instead of copy_from_user() + kstrtouint()
makes the code simpler and less error-prone.

Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
---
 kernel/sched/debug.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 41caa22e0680..1091f9046260 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -172,18 +172,12 @@ static const struct file_operations sched_feat_fops = {
 static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
 				   size_t cnt, loff_t *ppos)
 {
-	char buf[16];
 	unsigned int scaling;
+	int ret;
 
-	if (cnt > 15)
-		cnt = 15;
-
-	if (copy_from_user(&buf, ubuf, cnt))
-		return -EFAULT;
-	buf[cnt] = '\0';
-
-	if (kstrtouint(buf, 10, &scaling))
-		return -EINVAL;
+	ret = kstrtouint_from_user(ubuf, cnt, 10, &scaling);
+	if (ret < 0)
+		return ret;
 
 	if (scaling >= SCHED_TUNABLESCALING_END)
 		return -EINVAL;
-- 
2.36.1

Re: [PATCH 1/2] sched/debug: Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()

[Yury Norov]

On Fri, Jan 16, 2026 at 09:17:50PM +0800, Fushuai Wang wrote:
> From: Fushuai Wang <wangfushuai@baidu.com>
> 
> Using kstrtouint_from_user() instead of copy_from_user() + kstrtouint()
> makes the code simpler and less error-prone.
> 
> Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
> ---
>  kernel/sched/debug.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 41caa22e0680..1091f9046260 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -172,18 +172,12 @@ static const struct file_operations sched_feat_fops = {
>  static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
>  				   size_t cnt, loff_t *ppos)
>  {
> -	char buf[16];
>  	unsigned int scaling;
> +	int ret;
>  
> -	if (cnt > 15)
> -		cnt = 15;
> -
> -	if (copy_from_user(&buf, ubuf, cnt))
> -		return -EFAULT;
> -	buf[cnt] = '\0';
> -
> -	if (kstrtouint(buf, 10, &scaling))
> -		return -EINVAL;
> +	ret = kstrtouint_from_user(ubuf, cnt, 10, &scaling);
> +	if (ret < 0)
> +		return ret;

This thing returns 0 on success, so I think you could better do:

        if (ret)
                return ret;

With that, for the series:

Suggested-by: Yury Norov <ynorov@nvidia.com>
Reviewed-by: Yury Norov <ynorov@nvidia.com>

Thanks,
Yury

>  
>  	if (scaling >= SCHED_TUNABLESCALING_END)
>  		return -EINVAL;
> -- 
> 2.36.1
> 

[PATCH 2/2] x86/tlb: Convert copy_from_user() + kstrtouint() to kstrtouint_from_user()

[Fushuai Wang]

From: Fushuai Wang <wangfushuai@baidu.com>

Using kstrtouint_from_user() instead of copy_from_user() + kstrtouint()
makes the code simpler and less error-prone.

Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
---
 arch/x86/mm/tlb.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index f5b93e01e347..5e6a07306214 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1802,17 +1802,12 @@ static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
 static ssize_t tlbflush_write_file(struct file *file,
 		 const char __user *user_buf, size_t count, loff_t *ppos)
 {
-	char buf[32];
-	ssize_t len;
 	int ceiling;
+	int err;
 
-	len = min(count, sizeof(buf) - 1);
-	if (copy_from_user(buf, user_buf, len))
-		return -EFAULT;
-
-	buf[len] = '\0';
-	if (kstrtoint(buf, 0, &ceiling))
-		return -EINVAL;
+	err = kstrtoint_from_user(user_buf, count, 0, &ceiling);
+	if (err)
+		return err;
 
 	if (ceiling < 0)
 		return -EINVAL;
-- 
2.36.1