[PATCH 1/1] time/jiffies: Fix conversion breakage on systems where USER_HZ < HZ

[PATCH 1/1] time/jiffies: Fix conversion breakage on systems where USER_HZ < HZ

[Gerd Rausch]

Conversion from user_hz to jiffies broke with
commit 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")

because the old overflow check in do_proc_dointvec_userhz_jiffies_conv()
to see if "*u_ptr" was too large got replaced by an unconditional:
     +    if (USER_HZ < HZ)
     +        return -EINVAL;

which will always be true on platforms with "USER_HZ < HZ".

We shouldn't need this extra check anyway, because clock_t_to_jiffies()
returns ULONG_MAX for the overflow case:
     if (x >= ~0UL / (HZ / USER_HZ))
         return ~0UL;

and proc_int_u2k_conv_uop() checks for "> INT_MAX" after conversion:
     if (u > (ulong) INT_MAX)
         return -EINVAL;

Fixes: 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
Reported-by: Colm Harrington <colm.harrington@oracle.com>
Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
---
  kernel/time/jiffies.c | 2 --
  1 file changed, 2 deletions(-)

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index a5c7d15fce72..9daf8c5d9687 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -256,8 +256,6 @@ EXPORT_SYMBOL(proc_dointvec_jiffies);
  int proc_dointvec_userhz_jiffies(const struct ctl_table *table, int dir,
  				 void *buffer, size_t *lenp, loff_t *ppos)
  {
-	if (SYSCTL_USER_TO_KERN(dir) && USER_HZ < HZ)
-		return -EINVAL;
  	return proc_dointvec_conv(table, dir, buffer, lenp, ppos,
  				  do_proc_int_conv_userhz_jiffies);
  }
-- 
2.39.3

Re: [PATCH 1/1] time/jiffies: Fix conversion breakage on systems where USER_HZ < HZ

[Joel Granados]

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On Wed, Feb 25, 2026 at 03:37:49PM -0800, Gerd Rausch wrote:
> Conversion from user_hz to jiffies broke with
The internal kernel conversion itself is unchanged, it is informing user
space about this conversion that broke. Right? In other words, you get
an error when you read a sysctl file instead of an incorrect converted
value.

> commit 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
> 
> because the old overflow check in do_proc_dointvec_userhz_jiffies_conv()
> to see if "*u_ptr" was too large got replaced by an unconditional:
>     +    if (USER_HZ < HZ)
>     +        return -EINVAL;
> 
> which will always be true on platforms with "USER_HZ < HZ".
> 
> We shouldn't need this extra check anyway, because clock_t_to_jiffies()
> returns ULONG_MAX for the overflow case:
>     if (x >= ~0UL / (HZ / USER_HZ))
>         return ~0UL;
> 
> and proc_int_u2k_conv_uop() checks for "> INT_MAX" after conversion:
>     if (u > (ulong) INT_MAX)
>         return -EINVAL;
> 
> Fixes: 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
> Reported-by: Colm Harrington <colm.harrington@oracle.com>
> Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
> ---
>  kernel/time/jiffies.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
> index a5c7d15fce72..9daf8c5d9687 100644
> --- a/kernel/time/jiffies.c
> +++ b/kernel/time/jiffies.c
> @@ -256,8 +256,6 @@ EXPORT_SYMBOL(proc_dointvec_jiffies);
>  int proc_dointvec_userhz_jiffies(const struct ctl_table *table, int dir,
>  				 void *buffer, size_t *lenp, loff_t *ppos)
>  {
> -	if (SYSCTL_USER_TO_KERN(dir) && USER_HZ < HZ)
> -		return -EINVAL;
This fix looks good. I'll put it in next to see if it breaks anything.

>  	return proc_dointvec_conv(table, dir, buffer, lenp, ppos,
>  				  do_proc_int_conv_userhz_jiffies);
>  }
> -- 
> 2.39.3
> 

How did you see the bug? Was it trying to read a sysctl file?

Best
-- 

Joel Granados

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Re: [PATCH 1/1] time/jiffies: Fix conversion breakage on systems where USER_HZ < HZ

[Joel Granados]

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On Wed, Feb 25, 2026 at 03:37:49PM -0800, Gerd Rausch wrote:
> Conversion from user_hz to jiffies broke with
> commit 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
> 
> because the old overflow check in do_proc_dointvec_userhz_jiffies_conv()
> to see if "*u_ptr" was too large got replaced by an unconditional:
>     +    if (USER_HZ < HZ)
>     +        return -EINVAL;
> 
> which will always be true on platforms with "USER_HZ < HZ".
> 
> We shouldn't need this extra check anyway, because clock_t_to_jiffies()
> returns ULONG_MAX for the overflow case:
>     if (x >= ~0UL / (HZ / USER_HZ))
>         return ~0UL;
> 
> and proc_int_u2k_conv_uop() checks for "> INT_MAX" after conversion:
>     if (u > (ulong) INT_MAX)
>         return -EINVAL;
> 
> Fixes: 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
> Reported-by: Colm Harrington <colm.harrington@oracle.com>
> Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
I changed the message of the patch a bit. You can take a look here [1] 

Best

[1] https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git/commit/?h=sysctl-next&id=a17a86da1c90b62866bf2f45560510f2f6f18503

-- 

Joel Granados

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Re: [PATCH 1/1] time/jiffies: Fix conversion breakage on systems where USER_HZ < HZ

[Gerd Rausch]

Hi Joel,

On 2026-02-27 06:31, Joel Granados wrote:
> On Wed, Feb 25, 2026 at 03:37:49PM -0800, Gerd Rausch wrote:
>> Conversion from user_hz to jiffies broke with
> The internal kernel conversion itself is unchanged, it is informing user
> space about this conversion that broke. Right? In other words, you get
> an error when you read a sysctl file instead of an incorrect converted
> value.
> 
>> commit 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
>>
>> because the old overflow check in do_proc_dointvec_userhz_jiffies_conv()
>> to see if "*u_ptr" was too large got replaced by an unconditional:
>>      +    if (USER_HZ < HZ)
>>      +        return -EINVAL;
>>
>> which will always be true on platforms with "USER_HZ < HZ".
>>
>> We shouldn't need this extra check anyway, because clock_t_to_jiffies()
>> returns ULONG_MAX for the overflow case:
>>      if (x >= ~0UL / (HZ / USER_HZ))
>>          return ~0UL;
>>
>> and proc_int_u2k_conv_uop() checks for "> INT_MAX" after conversion:
>>      if (u > (ulong) INT_MAX)
>>          return -EINVAL;
>>
>> Fixes: 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
>> Reported-by: Colm Harrington <colm.harrington@oracle.com>
>> Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
>> ---
>>   kernel/time/jiffies.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
>> index a5c7d15fce72..9daf8c5d9687 100644
>> --- a/kernel/time/jiffies.c
>> +++ b/kernel/time/jiffies.c
>> @@ -256,8 +256,6 @@ EXPORT_SYMBOL(proc_dointvec_jiffies);
>>   int proc_dointvec_userhz_jiffies(const struct ctl_table *table, int dir,
>>   				 void *buffer, size_t *lenp, loff_t *ppos)
>>   {
>> -	if (SYSCTL_USER_TO_KERN(dir) && USER_HZ < HZ)
>> -		return -EINVAL;
> This fix looks good. I'll put it in next to see if it breaks anything.
> 
>>   	return proc_dointvec_conv(table, dir, buffer, lenp, ppos,
>>   				  do_proc_int_conv_userhz_jiffies);
>>   }
>> -- 
>> 2.39.3
>>
> 
> How did you see the bug? Was it trying to read a sysctl file?
> 

My colleague Colm (mentioned under "Reported-by:") saw it:
--------%<--------%<--------%<--------%<--------%<--------%<--------
[root@somemachine]# sysctl -w net.ipv4.neigh.re1.locktime=0
sysctl: setting key "net.ipv4.neigh.re1.locktime": Invalid argument
--------%<--------%<--------%<--------%<--------%<--------%<--------

Thanks,

   Gerd

Re: [PATCH 1/1] time/jiffies: Fix conversion breakage on systems where USER_HZ < HZ

[Gerd Rausch]

Hi Joel,

On 2026-02-27 07:03, Joel Granados wrote:
> On Wed, Feb 25, 2026 at 03:37:49PM -0800, Gerd Rausch wrote:
>> Conversion from user_hz to jiffies broke with
>> commit 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
>>
>> because the old overflow check in do_proc_dointvec_userhz_jiffies_conv()
>> to see if "*u_ptr" was too large got replaced by an unconditional:
>>      +    if (USER_HZ < HZ)
>>      +        return -EINVAL;
>>
>> which will always be true on platforms with "USER_HZ < HZ".
>>
>> We shouldn't need this extra check anyway, because clock_t_to_jiffies()
>> returns ULONG_MAX for the overflow case:
>>      if (x >= ~0UL / (HZ / USER_HZ))
>>          return ~0UL;
>>
>> and proc_int_u2k_conv_uop() checks for "> INT_MAX" after conversion:
>>      if (u > (ulong) INT_MAX)
>>          return -EINVAL;
>>
>> Fixes: 2dc164a48e6fd ("sysctl: Create converter functions with two new macros")
>> Reported-by: Colm Harrington <colm.harrington@oracle.com>
>> Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
> I changed the message of the patch a bit. You can take a look here [1]
> 
> Best
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git/commit/?h=sysctl-next&id=a17a86da1c90b62866bf2f45560510f2f6f18503
> 

Looks good to me.

Thanks for adding this fix,

   Gerd