[PATCH] thermal: Fix UUID string comparison in current_uuid_store()

[PATCH] thermal: Fix UUID string comparison in current_uuid_store()

[Kaushlendra Kumar]

Use strlen() for UUID matching instead of sizeof() to ensure
correct comparison of supported UUIDs. sizeof() returns pointer
size instead of actual string length, causing incomplete UUID
matching.

Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
---
 drivers/thermal/intel/int340x_thermal/int3400_thermal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/thermal/intel/int340x_thermal/int3400_thermal.c b/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
index 908cc1bf57f1..236003d12dc7 100644
--- a/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
+++ b/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
@@ -199,7 +199,7 @@ static ssize_t current_uuid_store(struct device *dev,
 
 	for (i = 0; i < INT3400_THERMAL_MAXIMUM_UUID; ++i) {
 		if (!strncmp(buf, int3400_thermal_uuids[i],
-			     sizeof(int3400_thermal_uuids[i]) - 1)) {
+			     strlen(int3400_thermal_uuids[i]))) {
 			/*
 			 * If we have a list of supported UUIDs, make sure
 			 * this one is supported.
-- 
2.34.1

Re: [PATCH] thermal: Fix UUID string comparison in current_uuid_store()

[Rafael J. Wysocki]

On Fri, Oct 17, 2025 at 9:29 AM Kaushlendra Kumar
<kaushlendra.kumar@intel.com> wrote:
>
> Use strlen() for UUID matching instead of sizeof() to ensure
> correct comparison of supported UUIDs. sizeof() returns pointer
> size instead of actual string length, causing incomplete UUID
> matching.
>
> Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
> ---
>  drivers/thermal/intel/int340x_thermal/int3400_thermal.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/intel/int340x_thermal/int3400_thermal.c b/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
> index 908cc1bf57f1..236003d12dc7 100644
> --- a/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
> +++ b/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
> @@ -199,7 +199,7 @@ static ssize_t current_uuid_store(struct device *dev,
>
>         for (i = 0; i < INT3400_THERMAL_MAXIMUM_UUID; ++i) {

Exercise for the reader: Add a printk() here to print
sizeof(int3400_thermal_uuids[i]) and see what number gets printed.

>                 if (!strncmp(buf, int3400_thermal_uuids[i],
> -                            sizeof(int3400_thermal_uuids[i]) - 1)) {
> +                            strlen(int3400_thermal_uuids[i]))) {
>                         /*
>                          * If we have a list of supported UUIDs, make sure
>                          * this one is supported.
> --

Re: [PATCH] thermal: Fix UUID string comparison in current_uuid_store()

[Rafael J. Wysocki]

On Wed, Oct 29, 2025 at 5:40 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Fri, Oct 17, 2025 at 9:29 AM Kaushlendra Kumar
> <kaushlendra.kumar@intel.com> wrote:
> >
> > Use strlen() for UUID matching instead of sizeof() to ensure
> > correct comparison of supported UUIDs. sizeof() returns pointer
> > size instead of actual string length, causing incomplete UUID
> > matching.
> >
> > Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
> > ---
> >  drivers/thermal/intel/int340x_thermal/int3400_thermal.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/thermal/intel/int340x_thermal/int3400_thermal.c b/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
> > index 908cc1bf57f1..236003d12dc7 100644
> > --- a/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
> > +++ b/drivers/thermal/intel/int340x_thermal/int3400_thermal.c
> > @@ -199,7 +199,7 @@ static ssize_t current_uuid_store(struct device *dev,
> >
> >         for (i = 0; i < INT3400_THERMAL_MAXIMUM_UUID; ++i) {
>
> Exercise for the reader: Add a printk() here to print
> sizeof(int3400_thermal_uuids[i]) and see what number gets printed.

It is 8, but note that comparing the first 7 characters is practically
sufficient to distinguish all of the UUIDs in int3400_thermal_uuids[]
from each other.

Also, this change would alter the kernel ABI, possibly confusing users
who might notice that the first 7 characters mattered and might start
to rely on that.

If you want to clean up that piece of code, please change it to pass a
symbol representing the number 7 as the last argument to strncmp(),
but that is as much as can be done here.

> >                 if (!strncmp(buf, int3400_thermal_uuids[i],
> > -                            sizeof(int3400_thermal_uuids[i]) - 1)) {
> > +                            strlen(int3400_thermal_uuids[i]))) {
> >                         /*
> >                          * If we have a list of supported UUIDs, make sure
> >                          * this one is supported.
> > --

RE: [PATCH] thermal: Fix UUID string comparison in current_uuid_store()

[Kumar, Kaushlendra]

On Wed, Oct 29, 2025 at 5:40 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> Also, this change would alter the kernel ABI, possibly confusing users who might notice that the first 7 characters mattered and might start to rely on that.
> 
> If you want to clean up that piece of code, please change it to pass a symbol representing the number 7 as the last argument to strncmp(), but that is as much as can be done here.

You're right about the ABI concern. I have sent  a v2 patch that uses a 
symbolic constant for the 7-character comparison to maintain existing behavior 

Thanks for the Review!

Kaushlendra