Re: [PATCH] thermal: core: Move initial num_trips assignment before memcpy()

[Lukasz Luba]

Hi Nathan,

On 2/27/24 00:54, Nathan Chancellor wrote:

When booting a CONFIG_FORTIFY_SOURCE=y kernel compiled with a toolchain
that supports __counted_by() (such as clang-18 and newer), there is a
panic on boot:

   [    2.913770] memcpy: detected buffer overflow: 72 byte write of buffer 
size 0
   [    2.920834] WARNING: CPU: 2 PID: 1 at lib/string_helpers.c:1027 
__fortify_report+0x5c/0x74
   ...
   [    3.039208] Call trace:
   [    3.041643]  __fortify_report+0x5c/0x74
   [    3.045469]  __fortify_panic+0x18/0x20
   [    3.049209]  thermal_zone_device_register_with_trips+0x4c8/0x4f8

This panic occurs because trips is counted by num_trips but num_trips is
assigned after the call to memcpy(), so the fortify checks think the
buffer size is zero because tz was allocated with kzalloc().

I don't know this tool (yet), but this description doesn't help to
understand it better.

In the memcpy() the 'num_trips' is used not 'tz->num_trips' and
'num_trips' is set in the function argument.

Move the num_trips assignment before the memcpy() to resolve the panic
and ensure that the fortify checks work properly.

I don't see how this change can impact the code not this tool.

Fixes: 9b0a62758665 ("thermal: core: Store zone trips table in struct 
thermal_zone_device")
Signed-off-by: Nathan Chancellor <nat...@kernel.org>
---
  drivers/thermal/thermal_core.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index bb21f78b4bfa..1eabc8ebe27d 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -1354,8 +1354,8 @@ thermal_zone_device_register_with_trips(const char *type,

tz->device.class = thermal_class;

        tz->devdata = devdata;
-       memcpy(tz->trips, trips, num_trips * sizeof(*trips));
        tz->num_trips = num_trips;
+       memcpy(tz->trips, trips, num_trips * sizeof(*trips));

thermal_set_delay_jiffies(&tz->passive_delay_jiffies, passive_delay);

        thermal_set_delay_jiffies(&tz->polling_delay_jiffies, polling_delay);

---
base-commit: a85739c8c6894c3b9ff860e79e91db44cb59bd63
change-id: 20240226-thermal-fix-fortify-panic-num_trips-5f94094fb963

Best regards,

Maybe it reports different issue. There is some corner case when the
num_trips is 0. It's called from
thermal_tripless_zone_device_register().
Does your code is triggered from that function?
(you've cut the call stack so I cannot see this there)

Regards,
Lukasz