linux-hardening - [PATCH] thermal: core: Move initial num

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Message-Id: <20240226-thermal-fix-fortify-panic-num_trips-v1-1-accc12a341d7@kernel.org>
Date: Mon, 26 Feb 2024 17:54:58 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: rafael@...nel.org, daniel.lezcano@...aro.org
Cc: rui.zhang@...el.com, lukasz.luba@....com, keescook@...omium.org, 
 gustavoars@...nel.org, morbo@...gle.com, justinstitt@...gle.com, 
 stanislaw.gruszka@...ux.intel.com, linux-pm@...r.kernel.org, 
 linux-hardening@...r.kernel.org, llvm@...ts.linux.dev, 
 patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] thermal: core: Move initial num_trips assignment before
 memcpy()

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().

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

Fixes: 9b0a62758665 ("thermal: core: Store zone trips table in struct thermal_zone_device")
Signed-off-by: Nathan Chancellor <nathan@...nel.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,
-- 
Nathan Chancellor <nathan@...nel.org>