[PATCH] cpufreq: pcc: fix use-after-free and double free in _OSC evaluation

[Hongyan Xu <getshell@seu.edu.cn>]

pcc_cpufreq_do_osc() uses a two-phase _OSC evaluation and frees the
output buffer returned by the first acpi_evaluate_object() call before
reusing the same acpi_buffer in the second call.

However, output.pointer and output.length are not reset after the
first kfree(). That can make the second acpi_evaluate_object() treat
the stale metadata as a caller-provided buffer and write into freed
memory. The shared out_free path can then free the same pointer again.

Reset the output buffer state after the first kfree() so ACPICA
allocates a fresh buffer for the second _OSC evaluation.

Fixes: 0f1d683fb35d ("[CPUFREQ] Processor Clocking Control interface driver")
Issue found using a prototype static analysis tool
and confirmed by code review.

Signed-off-by: Hongyan Xu <getshell@seu.edu.cn>
Signed-off-by: Slavin Liu <220245772@seu.edu.cn>
---
 drivers/cpufreq/pcc-cpufreq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c
index ac2e90a65f0c..a355ec4f3dd4 100644
--- a/drivers/cpufreq/pcc-cpufreq.c
+++ b/drivers/cpufreq/pcc-cpufreq.c
@@ -352,6 +352,8 @@ static int __init pcc_cpufreq_do_osc(acpi_handle *handle)
 	}
 
 	kfree(output.pointer);
+	output.pointer = NULL;
+	output.length = ACPI_ALLOCATE_BUFFER;
 	capabilities[0] = 0x0;
 	capabilities[1] = 0x1;
 
-- 
2.50.1.windows.1