[PATCH v2] cpufreq: pcc: fix use-after-free and double free in _OSC evaluation

[Yuho Choi]

pcc_cpufreq_do_osc() calls acpi_evaluate_object() twice for the
two-phase _OSC negotiation. Between the two calls it freed
output.pointer but left output.length unchanged. Since
acpi_evaluate_object() treats a non-zero length with a non-NULL
pointer as an existing buffer to write into, the second call wrote
into freed memory (use-after-free). The subsequent kfree(output.pointer)
at out_free then freed the same pointer a second time (double free).

Reset output.pointer to NULL and output.length to ACPI_ALLOCATE_BUFFER
after freeing the first result, so ACPICA allocates a fresh buffer for
each phase independently.

Fixes: 0f1d683fb35d ("[CPUFREQ] Processor Clocking Control interface driver")
Signed-off-by: Yuho Choi <dbgh9129@xxxxxxxxx>
---

Changes in v1:
  - Drop spurious #include "acpi/actypes.h" (Zhongqiu Han)
  - Keep kfree() between the two calls and reset output.pointer = NULL
    and output.length = ACPI_ALLOCATE_BUFFER

 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 ac2e90a65f0c4..a355ec4f3dd4c 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 (Apple Git-155)