[PATCH] drm/radeon: validate ATRM return buffer type and length

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

radeon_atrm_call() copies the ACPI ATRM method return data without
checking that the returned object is actually a buffer or that its
length fits within the caller-provided size.  If the ATRM method
returns a non-buffer object type or an oversized buffer, the memcpy
writes past the destination bounds.

Add a NULL pointer check and ACPI_TYPE_BUFFER type validation before
accessing the buffer fields, and clamp the copy length to the
requested size.  This matches the validation already present in the
amdgpu counterpart amdgpu_atrm_call().

Fixes: c61e2775873f ("drm/radeon: split ATRM support out from the ATPX handler (v3)")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 drivers/gpu/drm/radeon/radeon_bios.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_bios.c b/drivers/gpu/drm/radeon/radeon_bios.c
index 1da6bf1c17ff3..579ba1c1f23a4 100644
--- a/drivers/gpu/drm/radeon/radeon_bios.c
+++ b/drivers/gpu/drm/radeon/radeon_bios.c
@@ -183,8 +183,13 @@ static int radeon_atrm_call(acpi_handle atrm_handle, uint8_t *bios,
 	}
 
 	obj = (union acpi_object *)buffer.pointer;
-	memcpy(bios+offset, obj->buffer.pointer, obj->buffer.length);
-	len = obj->buffer.length;
+	if (!obj || obj->type != ACPI_TYPE_BUFFER) {
+		kfree(buffer.pointer);
+		return -EINVAL;
+	}
+
+	len = min_t(size_t, obj->buffer.length, len);
+	memcpy(bios + offset, obj->buffer.pointer, len);
 	kfree(buffer.pointer);
 	return len;
 }
-- 
2.47.3