[PATCH] iio: adc: pac1934: validate ACPI _DSM return type and bounds

[Tristan Madani <tristmd@gmail.com>]

pac1934_acpi_parse_channel_config() calls acpi_evaluate_dsm() four
times to read channel configuration but does not validate the returned
object type or array bounds:

  1. No check that the returned object is ACPI_TYPE_PACKAGE.  If
     firmware returns a different type, accessing rez->package.count
     and rez->package.elements on a non-package object produces
     unpredictable values.

  2. The loop bounds use rez->package.count directly without capping
     to PAC1934_MAX_NUM_CHANNELS (4).  A package with more elements
     than expected causes writes past the fixed-size labels[],
     shunts[], and active_channels[] arrays.

  3. The bipolar and sample rate DSM calls access elements[0] without
     verifying package.count >= 1.

Add ACPI_TYPE_PACKAGE validation after each acpi_evaluate_dsm() call,
cap loop iterations to PAC1934_MAX_NUM_CHANNELS, and verify package
count >= 1 before accessing elements[0].

Fixes: 0fb528c8255b ("iio: adc: adding support for PAC193x")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 drivers/iio/adc/pac1934.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/pac1934.c b/drivers/iio/adc/pac1934.c
index de59dc27c4405..43c4705c27be7 100644
--- a/drivers/iio/adc/pac1934.c
+++ b/drivers/iio/adc/pac1934.c
@@ -1101,8 +1101,13 @@ static int pac1934_acpi_parse_channel_config(struct i2c_client *client,
 	rez = acpi_evaluate_dsm(handle, &guid, 0, PAC1934_ACPI_GET_NAMES_AND_MOHMS_VALS, NULL);
 	if (!rez)
 		return -EINVAL;
+	if (rez->type != ACPI_TYPE_PACKAGE) {
+		ACPI_FREE(rez);
+		return -EINVAL;
+	}
 
-	for (i = 0; i < rez->package.count; i += 2) {
+	for (i = 0; i + 1 < rez->package.count &&
+	     i / 2 < PAC1934_MAX_NUM_CHANNELS; i += 2) {
 		idx = i / 2;
 		info->labels[idx] =
 			devm_kmemdup(dev, rez->package.elements[i].string.pointer,
@@ -1130,7 +1135,13 @@ static int pac1934_acpi_parse_channel_config(struct i2c_client *client,
 		return 0;
 	}
 
-	for (i = 0; i < rez->package.count; i++) {
+	if (rez->type != ACPI_TYPE_PACKAGE) {
+		ACPI_FREE(rez);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < rez->package.count &&
+	     i < PAC1934_MAX_NUM_CHANNELS; i++) {
 		idx = i;
 		info->shunts[idx] = rez->package.elements[i].integer.value;
 		info->active_channels[idx] = (info->shunts[idx] != 0);
@@ -1141,6 +1152,10 @@ static int pac1934_acpi_parse_channel_config(struct i2c_client *client,
 	rez = acpi_evaluate_dsm(handle, &guid, 1, PAC1934_ACPI_GET_BIPOLAR_SETTINGS, NULL);
 	if (!rez)
 		return -EINVAL;
+	if (rez->type != ACPI_TYPE_PACKAGE || rez->package.count < 1) {
+		ACPI_FREE(rez);
+		return -EINVAL;
+	}
 
 	bi_dir_mask = rez->package.elements[0].integer.value;
 	info->bi_dir[0] = ((bi_dir_mask & (1 << 3)) | (bi_dir_mask & (1 << 7))) != 0;
@@ -1153,6 +1168,10 @@ static int pac1934_acpi_parse_channel_config(struct i2c_client *client,
 	rez = acpi_evaluate_dsm(handle, &guid, 1, PAC1934_ACPI_GET_SAMP, NULL);
 	if (!rez)
 		return -EINVAL;
+	if (rez->type != ACPI_TYPE_PACKAGE || rez->package.count < 1) {
+		ACPI_FREE(rez);
+		return -EINVAL;
+	}
 
 	info->sample_rate_value = rez->package.elements[0].integer.value;
 
-- 
2.47.3