[PATCH v4 4/4] gpiolib: acpi: fix out-of-bounds pointer arithmetic in acpi_gpio_package_count

[Marco Scardovi <scardracs@disroot.org>]

When counting GPIOs in an ACPI package, encountering a reference or
string causes the element pointer to be advanced by 3 (element += 3)
and then by 1 (element++).

If a malformed ACPI package contains fewer than 4 remaining elements
when a reference or string is processed, this pointer arithmetic
advances the element pointer past the end of the package elements
array. This results in undefined behavior and can cause out-of-bounds
reads.

Fix this by ensuring at least 4 elements remain in the package before
advancing the element pointer, returning -EPROTO if the package
structure is invalid.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Marco Scardovi <scardracs@disroot.org>
---
 drivers/gpio/gpiolib-acpi-core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpio/gpiolib-acpi-core.c b/drivers/gpio/gpiolib-acpi-core.c
index d12dab42a096..b19fd02b64d0 100644
--- a/drivers/gpio/gpiolib-acpi-core.c
+++ b/drivers/gpio/gpiolib-acpi-core.c
@@ -1407,6 +1407,8 @@ static int acpi_gpio_package_count(const union acpi_object *obj)
 		switch (element->type) {
 		case ACPI_TYPE_LOCAL_REFERENCE:
 		case ACPI_TYPE_STRING:
+			if (end - element < 4)
+				return -EPROTO;
 			element += 3;
 			fallthrough;
 		case ACPI_TYPE_INTEGER:
-- 
2.54.0