[PATCH v2] ACPI: pfr_update: fix stack buffer overflow in query_capability()

query_capability() copies four ACPI buffer objects returned by the
firmware _DSM into fixed-size u8[16] fields in struct
pfru_update_cap_info using memcpy with the firmware-supplied length:

  memcpy(&cap_hdr->code_type,
         elements[CAP_CODE_TYPE_IDX].buffer.pointer,
         elements[CAP_CODE_TYPE_IDX].buffer.length);

The same pattern repeats for drv_type, platform_id, and oem_id.
If the firmware returns buffer.length > 16 for any of these fields,
memcpy writes past the destination array.

struct pfru_update_cap_info is stack-allocated in pfru_ioctl().
Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports
are generated when a DSM returns 64-byte buffers, with writes reaching
44 bytes past the end of cap_hdr's [64, 156) frame window into
adjacent stack redzones.

Fix by validating each buffer length against its destination field
size before copying, and returning -EINVAL if the firmware supplies
an oversized buffer.

Fixes: 0db89fa243e5 ("ACPI: Introduce Platform Firmware Runtime Update device driver")
Cc: [email protected]
Signed-off-by: Anirudh Prasad <[email protected]>
---
 drivers/acpi/pfr_update.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c
index 6283105bb0e8..e14e053cea44 100644
--- a/drivers/acpi/pfr_update.c
+++ b/drivers/acpi/pfr_update.c
@@ -158,6 +158,14 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr,
 		goto free_acpi_buffer;
 	}
 
+	if (out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length > sizeof(cap_hdr->code_type) ||
+	    out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length > sizeof(cap_hdr->drv_type) ||
+	    out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length > sizeof(cap_hdr->platform_id) ||
+	    out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length > sizeof(cap_hdr->oem_id)) {
+		ret = -EINVAL;
+		goto free_acpi_buffer;
+	}
+
 	cap_hdr->update_cap = out_obj->package.elements[CAP_UPDATE_IDX].integer.value;
 	memcpy(&cap_hdr->code_type,
 	       out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.pointer,
-- 
2.55.0