[PATCH] 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 clamping each memcpy length to the size of its destination
field with min_t(u32, buffer.length, sizeof(cap_hdr->field)).

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 | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c
index 6283105bb0e8..0219347cd78f 100644
--- a/drivers/acpi/pfr_update.c
+++ b/drivers/acpi/pfr_update.c
@@ -161,24 +161,28 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr,
 	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,
-	       out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length);
+	       min_t(u32, out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length,
+		     sizeof(cap_hdr->code_type)));
 	cap_hdr->fw_version =
 		out_obj->package.elements[CAP_FW_VER_IDX].integer.value;
 	cap_hdr->code_rt_version =
 		out_obj->package.elements[CAP_CODE_RT_VER_IDX].integer.value;
 	memcpy(&cap_hdr->drv_type,
 	       out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.pointer,
-	       out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length);
+	       min_t(u32, out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length,
+		     sizeof(cap_hdr->drv_type)));
 	cap_hdr->drv_rt_version =
 		out_obj->package.elements[CAP_DRV_RT_VER_IDX].integer.value;
 	cap_hdr->drv_svn =
 		out_obj->package.elements[CAP_DRV_SVN_IDX].integer.value;
 	memcpy(&cap_hdr->platform_id,
 	       out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.pointer,
-	       out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length);
+	       min_t(u32, out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length,
+		     sizeof(cap_hdr->platform_id)));
 	memcpy(&cap_hdr->oem_id,
 	       out_obj->package.elements[CAP_OEM_ID_IDX].buffer.pointer,
-	       out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length);
+	       min_t(u32, out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length,
+		     sizeof(cap_hdr->oem_id)));
 	cap_hdr->oem_info_len =
 		out_obj->package.elements[CAP_OEM_INFO_IDX].buffer.length;
 
-- 
2.55.0