[PATCH] platform/x86: hp-wmi: fix heap OOB read and memory corruption in hp_wmi_perform_query()

hp_wmi_perform_query() evaluates an ACPI WMI method and expects a
struct bios_return header in the returned buffer. However, it only
checks that the ACPI object type is ACPI_TYPE_BUFFER without verifying
that obj->buffer.length is at least sizeof(*bios_return) (8 bytes).

If the firmware or ACPI method returns a buffer shorter than 8 bytes:
1. bios_return->return_code at offset 4 reads out of bounds from the
   allocated ACPI buffer slab.
2. If return_code evaluates to 0 and outsize is non-zero,
   (int)(obj->buffer.length - sizeof(*bios_return)) evaluates to a
   negative integer (e.g. -8 for a 0-length buffer).
   actual_outsize is set to this negative value and passed to
   memcpy(buffer, ..., actual_outsize), where the signed negative value
   is cast to size_t (e.g. 0xfffffffffffffff8), attempting to copy ~18
   Exabytes and triggering an immediate kernel crash.
   Additionally, memset(buffer + actual_outsize, ...) performs an
   out-of-bounds write before buffer.

Fix this by ensuring obj->buffer.length is at least sizeof(*bios_return)
before accessing the return code, and compute actual_outsize safely
using min_t(u32, ...).

Fixes: c3021ea1beee ("hp-wmi: allow setting input and output buffer sizes separately")
Cc: [email protected]
Signed-off-by: Muhammad Bilal <[email protected]>
---
 drivers/platform/x86/hp/hp-wmi.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/hp/hp-wmi.c b/drivers/platform/x86/hp/hp-wmi.c
index 8ba286ed8721..f3cab841afc4 100644
--- a/drivers/platform/x86/hp/hp-wmi.c
+++ b/drivers/platform/x86/hp/hp-wmi.c
@@ -616,8 +616,9 @@ static int hp_wmi_perform_query(int query, enum hp_wmi_command command,
 		goto out_free;
 	}
 
-	if (obj->type != ACPI_TYPE_BUFFER) {
-		pr_warn("query 0x%x returned an invalid object 0x%x\n", query, ret);
+	if (obj->type != ACPI_TYPE_BUFFER ||
+	    obj->buffer.length < sizeof(*bios_return)) {
+		pr_warn("query 0x%x returned wrong type or too small buffer\n", query);
 		ret = -EINVAL;
 		goto out_free;
 	}
@@ -636,7 +637,7 @@ static int hp_wmi_perform_query(int query, enum hp_wmi_command command,
 	if (!outsize)
 		goto out_free;
 
-	actual_outsize = min(outsize, (int)(obj->buffer.length - sizeof(*bios_return)));
+	actual_outsize = min_t(u32, outsize, obj->buffer.length - sizeof(*bios_return));
 	memcpy(buffer, obj->buffer.pointer + sizeof(*bios_return), actual_outsize);
 	memset(buffer + actual_outsize, 0, outsize - actual_outsize);
 
-- 
2.55.0