[PATCH 5.15.y] platform/x86: hp-wmi: fix heap OOB read and memory corruption in hp_wmi_perform_query()

[Sasha Levin <sashal@kernel.org>]

From: Muhammad Bilal <meatuni001@gmail.com>

[ Upstream commit 6dea092b261f04d632411c2be52d13190f5f67b1 ]

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, ...), which is sound specifically because the guard
above already rules out obj->buffer.length being smaller than
sizeof(*bios_return) by the time that subtraction runs.

Fixes: c3021ea1beee ("hp-wmi: allow setting input and output buffer sizes separately")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
Link: https://patch.msgid.link/20260826103012.240453-1-meatuni001@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
[ sashal: Adjusted context for the missing pr_warn() line that upstream replaces. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/platform/x86/hp/hp-wmi.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/hp/hp-wmi.c b/drivers/platform/x86/hp/hp-wmi.c
index 94c358f261411..b56e4121d238f 100644
--- a/drivers/platform/x86/hp/hp-wmi.c
+++ b/drivers/platform/x86/hp/hp-wmi.c
@@ -261,7 +261,9 @@ static int hp_wmi_perform_query(int query, enum hp_wmi_command command,
 	if (!obj)
 		return -EINVAL;
 
-	if (obj->type != ACPI_TYPE_BUFFER) {
+	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;
 	}
@@ -280,7 +282,7 @@ 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);
 
-- 
2.53.0