[PATCH 5/6] thunderbolt: limit XDomain response copy to actual frame size

[Michael Bommarito <michael.bommarito@gmail.com>]

tb_xdomain_copy() copies req->response_size bytes from the received
packet buffer regardless of the actual frame size.  When a short
response arrives, this reads past the valid frame data in the DMA
pool buffer into stale contents from previous transactions.

Use the minimum of frame size and expected response size for the
copy length.

Fixes: cdae7c07e3e3 ("thunderbolt: Add support for XDomain properties")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
The DMA pool buffer (ctl.c:340) is always 256 bytes, so a short
frame does not cause an out-of-bounds read from the buffer itself.
The real impact is that bytes past the valid frame contain stale
data from previous DMA transactions, which are copied into the
response struct and interpreted as protocol fields.

Confirmed on QEMU (7.1.0-rc3).

 drivers/thunderbolt/xdomain.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/xdomain.c b/drivers/thunderbolt/xdomain.c
index 9d54e3ccc8278..1fd1cf4295a2a 100644
--- a/drivers/thunderbolt/xdomain.c
+++ b/drivers/thunderbolt/xdomain.c
@@ -123,7 +123,9 @@ static bool tb_xdomain_match(const struct tb_cfg_request *req,
 static bool tb_xdomain_copy(struct tb_cfg_request *req,
 			    const struct ctl_pkg *pkg)
 {
-	memcpy(req->response, pkg->buffer, req->response_size);
+	size_t len = min_t(size_t, pkg->frame.size, req->response_size);
+
+	memcpy(req->response, pkg->buffer, len);
 	req->result.err = 0;
 	return true;
 }
-- 
2.53.0