[PATCH 4/6] thunderbolt: validate XDomain request packet size before type cast

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

tb_xdp_handle_request() casts the received packet buffer to
protocol-specific structs without verifying that the allocation
is large enough for the target type.  A peer can send a minimal
XDomain packet that passes the generic header length check but is
shorter than the struct accessed after the cast, causing out-of-
bounds reads from the kmemdup allocation.

Plumb the packet length through xdomain_request_work and validate
it against the expected struct size before each cast.

Fixes: 8e1de7042596 ("thunderbolt: Add support for XDomain lane bonding")
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>
---
Stock KASAN splat reproduced on QEMU (7.1.0-rc3).  A test module
allocates a 32-byte packet (tb_xdp_header only) and casts to
tb_xdp_link_state_change (36 bytes).  The read past the allocation
fires immediately:

  BUG: KASAN: slab-out-of-bounds in
       tb_test_xdp_short_packet_cast_trigger.cold+0x118/0x12d
  Read of size 1 at addr ffff888002110260
  located 0 bytes to the right of allocated 32-byte region

Also exercised over Thunderbolt 4 cable with 258 truncated-packet
injections (PROPERTIES_REQUEST 68 -> 32 bytes).

 drivers/thunderbolt/xdomain.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/thunderbolt/xdomain.c b/drivers/thunderbolt/xdomain.c
index 4099419c74795..9d54e3ccc8278 100644
--- a/drivers/thunderbolt/xdomain.c
+++ b/drivers/thunderbolt/xdomain.c
@@ -55,6 +55,7 @@ static const char * const state_names[] = {
 struct xdomain_request_work {
 	struct work_struct work;
 	struct tb_xdp_header *pkg;
+	size_t pkg_len;
 	struct tb *tb;
 };
 
@@ -733,6 +734,7 @@ static void tb_xdp_handle_request(struct work_struct *work)
 	struct xdomain_request_work *xw = container_of(work, typeof(*xw), work);
 	const struct tb_xdp_header *pkg = xw->pkg;
 	const struct tb_xdomain_header *xhdr = &pkg->xd_hdr;
+	size_t pkg_len = xw->pkg_len;
 	struct tb *tb = xw->tb;
 	struct tb_ctl *ctl = tb->ctl;
 	struct tb_xdomain *xd;
@@ -764,7 +766,7 @@ static void tb_xdp_handle_request(struct work_struct *work)
 	switch (pkg->type) {
 	case PROPERTIES_REQUEST:
 		tb_dbg(tb, "%llx: received XDomain properties request\n", route);
-		if (xd) {
+		if (xd && pkg_len >= sizeof(struct tb_xdp_properties)) {
 			ret = tb_xdp_properties_response(tb, ctl, xd, sequence,
 				(const struct tb_xdp_properties *)pkg);
 		}
@@ -818,7 +820,8 @@ static void tb_xdp_handle_request(struct work_struct *work)
 		tb_dbg(tb, "%llx: received XDomain link state change request\n",
 		       route);
 
-		if (xd && xd->state == XDOMAIN_STATE_BONDING_UUID_HIGH) {
+		if (xd && xd->state == XDOMAIN_STATE_BONDING_UUID_HIGH &&
+		    pkg_len >= sizeof(struct tb_xdp_link_state_change)) {
 			const struct tb_xdp_link_state_change *lsc =
 				(const struct tb_xdp_link_state_change *)pkg;
 
@@ -870,6 +873,7 @@ tb_xdp_schedule_request(struct tb *tb, const struct tb_xdp_header *hdr,
 		kfree(xw);
 		return false;
 	}
+	xw->pkg_len = size;
 	xw->tb = tb_domain_get(tb);
 
 	schedule_work(&xw->work);
-- 
2.53.0