If receiving a reply for an MST down request message times out, the
thread receiving the reply in drm_dp_mst_handle_down_rep() could try to
dereference the drm_dp_sideband_msg_tx txmsg request message after the
thread waiting for the reply - calling drm_dp_mst_wait_tx_reply() - has
timed out and freed txmsg, hence leading to a use-after-free in
drm_dp_mst_handle_down_rep().
Prevent the above by holding the drm_dp_mst_topology_mgr::qlock in
drm_dp_mst_handle_down_rep() for the whole duration txmsg is looked up
from the request list and dereferenced.
v2: Fix unlocking mgr->qlock after verify_rx_request_type() fails.
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
---
drivers/gpu/drm/display/drm_dp_mst_topology.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 6ec8680998d5a..ab21855d5c0f7 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -3984,9 +3984,9 @@ static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
/* find the message */
mutex_lock(&mgr->qlock);
+
txmsg = list_first_entry_or_null(&mgr->tx_msg_downq,
struct drm_dp_sideband_msg_tx, next);
- mutex_unlock(&mgr->qlock);
/* Were we actually expecting a response, and from this mstb? */
if (!txmsg || txmsg->dst != mstb) {
@@ -3995,11 +3995,17 @@ static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
hdr = &msg->initial_hdr;
drm_dbg_kms(mgr->dev, "Got MST reply with no msg %p %d %d %02x %02x\n",
mstb, hdr->seqno, hdr->lct, hdr->rad[0], msg->msg[0]);
+
+ mutex_unlock(&mgr->qlock);
+
goto out_clear_reply;
}
- if (!verify_rx_request_type(mgr, txmsg, msg))
+ if (!verify_rx_request_type(mgr, txmsg, msg)) {
+ mutex_unlock(&mgr->qlock);
+
goto out_clear_reply;
+ }
drm_dp_sideband_parse_reply(mgr, msg, &txmsg->reply);
@@ -4013,9 +4019,9 @@ static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
txmsg->reply.u.nak.nak_data);
}
- mutex_lock(&mgr->qlock);
txmsg->state = DRM_DP_SIDEBAND_TX_RX;
list_del(&txmsg->next);
+
mutex_unlock(&mgr->qlock);
wake_up_all(&mgr->tx_waitq);
--
2.44.2
