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drm/dp_mst: Fix down request message timeout handling

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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@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241203174632.2941402-1-imre.deak@intel.com
This commit is contained in:
Imre Deak 2024-12-03 19:46:32 +02:00
parent b559b68d27
commit 3f61185503
1 changed files with 9 additions and 3 deletions
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12
drivers/gpu/drm/display/drm_dp_mst_topology.c
View File

@ -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);