Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider: - [High] drm/dp_mst: Data race and logical flaw in allocated_pbn causes spurious -ENOSPC - [High] drm/dp_mst: Unvalidated allocated_pbn from device causes permanent DoS --
commit 4a7c9a56c428ab20bf4027cd5c4e8a720688111a Author: Xiao Lu <[email protected]> drm/dp_mst: Track allocated_pbn from ALLOCATE_PAYLOAD down-reply This commit stores the allocated_pbn returned by the ALLOCATE_PAYLOAD down-reply sideband message. It uses the larger of requested PBN and allocated PBN for the MST bandwidth limit checks, carrying the value across dependent atomic commits. > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c > b/drivers/gpu/drm/display/drm_dp_mst_topology.c > index 7ce9e212770ad..b0e4cf8458eda 100644 > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c > @@ -3166,10 +3167,14 @@ static int drm_dp_payload_send_msg(struct > drm_dp_mst_topology_mgr *mgr, > */ > ret = drm_dp_mst_wait_tx_reply(mstb, txmsg); > if (ret > 0) { > - if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) > + if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) { > ret = -EINVAL; > - else > + } else { > + if (payload) > + payload->allocated_pbn = > + > txmsg->reply.u.allocate_payload.allocated_pbn; [Severity: High] Is it safe to write to the active atomic state payload from an asynchronous worker here without modeset locks? If drm_dp_add_payload_part2() locklessly mutates allocated_pbn concurrently with drm_dp_mst_duplicate_state(), could this result in a data race? [Severity: High] Is this untrusted 16-bit value from the branch device saved into the payload state here without bounds checking? If a malicious or malfunctioning branch device replies to the ALLOCATE_PAYLOAD message with a spoofed allocated_pbn value (e.g., 65535), could it be stored directly without validation? > ret = 0; > + } > } > kfree(txmsg); > fail_put: [ ... ] > @@ -4670,6 +4678,7 @@ void drm_dp_mst_atomic_wait_for_dependencies(struct > drm_atomic_commit *state) > new_payload = > drm_atomic_get_mst_payload_state(new_mst_state, > > old_payload->port); > new_payload->vc_start_slot = old_payload->vc_start_slot; > + new_payload->allocated_pbn = old_payload->allocated_pbn; [Severity: High] Could this unconditional restore overwrite the 0 set by drm_dp_atomic_find_time_slots() during the atomic check phase? If it does, could it inflate the perceived bandwidth for concurrent checks? > new_payload->payload_allocation_status = > > old_payload->payload_allocation_status; > } [ ... ] > @@ -5352,7 +5361,7 @@ drm_dp_mst_atomic_check_port_bw_limit(struct > drm_dp_mst_port *port, > return -EINVAL; > } > > - pbn_used = payload->pbn; > + pbn_used = max(payload->pbn, payload->allocated_pbn); [Severity: High] Does evaluating this max() with a potentially stale or artificially inflated value concurrently produce incorrect bandwidth checks? If so, could it cause spurious -ENOSPC failures in bandwidth validation, causing display configurations to fail randomly? Also, if a maliciously huge value was evaluated here, could it force pbn_used > port->full_pbn, failing the check? Since the topology check iterates over all payloads, could this permanently prevent any future display configurations on this topology? > } else { > pbn_used = drm_dp_mst_atomic_check_mstb_bw_limit(port->mstb, -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=2
