drm_dp_sideband_parse_remote_dpcd_read() reads num_bytes from the raw message and then unconditionally does:
memcpy(bytes, &raw->msg[idx], num_bytes); without checking that idx + num_bytes <= raw->curlen. raw->msg[] is 256 bytes; if a malicious or misbehaving MST hub sets num_bytes larger than the remaining payload, the memcpy reads past the received data into whatever follows in raw->msg[]. drm_dp_sideband_parse_remote_i2c_read_ack() has the same flaw (noted with a /* TODO check */ comment since the code was introduced). Fix both functions by using a single combined check (idx + num_bytes > curlen) before each memcpy. Since num_bytes is u8, it is always >= 0, so this strictly subsumes the simpler idx > curlen form and no separate step is needed. Cc: [email protected] Signed-off-by: Ashutosh Desai <[email protected]> --- Changes in v2: - Drop separate idx > curlen check; idx + num_bytes > curlen with u8 num_bytes (always >= 0) strictly subsumes it (Lyude Paul) drivers/gpu/drm/display/drm_dp_mst_topology.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index 170113520a43..9416a48804c8 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -871,7 +871,7 @@ static bool drm_dp_sideband_parse_remote_dpcd_read(struct drm_dp_sideband_msg_rx goto fail_len; repmsg->u.remote_dpcd_read_ack.num_bytes = raw->msg[idx]; idx++; - if (idx > raw->curlen) + if (idx + repmsg->u.remote_dpcd_read_ack.num_bytes > raw->curlen) goto fail_len; memcpy(repmsg->u.remote_dpcd_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_dpcd_read_ack.num_bytes); @@ -907,7 +907,9 @@ static bool drm_dp_sideband_parse_remote_i2c_read_ack(struct drm_dp_sideband_msg goto fail_len; repmsg->u.remote_i2c_read_ack.num_bytes = raw->msg[idx]; idx++; - /* TODO check */ + if (idx + repmsg->u.remote_i2c_read_ack.num_bytes > raw->curlen) + goto fail_len; + memcpy(repmsg->u.remote_i2c_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_i2c_read_ack.num_bytes); return true; fail_len: -- 2.34.1
