wifi: ath11k: cap out-of-range rx MCS instead of leaving bogus rate

Summary

In the Linux kernel, the following vulnerability has been resolved: wifi: ath11k: cap out-of-range rx MCS instead of leaving bogus rate ath11k can receive HT/VHT/HE frames whose reported MCS is above the maximum that can be expressed in the corresponding mac80211 rate space (e.g. an HE frame reported with MCS 12, while HE tops out at MCS 11). The frame itself is valid and decodes correctly, but for such a frame ath11k_dp_rx_h_rate() leaves rx_status->rate_idx set to the out-of-range value and never assigns rx_status->encoding, so it stays RX_ENC_LEGACY from the ath11k_dp_rx_h_ppdu() initialization. Once that frame reaches mac80211 it trips the rate sanity check and the frame is dropped with a splat: ath11k_pci 0000:03:00.0: Received with invalid mcs in HE mode 12 WARNING: CPU: 0 PID: 0 at net/mac80211/rx.c:5433 ieee80211_rx_list+0xb0a/0xe90 [mac80211] Dropping the frame would discard otherwise valid data, so instead cap the reported MCS to the maximum the rate space can express and deliver the frame. Set rx_status->encoding before the range check and assign rate_idx from the capped value, so a frame with an out-of-range MCS no longer leaves partial or bogus rate metadata behind. Also downgrade the logging level since they are not treated as invalid frames now. The only loss is that such a frame is reported as the capped MCS in the rx rate statistics. Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.41