[PATCH] wifi: mac80211: warn on insufficient antennas for injected HT frames

[PATCH] wifi: mac80211: warn on insufficient antennas for injected HT frames

[WangYuli]

When injecting frames via radiotap, an HT MCS rate can be specified.
The number of chains for that MCS implies a minimum number of
antennas that must be enabled in the antenna bitmap. Previously,
if the antenna bitmap specified fewer antennas than required by the
MCS, the bitmap was silently cleared. This makes it hard to debug
issues with injected frames.

Add a WARN_ONCE() to log a descriptive error when this happens, make
it clear that the antenna configuration was insufficient and has
been reset.

Signed-off-by: WangYuli <wangyuli@uniontech.com>
---
 net/mac80211/tx.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index d58b80813bdd..e1464ef7397d 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2251,14 +2251,21 @@ bool ieee80211_parse_tx_radiotap(struct sk_buff *skb,
 		if (rate_flags & IEEE80211_TX_RC_MCS) {
 			/* reset antennas if not enough */
 			if (IEEE80211_HT_MCS_CHAINS(rate) >
-					hweight8(info->control.antennas))
+					hweight8(info->control.antennas)) {
+				WARN_ONCE(1, "Not enough antennas set for HT MCS chains (required: %d, set: %d), resetting antennas bitmap to 0\n",
+					  IEEE80211_HT_MCS_CHAINS(rate),
+					  hweight8(info->control.antennas));
 				info->control.antennas = 0;
+			}
 
 			info->control.rates[0].idx = rate;
 		} else if (rate_flags & IEEE80211_TX_RC_VHT_MCS) {
 			/* reset antennas if not enough */
-			if (vht_nss > hweight8(info->control.antennas))
+			if (vht_nss > hweight8(info->control.antennas)) {
+				WARN_ONCE(1, "Not enough antennas set for VHT MCS chains (required: %d, set: %d), resetting antennas bitmap to 0\n",
+					  vht_nss, hweight8(info->control.antennas));
 				info->control.antennas = 0;
+			}
 
 			ieee80211_rate_set_vht(info->control.rates, vht_mcs,
 					       vht_nss);
-- 
2.50.0

Re: [PATCH] wifi: mac80211: warn on insufficient antennas for injected HT frames

[Johannes Berg]

On Mon, 2025-07-14 at 17:44 +0800, WangYuli wrote:
> When injecting frames via radiotap, an HT MCS rate can be specified.
> The number of chains for that MCS implies a minimum number of
> antennas that must be enabled in the antenna bitmap. Previously,
> if the antenna bitmap specified fewer antennas than required by the
> MCS, the bitmap was silently cleared. This makes it hard to debug
> issues with injected frames.
> 
> Add a WARN_ONCE() to log a descriptive error when this happens, make
> it clear that the antenna configuration was insufficient and has
> been reset.
> 

No. We shouldn't WARN on userspace misbehaviour.

johannes