rsi_prepare_beacon() copies the mac80211 beacon frame after
FRAME_DESC_SZ into a management skb whose usable tailroom may be smaller
than MAX_MGMT_PKT_SIZE after alignment.

Validate the beacon length against the actual tailroom before the copy
and skb_put(). Leave ownership of the management skb with the caller on
error, matching the existing rsi_send_beacon() cleanup path.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
diff --git a/drivers/net/wireless/rsi/rsi_91x_hal.c b/drivers/net/wireless/rsi/rsi_91x_hal.c
--- a/drivers/net/wireless/rsi/rsi_91x_hal.c
+++ b/drivers/net/wireless/rsi/rsi_91x_hal.c
@@ -431,6 +431,7 @@
 	struct ieee80211_vif *vif;
 	struct sk_buff *mac_bcn;
 	u8 vap_id = 0, i;
+	unsigned int tailroom;
 	u16 tim_offset = 0;
 
 	for (i = 0; i < RSI_MAX_VIFS; i++) {
@@ -479,6 +480,13 @@
 
 	if (mac_bcn->data[tim_offset + 2] == 0)
 		bcn_frm->frame_info |= cpu_to_le16(RSI_DATA_DESC_DTIM_BEACON);
+
+	tailroom = skb_tailroom(skb);
+	if (tailroom < FRAME_DESC_SZ ||
+	    mac_bcn->len > tailroom - FRAME_DESC_SZ) {
+		dev_kfree_skb(mac_bcn);
+		return -EMSGSIZE;
+	}
 
 	memcpy(&skb->data[FRAME_DESC_SZ], mac_bcn->data, mac_bcn->len);
 	skb_put(skb, mac_bcn->len + FRAME_DESC_SZ);