[PATCH v2] wireless: mt76: mt7921: Fix use-after-free in fw features query.

[greearb@candelatech.com]

From: Ben Greear <greearb@candelatech.com>

Stop referencing 'features' memory after release_firmware is called.

Fixes this crash:

RIP: 0010:mt7921_check_offload_capability+0x17d
mt7921_pci_probe+0xca/0x4b0
...

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
 drivers/net/wireless/mediatek/mt76/mt7921/init.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/init.c b/drivers/net/wireless/mediatek/mt76/mt7921/init.c
index 38d6563cb12f..d2bb8d02ce0a 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7921/init.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7921/init.c
@@ -165,12 +165,12 @@ mt7921_mac_init_band(struct mt7921_dev *dev, u8 band)
 
 u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
 {
-	struct mt7921_fw_features *features = NULL;
 	const struct mt76_connac2_fw_trailer *hdr;
 	struct mt7921_realease_info *rel_info;
 	const struct firmware *fw;
 	int ret, i, offset = 0;
 	const u8 *data, *end;
+	u8 offload_caps = 0;
 
 	ret = request_firmware(&fw, fw_wm, dev);
 	if (ret)
@@ -197,12 +197,19 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
 	data += sizeof(*rel_info);
 	end = data + le16_to_cpu(rel_info->len);
 
+	/* TODO:  This needs better sanity checking I think.
+	 * Likely a corrupted firmware with bad rel_info->len, for instance,
+	 * would blow this up.
+	 */
 	while (data < end) {
 		rel_info = (struct mt7921_realease_info *)data;
 		data += sizeof(*rel_info);
 
 		if (rel_info->tag == MT7921_FW_TAG_FEATURE) {
+			struct mt7921_fw_features *features;
+
 			features = (struct mt7921_fw_features *)data;
+			offload_caps = features->data;
 			break;
 		}
 
@@ -211,7 +218,7 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
 
 	release_firmware(fw);
 
-	return features ? features->data : 0;
+	return offload_caps;
 }
 EXPORT_SYMBOL_GPL(mt7921_check_offload_capability);
 
-- 
2.39.1