brcmfmac: add length check in brcmf_cfg80211_escan_handler()

Upon handling the firmware notification for scans the length was
checked properly and may result in corrupting kernel heap memory
due to buffer overruns. This fix addresses CVE-2017-0786.

Cc: [email protected] # v4.0.x
Cc: Kevin Cernekee <[email protected]>
Reviewed-by: Hante Meuleman <[email protected]>
Reviewed-by: Pieter-Paul Giesberts <[email protected]>
Reviewed-by: Franky Lin <[email protected]>
Signed-off-by: Arend van Spriel <[email protected]>
Signed-off-by: Kalle Valo <[email protected]>

Author: Arend Van Spriel

drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c

@@ -3162,6 +3162,7 @@ brcmf_cfg80211_escan_handler(struct brcmf_if *ifp,
 	struct brcmf_cfg80211_info *cfg = ifp->drvr->config;
 	s32 status;
 	struct brcmf_escan_result_le *escan_result_le;
+	u32 escan_buflen;
 	struct brcmf_bss_info_le *bss_info_le;
 	struct brcmf_bss_info_le *bss = NULL;
 	u32 bi_length;
@@ -3181,11 +3182,23 @@ brcmf_cfg80211_escan_handler(struct brcmf_if *ifp,
 
 	if (status == BRCMF_E_STATUS_PARTIAL) {
 		brcmf_dbg(SCAN, "ESCAN Partial result\n");
+		if (e->datalen < sizeof(*escan_result_le)) {
+			brcmf_err("invalid event data length\n");
+			goto exit;
+		}
 		escan_result_le = (struct brcmf_escan_result_le *) data;
 		if (!escan_result_le) {
 			brcmf_err("Invalid escan result (NULL pointer)\n");
 			goto exit;
 		}
+		escan_buflen = le32_to_cpu(escan_result_le->buflen);
+		if (escan_buflen > BRCMF_ESCAN_BUF_SIZE ||
+		    escan_buflen > e->datalen ||
+		    escan_buflen < sizeof(*escan_result_le)) {
+			brcmf_err("Invalid escan buffer length: %d\n",
+				  escan_buflen);
+			goto exit;
+		}
 		if (le16_to_cpu(escan_result_le->bss_count) != 1) {
 			brcmf_err("Invalid bss_count %d: ignoring\n",
 				  escan_result_le->bss_count);
@@ -3202,9 +3215,8 @@ brcmf_cfg80211_escan_handler(struct brcmf_if *ifp,
 		}
 
 		bi_length = le32_to_cpu(bss_info_le->length);
-		if (bi_length != (le32_to_cpu(escan_result_le->buflen) -
-					WL_ESCAN_RESULTS_FIXED_SIZE)) {
-			brcmf_err("Invalid bss_info length %d: ignoring\n",
+		if (bi_length != escan_buflen -	WL_ESCAN_RESULTS_FIXED_SIZE) {
+			brcmf_err("Ignoring invalid bss_info length: %d\n",
 				  bi_length);
 			goto exit;
 		}