wifi: cfg80211: advance loop vars in cfg80211_merge_profile()

cfg80211_merge_profile() reassembles a Multi-BSSID non-transmitted BSS profile that has been split across multiple consecutive MBSSID elements. Its while-loop calls

cfg80211_get_profile_continuation(ie, ielen, mbssid_elem, sub_elem)

but never advances mbssid_elem or sub_elem inside the body. Each iteration therefore searches for a continuation that follows the same fixed pair; the helper returns the same next_mbssid; and the same next_sub bytes are memcpy()'d into merged_ie at a growing offset until the buffer fills.

Advance both mbssid_elem and sub_elem to the just-consumed continuation so the next call to cfg80211_get_profile_continuation() searches for a further continuation beyond it (or returns NULL when none exists).

A specially-crafted malicious beacon can take advantage of this bug to cause the kernel to spend an excessive amount of time in cfg80211_merge_profile (up to as much as 2ms per beacon recieved), which could theoretically be abused in some way.

---
 net/wireless/scan.c | 3 +++
 1 file changed, 3 insertions(+)

index 328af43ef832..358cbc9e43d8 100644
@@ -2462,6 +2462,9 @@ size_t cfg80211_merge_profile(const u8 *ie, size_t ielen,
 		memcpy(merged_ie + copied_len, next_sub->data,
 		       next_sub->datalen);
 		copied_len += next_sub->datalen;
+
+		mbssid_elem = next_mbssid;
+		sub_elem = next_sub;
 	}
 
 	return copied_len;

base-commit: fcee7d82f27d6a8b1ddc5bbefda59b4e441e9bc0

2.50.1 (Apple Git-155)