reject oversized EMA RNR lists

Summary

In the Linux kernel, the following vulnerability has been resolved: wifi: nl80211: reject oversized EMA RNR lists nl80211_parse_rnr_elems() stores the parsed element count in a u8-backed cfg80211_rnr_elems::cnt field and uses that count to size the flexible array allocation. Reject nested NL80211_ATTR_EMA_RNR_ELEMS input once the count reaches 255, before incrementing it again. This keeps the parser aligned with the data structure it fills and matches the existing bound check used by nl80211_parse_mbssid_elems(). The nl80211_parse_rnr_elems() function, responsible for parsing EMA RNR (Enhanced Multiple Access Reduced Neighbor Report) lists, does not properly handle an excessive number of nested NL80211_ATTR_EMA_RNR_ELEMS inputs. This improper input validation could allow a remote attacker to cause a denial of service (DoS) by providing an oversized EMA RNR list, potentially leading to system instability or a crash. Red Hat severity: Moderate — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H). Weakness: CWE-770. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9. Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat does not currently list a fixing RHSA for this CVE.