wifi: cfg80211: validate IEs in cfg80211_wext_siwgenie()

In the Linux kernel, the following vulnerability has been resolved: wifi: cfg80211: validate IEs in cfg80211_wext_siwgenie() The KASAN allocation trace shows that a malformed IE buffer is stored via SIOCSIWGENIE (cfg80211_wext_siwgenie()) without any validation. The crash trace shows that a subsequent SIOCSIWESSID triggers a connection attempt which calls cfg80211_sme_get_conn_ies() to process the stored IE buffer, causing: - An out-of-bounds read in skip_ie() which reads ies[pos+1] (the length byte) past the end of the 1-byte buffer. - An integer underflow in the memcpy size argument when offs returned by ieee80211_ie_split() exceeds ies_len, causing unsigned subtraction to wrap to SIZE_MAX and triggering a fortify panic. Fix this by validating the IE buffer in cfg80211_wext_siwgenie() before storing it. [drop unnecessary ie_len check, update commit message]