wifi: mac80211: bounds-check link_id in ieee80211_ml_epcs

wifi: mac80211: bounds-check link_id in ieee80211_ml_epcs

IEEE80211_MLE_STA_EPCS_CONTROL_LINK_ID is 0x000f, so link_id extracted
from a PRIO_ACCESS ML element PER_STA_PROFILE subelement can be 0..15.
sdata->link[] has IEEE80211_MLD_MAX_NUM_LINKS (15) entries (indices 0..14),
making index 15 out-of-bounds.

A connected WiFi 7 AP can trigger this by sending an EPCS Enable Response
action frame with a PER_STA_PROFILE subelement where link_id = 15.  The
unsolicited-notification path (dialog_token = 0) is reachable any time
EPCS is already enabled, without any prior client request.

sdata->link[15] reads into the first word of sdata->activate_links_work
(a wiphy_work whose embedded list_head is non-NULL after INIT_LIST_HEAD),
so the NULL check on the result does not catch the invalid access.  The
garbage pointer is then passed to ieee80211_sta_wmm_params(), which
dereferences link->sdata and crashes the kernel.

The same class of bug was fixed for ieee80211_ml_reconfiguration() by
commit 162d331d833d ("wifi: mac80211: bounds-check link_id in
ieee80211_ml_reconfiguration").

Fixes: de86c5f60839 ("wifi: mac80211: Add support for EPCS configuration")
Signed-off-by: Alexandru Hossu <hossu.alexandru@gmail.com>
Link: https://patch.msgid.link/20260515102908.1653088-1-hossu.alexandru@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>