wifi: mac80211: consume only present negotiated TTLM maps

ieee80211_tid_to_link_map_size_ok() validates negotiated TTLM elements
against the number of link-map entries indicated by link_map_presence.
ieee80211_parse_neg_ttlm() must consume the same layout.

The parser advanced its cursor for every TID, including TIDs whose
presence bit is clear and therefore have no map bytes in the element.
A sparse map can then make a later present TID read past the validated
element.

The bad bytes land in neg_ttlm->{up,down}link[tid] but are gated by
valid_links before being applied to driver state, so a peer cannot
turn the read into a policy change.  Under KUnit + KASAN with an
exact-sized element allocation the OOB read is reported as a
slab-out-of-bounds; whether the same trigger fires under the
production RX path depends on surrounding allocator state.

Advance the cursor only when the current TID has a map present.

Fixes: 8f500fb ("wifi: mac80211: process and save negotiated TID to Link mapping request")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://patch.msgid.link/20260515151719.1317659-2-michael.bommarito@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: mjbommar

net/mac80211/mlme.c

@@ -8164,6 +8164,7 @@ ieee80211_parse_neg_ttlm(struct ieee80211_sub_if_data *sdata,
 					 "No active links for TID %d", tid);
 				return -EINVAL;
 			}
+			pos += map_size;
 		} else {
 			map = 0;
 		}
@@ -8182,7 +8183,6 @@ ieee80211_parse_neg_ttlm(struct ieee80211_sub_if_data *sdata,
 		default:
 			return -EINVAL;
 		}
-		pos += map_size;
 	}
 	return 0;
 }