wifi: cfg80211: Fragment per-link station stats in nl80211_dump_station()

In MLO scenarios, stations may have multiple links, each with distinct
statistics. When userspace tools like iw or hostapd request station dumps,
attempting to pack all per-link stats into a single netlink message can
easily exceed the default 4KB buffer limit, especially when more than two
links are active. This results in -EMSGSIZE errors and incomplete data
delivery.

To address this, fragment per-link station statistics across multiple
netlink messages to ensure reliable delivery of complete MLO station
information. Extend the stateful context with a two-phase dump mechanism:
phase 0 (AGGREGATED) sends combined MLO-level statistics and phase 1
(PER_LINK) sends individual per-link statistics for each active link.

The dump loop is structured to produce exactly one netlink message per
iteration, with a common header (ifindex, wdev, mac, generation) built
once and phase-specific payload added via a switch statement. This keeps
header construction in one place and makes the EMSGSIZE bail-out uniform.

Add a new request flag attribute, NL80211_ATTR_STA_DUMP_LINK_STATS
(NLA_FLAG), for NL80211_CMD_GET_STATION dump. Userspace can set this
flag to request per-link station statistics for MLO stations.

Extract this flag during the first dump invocation by passing an attrbuf
to nl80211_prepare_wdev_dump(); use __free(kfree) to avoid scattered
manual kfree() calls. Cache the boolean in the dump context to avoid
repeated parsing on subsequent invocations.

Per-link messages carry a single NL80211_ATTR_MLO_LINKS nest with the
link ID, link-specific MAC, and per-link NL80211_ATTR_STA_INFO payload.
The link-specific validity (is_valid_ether_addr) and null pointer guard
are checked in nl80211_put_link_station_payload() before any message
construction begins.

Also fix all nla_nest_start_noflag() calls in nl80211_fill_link_station()
for nested attribute types (STA_INFO, BSS_PARAM, TID_STATS, per-tid) to
use nla_nest_start() so the NLA_F_NESTED flag is set correctly.

Propagate the actual return value from nl80211_put_sta_info_common() in
the AGGREGATED phase rather than returning skb->len. Returning skb->len
signals netlink to re-invoke the dump with the same sta_idx, causing an
infinite loop when the aggregated payload is too large to fit; returning
the real error code (-EMSGSIZE or otherwise) terminates the dump cleanly.

Backward compatibility is seamlessly preserved for non-MLO stations.

Signed-off-by: P Praneesh <praneesh.p@oss.qualcomm.com>
Link: https://patch.msgid.link/20260614051739.3979947-5-praneesh.p@oss.qualcomm.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

0 files changed, 0 insertions, 0 deletions