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>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index d9a8c693457f..020387d76412 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -3168,6 +3168,23 @@ enum nl80211_commands {
  * @NL80211_ATTR_NPCA_PRIMARY_FREQ: NPCA primary channel (u32)
  * @NL80211_ATTR_NPCA_PUNCT_BITMAP: NPCA puncturing bitmap (u32)
  *
+ * @NL80211_ATTR_STA_DUMP_LINK_STATS: Request flag for %NL80211_CMD_GET_STATION
+ *	(dump mode only). When set on an MLD station, the dump produces two
+ *	%NL80211_CMD_NEW_STATION messages per station per dump call:
+ *
+ *	1. An aggregated-stats message whose top-level %NL80211_ATTR_STA_INFO
+ *	   contains MLO-combined statistics (same content as a dump without
+ *	   this flag).
+ *
+ *	2. For each active link, a per-link message containing
+ *	   %NL80211_ATTR_MLO_LINKS with a single link entry. Each entry holds
+ *	   %NL80211_ATTR_MLO_LINK_ID, the link-specific %NL80211_ATTR_MAC,
+ *	   and %NL80211_ATTR_STA_INFO with per-link statistics (see
+ *	   &enum nl80211_sta_info).
+ *
+ *	The aggregated message always precedes the per-link messages for the
+ *	same station within a dump sequence.
+ *
  * @NUM_NL80211_ATTR: total number of nl80211_attrs available
  * @NL80211_ATTR_MAX: highest attribute number currently defined
  * @__NL80211_ATTR_AFTER_LAST: internal use
@@ -3766,6 +3783,8 @@ enum nl80211_attrs {
 	NL80211_ATTR_NPCA_PRIMARY_FREQ,
 	NL80211_ATTR_NPCA_PUNCT_BITMAP,
 
+	NL80211_ATTR_STA_DUMP_LINK_STATS,
+
 	/* add attributes here, update the policy in nl80211.c */
 
 	__NL80211_ATTR_AFTER_LAST,