[PATCH v3 2/2] wifi: nl80211: re-check wiphy netns in nl80211_prepare_wdev_dump() continuation

[Maoyi Xie <maoyixie.tju@gmail.com>]

From: Maoyi Xie <maoyi.xie@ntu.edu.sg>

NL80211_CMD_GET_SCAN is implemented as a multi-call dumpit. The first
invocation of nl80211_prepare_wdev_dump() validates the requested wdev
against the caller's netns via __cfg80211_wdev_from_attrs(). Subsequent
invocations look up the same wiphy by global index via
wiphy_idx_to_wiphy() and do not re-check that the wiphy is still in
the caller's netns.

If the wiphy is moved between dumpit invocations (via
NL80211_CMD_SET_WIPHY_NETNS), the dump silently continues to copy BSS
list contents from the wiphy's new netns into the caller's netns
socket buffer. The other dump paths in nl80211.c (e.g.
nl80211_dump_wiphy() and the parallel scheduled scan dump) already
filter by net_eq(wiphy_net(...), sock_net(skb->sk)) on every iteration.

Add the same filter to the continuation path. If the wiphy's netns no
longer matches the caller's, return -ENODEV and the netlink dump
machinery terminates the walk cleanly.

This is most usefully fixed alongside the SET_WIPHY_NETNS target-cap
hardening in patch 1/2, which closes the path by which an
unprivileged-userns caller could trigger this race themselves.

Signed-off-by: Maoyi Xie <maoyi.xie@ntu.edu.sg>
---
 net/wireless/nl80211.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index db546dd93..f2c91a939 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -1276,6 +1276,16 @@ static int nl80211_prepare_wdev_dump(struct netlink_callback *cb,
 			rtnl_unlock();
 			return -ENODEV;
 		}
+		/*
+		 * The first invocation validated the wdev's netns against
+		 * the caller via __cfg80211_wdev_from_attrs(). The wiphy
+		 * may have moved netns between dumpit invocations (via
+		 * NL80211_CMD_SET_WIPHY_NETNS), so re-check here.
+		 */
+		if (!net_eq(wiphy_net(wiphy), sock_net(cb->skb->sk))) {
+			rtnl_unlock();
+			return -ENODEV;
+		}
 		*rdev = wiphy_to_rdev(wiphy);
 		*wdev = NULL;
 
-- 
2.34.1