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151 lines
4.4 KiB
Diff
151 lines
4.4 KiB
Diff
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From: Johannes Berg <johannes.berg@intel.com>
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Date: Tue, 15 Nov 2016 12:05:11 +0100
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Subject: [PATCH] cfg80211: limit scan results cache size
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It's possible to make scanning consume almost arbitrary amounts
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of memory, e.g. by sending beacon frames with random BSSIDs at
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high rates while somebody is scanning.
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Limit the number of BSS table entries we're willing to cache to
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1000, limiting maximum memory usage to maybe 4-5MB, but lower
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in practice - that would be the case for having both full-sized
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beacon and probe response frames for each entry; this seems not
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possible in practice, so a limit of 1000 entries will likely be
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closer to 0.5 MB.
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Cc: stable@vger.kernel.org
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Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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---
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--- a/net/wireless/core.h
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+++ b/net/wireless/core.h
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@@ -71,6 +71,7 @@ struct cfg80211_registered_device {
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struct list_head bss_list;
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struct rb_root bss_tree;
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u32 bss_generation;
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+ u32 bss_entries;
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struct cfg80211_scan_request *scan_req; /* protected by RTNL */
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struct sk_buff *scan_msg;
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struct cfg80211_sched_scan_request __rcu *sched_scan_req;
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--- a/net/wireless/scan.c
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+++ b/net/wireless/scan.c
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@@ -57,6 +57,19 @@
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* also linked into the probe response struct.
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*/
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+/*
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+ * Limit the number of BSS entries stored in mac80211. Each one is
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+ * a bit over 4k at most, so this limits to roughly 4-5M of memory.
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+ * If somebody wants to really attack this though, they'd likely
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+ * use small beacons, and only one type of frame, limiting each of
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+ * the entries to a much smaller size (in order to generate more
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+ * entries in total, so overhead is bigger.)
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+ */
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+static int bss_entries_limit = 1000;
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+module_param(bss_entries_limit, int, 0644);
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+MODULE_PARM_DESC(bss_entries_limit,
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+ "limit to number of scan BSS entries (per wiphy, default 1000)");
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+
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#define IEEE80211_SCAN_RESULT_EXPIRE (30 * HZ)
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static void bss_free(struct cfg80211_internal_bss *bss)
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@@ -137,6 +150,10 @@ static bool __cfg80211_unlink_bss(struct
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list_del_init(&bss->list);
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rb_erase(&bss->rbn, &rdev->bss_tree);
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+ rdev->bss_entries--;
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+ WARN_ONCE((rdev->bss_entries == 0) ^ list_empty(&rdev->bss_list),
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+ "rdev bss entries[%d]/list[empty:%d] corruption\n",
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+ rdev->bss_entries, list_empty(&rdev->bss_list));
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bss_ref_put(rdev, bss);
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return true;
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}
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@@ -163,6 +180,40 @@ static void __cfg80211_bss_expire(struct
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rdev->bss_generation++;
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}
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+static bool cfg80211_bss_expire_oldest(struct cfg80211_registered_device *rdev)
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+{
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+ struct cfg80211_internal_bss *bss, *oldest = NULL;
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+ bool ret;
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+
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+ lockdep_assert_held(&rdev->bss_lock);
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+
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+ list_for_each_entry(bss, &rdev->bss_list, list) {
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+ if (atomic_read(&bss->hold))
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+ continue;
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+
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+ if (!list_empty(&bss->hidden_list) &&
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+ !bss->pub.hidden_beacon_bss)
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+ continue;
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+
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+ if (oldest && time_before(oldest->ts, bss->ts))
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+ continue;
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+ oldest = bss;
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+ }
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+
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+ if (WARN_ON(!oldest))
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+ return false;
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+
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+ /*
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+ * The callers make sure to increase rdev->bss_generation if anything
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+ * gets removed (and a new entry added), so there's no need to also do
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+ * it here.
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+ */
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+
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+ ret = __cfg80211_unlink_bss(rdev, oldest);
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+ WARN_ON(!ret);
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+ return ret;
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+}
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+
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void ___cfg80211_scan_done(struct cfg80211_registered_device *rdev,
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bool send_message)
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{
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@@ -689,6 +740,7 @@ static bool cfg80211_combine_bsses(struc
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const u8 *ie;
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int i, ssidlen;
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u8 fold = 0;
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+ u32 n_entries = 0;
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ies = rcu_access_pointer(new->pub.beacon_ies);
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if (WARN_ON(!ies))
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@@ -712,6 +764,12 @@ static bool cfg80211_combine_bsses(struc
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/* This is the bad part ... */
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list_for_each_entry(bss, &rdev->bss_list, list) {
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+ /*
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+ * we're iterating all the entries anyway, so take the
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+ * opportunity to validate the list length accounting
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+ */
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+ n_entries++;
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+
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if (!ether_addr_equal(bss->pub.bssid, new->pub.bssid))
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continue;
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if (bss->pub.channel != new->pub.channel)
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@@ -740,6 +798,10 @@ static bool cfg80211_combine_bsses(struc
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new->pub.beacon_ies);
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}
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+ WARN_ONCE(n_entries != rdev->bss_entries,
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+ "rdev bss entries[%d]/list[len:%d] corruption\n",
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+ rdev->bss_entries, n_entries);
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+
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return true;
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}
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@@ -894,7 +956,14 @@ cfg80211_bss_update(struct cfg80211_regi
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}
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}
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+ if (rdev->bss_entries >= bss_entries_limit &&
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+ !cfg80211_bss_expire_oldest(rdev)) {
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+ kfree(new);
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+ goto drop;
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+ }
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+
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list_add_tail(&new->list, &rdev->bss_list);
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+ rdev->bss_entries++;
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rb_insert_bss(rdev, new);
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found = new;
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}
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