queue-5.0/batman-adv-reduce-tt_global-hash-refcnt-only-for-rem.patch

   1 From beb2793bde0067d9a12b29cab7323c9cc906f4e2 Mon Sep 17 00:00:00 2001
   2 From: Sven Eckelmann <sven@narfation.org>
   3 Date: Sat, 23 Feb 2019 14:27:10 +0100
   4 Subject: batman-adv: Reduce tt_global hash refcnt only for removed entry
   5
   6 [ Upstream commit f131a56880d10932931e74773fb8702894a94a75 ]
   7
   8 The batadv_hash_remove is a function which searches the hashtable for an
   9 entry using a needle, a hashtable bucket selection function and a compare
  10 function. It will lock the bucket list and delete an entry when the compare
  11 function matches it with the needle. It returns the pointer to the
  12 hlist_node which matches or NULL when no entry matches the needle.
  13
  14 The batadv_tt_global_free is not itself protected in anyway to avoid that
  15 any other function is modifying the hashtable between the search for the
  16 entry and the call to batadv_hash_remove. It can therefore happen that the
  17 entry either doesn't exist anymore or an entry was deleted which is not the
  18 same object as the needle. In such an situation, the reference counter (for
  19 the reference stored in the hashtable) must not be reduced for the needle.
  20 Instead the reference counter of the actually removed entry has to be
  21 reduced.
  22
  23 Otherwise the reference counter will underflow and the object might be
  24 freed before all its references were dropped. The kref helpers reported
  25 this problem as:
  26
  27   refcount_t: underflow; use-after-free.
  28
  29 Fixes: 7683fdc1e886 ("batman-adv: protect the local and the global trans-tables with rcu")
  30 Reported-by: Martin Weinelt <martin@linuxlounge.net>
  31 Signed-off-by: Sven Eckelmann <sven@narfation.org>
  32 Acked-by: Antonio Quartulli <a@unstable.cc>
  33 Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
  34 Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
  35 ---
  36  net/batman-adv/translation-table.c | 18 +++++++++++++++---
  37  1 file changed, 15 insertions(+), 3 deletions(-)
  38
  39 diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
  40 index 2ee87d3ca6d0..6ec0e67be560 100644
  41 --- a/net/batman-adv/translation-table.c
  42 +++ b/net/batman-adv/translation-table.c
  43 @@ -616,14 +616,26 @@ static void batadv_tt_global_free(struct batadv_priv *bat_priv,
  44                                   struct batadv_tt_global_entry *tt_global,
  45                                   const char *message)
  46  {
  47 +       struct batadv_tt_global_entry *tt_removed_entry;
  48 +       struct hlist_node *tt_removed_node;
  49 +
  50         batadv_dbg(BATADV_DBG_TT, bat_priv,
  51                    "Deleting global tt entry %pM (vid: %d): %s\n",
  52                    tt_global->common.addr,
  53                    batadv_print_vid(tt_global->common.vid), message);
  54
  55 -       batadv_hash_remove(bat_priv->tt.global_hash, batadv_compare_tt,
  56 -                          batadv_choose_tt, &tt_global->common);
  57 -       batadv_tt_global_entry_put(tt_global);
  58 +       tt_removed_node = batadv_hash_remove(bat_priv->tt.global_hash,
  59 +                                            batadv_compare_tt,
  60 +                                            batadv_choose_tt,
  61 +                                            &tt_global->common);
  62 +       if (!tt_removed_node)
  63 +               return;
  64 +
  65 +       /* drop reference of remove hash entry */
  66 +       tt_removed_entry = hlist_entry(tt_removed_node,
  67 +                                      struct batadv_tt_global_entry,
  68 +                                      common.hash_entry);
  69 +       batadv_tt_global_entry_put(tt_removed_entry);
  70  }
  71
  72  /**
  73 --
  74 2.20.1
  75