target/linux/generic/backport-5.4/080-wireguard-0115-wireguard-peerlookup-take-lock-before-checking-hash-.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: "Jason A. Donenfeld" <Jason@zx2c4.com>
   3 Date: Wed, 9 Sep 2020 13:58:15 +0200
   4 Subject: [PATCH] wireguard: peerlookup: take lock before checking hash in
   5  replace operation
   6
   7 commit 6147f7b1e90ff09bd52afc8b9206a7fcd133daf7 upstream.
   8
   9 Eric's suggested fix for the previous commit's mentioned race condition
  10 was to simply take the table->lock in wg_index_hashtable_replace(). The
  11 table->lock of the hash table is supposed to protect the bucket heads,
  12 not the entires, but actually, since all the mutator functions are
  13 already taking it, it makes sense to take it too for the test to
  14 hlist_unhashed, as a defense in depth measure, so that it no longer
  15 races with deletions, regardless of what other locks are protecting
  16 individual entries. This is sensible from a performance perspective
  17 because, as Eric pointed out, the case of being unhashed is already the
  18 unlikely case, so this won't add common contention. And comparing
  19 instructions, this basically doesn't make much of a difference other
  20 than pushing and popping %r13, used by the new `bool ret`. More
  21 generally, I like the idea of locking consistency across table mutator
  22 functions, and this might let me rest slightly easier at night.
  23
  24 Suggested-by: Eric Dumazet <edumazet@google.com>
  25 Link: https://lore.kernel.org/wireguard/20200908145911.4090480-1-edumazet@google.com/
  26 Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
  27 Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
  28 Signed-off-by: David S. Miller <davem@davemloft.net>
  29 Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
  30 ---
  31  drivers/net/wireguard/peerlookup.c | 11 ++++++++---
  32  1 file changed, 8 insertions(+), 3 deletions(-)
  33
  34 --- a/drivers/net/wireguard/peerlookup.c
  35 +++ b/drivers/net/wireguard/peerlookup.c
  36 @@ -167,9 +167,13 @@ bool wg_index_hashtable_replace(struct i
  37                                 struct index_hashtable_entry *old,
  38                                 struct index_hashtable_entry *new)
  39  {
  40 -       if (unlikely(hlist_unhashed(&old->index_hash)))
  41 -               return false;
  42 +       bool ret;
  43 +
  44         spin_lock_bh(&table->lock);
  45 +       ret = !hlist_unhashed(&old->index_hash);
  46 +       if (unlikely(!ret))
  47 +               goto out;
  48 +
  49         new->index = old->index;
  50         hlist_replace_rcu(&old->index_hash, &new->index_hash);
  51
  52 @@ -180,8 +184,9 @@ bool wg_index_hashtable_replace(struct i
  53          * simply gets dropped, which isn't terrible.
  54          */
  55         INIT_HLIST_NODE(&old->index_hash);
  56 +out:
  57         spin_unlock_bh(&table->lock);
  58 -       return true;
  59 +       return ret;
  60  }
  61
  62  void wg_index_hashtable_remove(struct index_hashtable *table,