git.openwrt.org Git - openwrt/staging/rmilecki.git/blob

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: "Jason A. Donenfeld" <Jason@zx2c4.com>
   3 Date: Wed, 9 Sep 2020 13:58:14 +0200
   4 Subject: [PATCH] wireguard: noise: take lock when removing handshake entry
   5  from table
   6
   7 commit 9179ba31367bcf481c3c79b5f028c94faad9f30a upstream.
   8
   9 Eric reported that syzkaller found a race of this variety:
  10
  11 CPU 1                                       CPU 2
  12 -------------------------------------------|---------------------------------------
  13 wg_index_hashtable_replace(old, ...)       |
  14   if (hlist_unhashed(&old->index_hash))    |
  15                                            | wg_index_hashtable_remove(old)
  16                                            |   hlist_del_init_rcu(&old->index_hash)
  17                                            |     old->index_hash.pprev = NULL
  18   hlist_replace_rcu(&old->index_hash, ...) |
  19     *old->index_hash.pprev                 |
  20
  21 Syzbot wasn't actually able to reproduce this more than once or create a
  22 reproducer, because the race window between checking "hlist_unhashed" and
  23 calling "hlist_replace_rcu" is just so small. Adding an mdelay(5) or
  24 similar there helps make this demonstrable using this simple script:
  25
  26     #!/bin/bash
  27     set -ex
  28     trap 'kill $pid1; kill $pid2; ip link del wg0; ip link del wg1' EXIT
  29     ip link add wg0 type wireguard
  30     ip link add wg1 type wireguard
  31     wg set wg0 private-key <(wg genkey) listen-port 9999
  32     wg set wg1 private-key <(wg genkey) peer $(wg show wg0 public-key) endpoint 127.0.0.1:9999 persistent-keepalive 1
  33     wg set wg0 peer $(wg show wg1 public-key)
  34     ip link set wg0 up
  35     yes link set wg1 up | ip -force -batch - &
  36     pid1=$!
  37     yes link set wg1 down | ip -force -batch - &
  38     pid2=$!
  39     wait
  40
  41 The fundumental underlying problem is that we permit calls to wg_index_
  42 hashtable_remove(handshake.entry) without requiring the caller to take
  43 the handshake mutex that is intended to protect members of handshake
  44 during mutations. This is consistently the case with calls to wg_index_
  45 hashtable_insert(handshake.entry) and wg_index_hashtable_replace(
  46 handshake.entry), but it's missing from a pertinent callsite of wg_
  47 index_hashtable_remove(handshake.entry). So, this patch makes sure that
  48 mutex is taken.
  49
  50 The original code was a little bit funky though, in the form of:
  51
  52     remove(handshake.entry)
  53     lock(), memzero(handshake.some_members), unlock()
  54     remove(handshake.entry)
  55
  56 The original intention of that double removal pattern outside the lock
  57 appears to be some attempt to prevent insertions that might happen while
  58 locks are dropped during expensive crypto operations, but actually, all
  59 callers of wg_index_hashtable_insert(handshake.entry) take the write
  60 lock and then explicitly check handshake.state, as they should, which
  61 the aforementioned memzero clears, which means an insertion should
  62 already be impossible. And regardless, the original intention was
  63 necessarily racy, since it wasn't guaranteed that something else would
  64 run after the unlock() instead of after the remove(). So, from a
  65 soundness perspective, it seems positive to remove what looks like a
  66 hack at best.
  67
  68 The crash from both syzbot and from the script above is as follows:
  69
  70   general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
  71   KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  72   CPU: 0 PID: 7395 Comm: kworker/0:3 Not tainted 5.9.0-rc4-syzkaller #0
  73   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  74   Workqueue: wg-kex-wg1 wg_packet_handshake_receive_worker
  75   RIP: 0010:hlist_replace_rcu include/linux/rculist.h:505 [inline]
  76   RIP: 0010:wg_index_hashtable_replace+0x176/0x330 drivers/net/wireguard/peerlookup.c:174
  77   Code: 00 fc ff df 48 89 f9 48 c1 e9 03 80 3c 01 00 0f 85 44 01 00 00 48 b9 00 00 00 00 00 fc ff df 48 8b 45 10 48 89 c6 48 c1 ee 03 <80> 3c 0e 00 0f 85 06 01 00 00 48 85 d2 4c 89 28 74 47 e8 a3 4f b5
  78   RSP: 0018:ffffc90006a97bf8 EFLAGS: 00010246
  79   RAX: 0000000000000000 RBX: ffff888050ffc4f8 RCX: dffffc0000000000
  80   RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88808e04e010
  81   RBP: ffff88808e04e000 R08: 0000000000000001 R09: ffff8880543d0000
  82   R10: ffffed100a87a000 R11: 000000000000016e R12: ffff8880543d0000
  83   R13: ffff88808e04e008 R14: ffff888050ffc508 R15: ffff888050ffc500
  84   FS:  0000000000000000(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
  85   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  86   CR2: 00000000f5505db0 CR3: 0000000097cf7000 CR4: 00000000001526f0
  87   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  88   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  89   Call Trace:
  90   wg_noise_handshake_begin_session+0x752/0xc9a drivers/net/wireguard/noise.c:820
  91   wg_receive_handshake_packet drivers/net/wireguard/receive.c:183 [inline]
  92   wg_packet_handshake_receive_worker+0x33b/0x730 drivers/net/wireguard/receive.c:220
  93   process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
  94   worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
  95   kthread+0x3b5/0x4a0 kernel/kthread.c:292
  96   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
  97
  98 Reported-by: syzbot <syzkaller@googlegroups.com>
  99 Reported-by: Eric Dumazet <edumazet@google.com>
 100 Link: https://lore.kernel.org/wireguard/20200908145911.4090480-1-edumazet@google.com/
 101 Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
 102 Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
 103 Signed-off-by: David S. Miller <davem@davemloft.net>
 104 Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
 105 ---
 106  drivers/net/wireguard/noise.c | 5 +----
 107  1 file changed, 1 insertion(+), 4 deletions(-)
 108
 109 --- a/drivers/net/wireguard/noise.c
 110 +++ b/drivers/net/wireguard/noise.c
 111 @@ -87,15 +87,12 @@ static void handshake_zero(struct noise_
 112
 113  void wg_noise_handshake_clear(struct noise_handshake *handshake)
 114  {
 115 +       down_write(&handshake->lock);
 116         wg_index_hashtable_remove(
 117                         handshake->entry.peer->device->index_hashtable,
 118                         &handshake->entry);
 119 -       down_write(&handshake->lock);
 120         handshake_zero(handshake);
 121         up_write(&handshake->lock);
 122 -       wg_index_hashtable_remove(
 123 -                       handshake->entry.peer->device->index_hashtable,
 124 -                       &handshake->entry);
 125  }
 126
 127  static struct noise_keypair *keypair_create(struct wg_peer *peer)