pending-4.9/alsa-seq-protect-in-kernel-ioctl-calls-with-mutex.patch

   1 From f803fd6dadeea3e9c512b50031a1ae253a19c46e Mon Sep 17 00:00:00 2001
   2 From: Takashi Iwai <tiwai@suse.de>
   3 Date: Tue, 9 Apr 2019 17:35:22 +0200
   4 Subject: ALSA: seq: Protect in-kernel ioctl calls with mutex
   5
   6 [ Upstream commit feb689025fbb6f0aa6297d3ddf97de945ea4ad32 ]
   7
   8 ALSA OSS sequencer calls the ioctl function indirectly via
   9 snd_seq_kernel_client_ctl().  While we already applied the protection
  10 against races between the normal ioctls and writes via the client's
  11 ioctl_mutex, this code path was left untouched.  And this seems to be
  12 the cause of still remaining some rare UAF as spontaneously triggered
  13 by syzkaller.
  14
  15 For the sake of robustness, wrap the ioctl_mutex also for the call via
  16 snd_seq_kernel_client_ctl(), too.
  17
  18 Reported-by: syzbot+e4c8abb920efa77bace9@syzkaller.appspotmail.com
  19 Signed-off-by: Takashi Iwai <tiwai@suse.de>
  20 Signed-off-by: Sasha Levin <sashal@kernel.org>
  21 ---
  22  sound/core/seq/seq_clientmgr.c | 9 +++++++--
  23  1 file changed, 7 insertions(+), 2 deletions(-)
  24
  25 diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
  26 index 09491b27092e..3b1b2e9fb33e 100644
  27 --- a/sound/core/seq/seq_clientmgr.c
  28 +++ b/sound/core/seq/seq_clientmgr.c
  29 @@ -2354,14 +2354,19 @@ int snd_seq_kernel_client_ctl(int clientid, unsigned int cmd, void *arg)
  30  {
  31         const struct ioctl_handler *handler;
  32         struct snd_seq_client *client;
  33 +       int err;
  34
  35         client = clientptr(clientid);
  36         if (client == NULL)
  37                 return -ENXIO;
  38
  39         for (handler = ioctl_handlers; handler->cmd > 0; ++handler) {
  40 -               if (handler->cmd == cmd)
  41 -                       return handler->func(client, arg);
  42 +               if (handler->cmd == cmd) {
  43 +                       mutex_lock(&client->ioctl_mutex);
  44 +                       err = handler->func(client, arg);
  45 +                       mutex_unlock(&client->ioctl_mutex);
  46 +                       return err;
  47 +               }
  48         }
  49
  50         pr_debug("ALSA: seq unknown ioctl() 0x%x (type='%c', number=0x%02x)\n",
  51 --
  52 2.20.1
  53