ALSA: seq: Fix missing NULL check at remove_events ioctl

commit 030e2c78d3a91dd0d27fef37e91950dde333eba1 upstream.

snd_seq_ioctl_remove_events() calls snd_seq_fifo_clear()
unconditionally even if there is no FIFO assigned, and this leads to
an Oops due to NULL dereference.  The fix is just to add a proper NULL
check.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: Mark Salyzyn <salyzyn@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 41347ad1c4d53c3782f437139e60f034ff3bb0e9..a3988a4bcfd6653118a951daaae8fdb99bfcdf9e 100644 (file)
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1970,7 +1970,7 @@ static int snd_seq_ioctl_remove_events(struct snd_seq_client *client,
                 * No restrictions so for a user client we can clear
                 * the whole fifo
                 */
-               if (client->type == USER_CLIENT)
+               if (client->type == USER_CLIENT && client->data.user.fifo)
                        snd_seq_fifo_clear(client->data.user.fifo);
        }