ALSA: seq: Fix potential concurrent access to the deleted pool

commit 75545304eba6a3d282f923b96a466dc25a81e359 upstream.

The input pool of a client might be deleted via the resize ioctl, the
the access to it should be covered by the proper locks.  Currently the
only missing place is the call in snd_seq_ioctl_get_client_pool(), and
this patch papers over it.

Reported-by: syzbot+4a75454b9ca2777f35c7@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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 7fa0219..331a2b0 100644 (file)
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1906,8 +1906,7 @@ static int snd_seq_ioctl_get_client_pool(struct snd_seq_client *client,
        if (cptr->type == USER_CLIENT) {
                info.input_pool = cptr->data.user.fifo_pool_size;
                info.input_free = info.input_pool;
-               if (cptr->data.user.fifo)
-                       info.input_free = snd_seq_unused_cells(cptr->data.user.fifo->pool);
+               info.input_free = snd_seq_fifo_unused_cells(cptr->data.user.fifo);
        } else {
                info.input_pool = 0;
                info.input_free = 0;

diff --git a/sound/core/seq/seq_fifo.c b/sound/core/seq/seq_fifo.c
index 9acbed1..d9f5428 100644 (file)
--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -278,3 +278,20 @@ int snd_seq_fifo_resize(struct snd_seq_fifo *f, int poolsize)
 
        return 0;
 }
+
+/* get the number of unused cells safely */
+int snd_seq_fifo_unused_cells(struct snd_seq_fifo *f)
+{
+       unsigned long flags;
+       int cells;
+
+       if (!f)
+               return 0;
+
+       snd_use_lock_use(&f->use_lock);
+       spin_lock_irqsave(&f->lock, flags);
+       cells = snd_seq_unused_cells(f->pool);
+       spin_unlock_irqrestore(&f->lock, flags);
+       snd_use_lock_free(&f->use_lock);
+       return cells;
+}

diff --git a/sound/core/seq/seq_fifo.h b/sound/core/seq/seq_fifo.h
index 062c446..5d38a0d 100644 (file)
--- a/sound/core/seq/seq_fifo.h
+++ b/sound/core/seq/seq_fifo.h
@@ -68,5 +68,7 @@ int snd_seq_fifo_poll_wait(struct snd_seq_fifo *f, struct file *file, poll_table
 /* resize pool in fifo */
 int snd_seq_fifo_resize(struct snd_seq_fifo *f, int poolsize);
 
+/* get the number of unused cells safely */
+int snd_seq_fifo_unused_cells(struct snd_seq_fifo *f);
 
 #endif