ALSA: line6: Fix write on zero-sized buffer

LINE6 drivers allocate the buffers based on the value returned from
usb_maxpacket() calls.  The manipulated device may return zero for
this, and this results in the kmalloc() with zero size (and it may
succeed) while the other part of the driver code writes the packet
data with the fixed size -- which eventually overwrites.

This patch adds a simple sanity check for the invalid buffer size for
avoiding that problem.

Reported-by: syzbot+219f00fb49874dcaea17@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/line6/pcm.c b/sound/usb/line6/pcm.c
index 72c6f8e82a7e9cb06e9c4489064d05dc39891448..78c2d6cab3b52f7341e7f02ee1e7e0d502f8679b 100644 (file)
--- a/sound/usb/line6/pcm.c
+++ b/sound/usb/line6/pcm.c
@@ -560,6 +560,11 @@ int line6_init_pcm(struct usb_line6 *line6,
        line6pcm->max_packet_size_out =
                usb_maxpacket(line6->usbdev,
                        usb_sndisocpipe(line6->usbdev, ep_write), 1);
+       if (!line6pcm->max_packet_size_in || !line6pcm->max_packet_size_out) {
+               dev_err(line6pcm->line6->ifcdev,
+                       "cannot get proper max packet size\n");
+               return -EINVAL;
+       }
 
        spin_lock_init(&line6pcm->out.lock);
        spin_lock_init(&line6pcm->in.lock);