ALSA: usb-audio: us144mkii: Fix null-deref in tascam_midi_in_urb_complete()

The smatch tool reported a potential null pointer dereference in
tascam_midi_in_urb_complete(). The 'tascam' variable, derived from
'urb->context', was checked for nullity in one place, but dereferenced
without a check in several other places.

This patch fixes the issue by adding a null check at the beginning of
the function. If 'tascam' is null, the function now safely exits.
This prevents any potential crashes from null pointer dereferences.

It also fixes a latent bug where 'usb_put_urb()' could
be called twice for the same URB on submission failure, which would
lead to a use-after-free error.

Fixes: 67afec157fe6 ("ALSA: usb-audio: us144mkii: Add MIDI support and mixer controls")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202508192109.lcMrINK1-lkp@intel.com/
Signed-off-by: Šerif Rami <ramiserifpersia@gmail.com>
Link: https://patch.msgid.link/20250819185133.10464-1-ramiserifpersia@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/usx2y/us144mkii_midi.c b/sound/usb/usx2y/us144mkii_midi.c
index 5759f601007f815b388d1d540ad6ae2fe010814a..08b04aa392781c80e39e314501ef3bd137adfe7a 100644 (file)
--- a/sound/usb/usx2y/us144mkii_midi.c
+++ b/sound/usb/usx2y/us144mkii_midi.c
@@ -41,6 +41,9 @@ void tascam_midi_in_urb_complete(struct urb *urb)
        struct tascam_card *tascam = urb->context;
        int ret;
 
+       if (!tascam)
+               goto out;
+
        if (urb->status) {
                if (urb->status != -ENOENT && urb->status != -ECONNRESET &&
                    urb->status != -ESHUTDOWN && urb->status != -EPROTO) {
@@ -51,7 +54,7 @@ void tascam_midi_in_urb_complete(struct urb *urb)
                goto out;
        }
 
-       if (tascam && atomic_read(&tascam->midi_in_active) &&
+       if (atomic_read(&tascam->midi_in_active) &&
            urb->actual_length > 0) {
                kfifo_in_spinlocked(&tascam->midi_in_fifo, urb->transfer_buffer,
                                    urb->actual_length, &tascam->midi_in_lock);
@@ -65,8 +68,9 @@ void tascam_midi_in_urb_complete(struct urb *urb)
                dev_err(tascam->card->dev,
                        "Failed to resubmit MIDI IN URB: error %d\n", ret);
                usb_unanchor_urb(urb);
-               usb_put_urb(urb);
+               goto out;
        }
+
 out:
        usb_put_urb(urb);
 }