[PATCH] ALSA: usb-audio: qcom: Check the return value of qmi_handle_init()

[Yuqiang Sun <izaiahsun@gmail.com>]

qc_usb_audio_probe() overwrites the return value of qmi_handle_init()
with that of qmi_add_server() without checking it. When
qmi_handle_init() fails, it has already freed the receive buffer and
destroyed the workqueue, and qmi->sock may hold an error pointer. If
QRTR is not available, qmi_handle_init() returns -EPROBE_DEFER and
qmi->sock is ERR_PTR(-EAFNOSUPPORT), so qmi_add_server() passes it to
kernel_sendmsg():

  BUG: unable to handle page fault for address: ffffffffffffffb7
  RIP: 0010:selinux_socket_sendmsg+0xa0/0x590
  Call Trace:
   security_socket_sendmsg+0x29/0x50
   __sock_sendmsg+0x43/0x150
   kernel_sendmsg+0xd6/0x180
   qmi_send_new_server+0x1b8/0x2b0
   qmi_add_server+0x165/0x200
   qc_usb_audio_probe+0xf4/0x2e0
   really_probe+0x2b4/0x850

Had the probe gone on, the error and remove paths would call
qmi_handle_release() on the half-initialized handle, which destroys the
workqueue and frees the receive buffer a second time.

Return the error from qmi_handle_init(), so that -EPROBE_DEFER defers
the probe, and check qmi_add_server() as well.

The bug was found with kbound, a static analysis prototype for
ownership mismatches at kernel interfaces, on v7.2.12; it is present in
mainline.

Build-tested with x86_64 and arm64 allmodconfig (W=1, sparse): no new
warnings. Run-tested on QEMU (x86_64, KVM) with KASAN and kmemleak, with
the driver built in and a test module that registers the
q6usb.qc-usb-audio-offload auxiliary device. Without QRTR, the probe
crashes as above without this patch; with it the device is deferred and
removing it again reports nothing. With QRTR the probe succeeds, and
removal reports nothing either.

Fixes: 326bbc348298 ("ALSA: usb-audio: qcom: Introduce QC USB SND offloading support")
Cc: stable@vger.kernel.org
Signed-off-by: Yuqiang Sun <izaiahsun@gmail.com>
---

Notes:
    The bug was found with kbound, a research static analysis prototype.
    The patch, the changelog and the test setup were written with the help
    of an AI coding assistant (Claude); I have reviewed and tested them as
    described above.
    
    The runs were on mainline d135ab453a74; the code this patch touches is
    the same there and in sound for-linus, which it is based on.

 sound/usb/qcom/qc_audio_offload.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
index e4bfd43a2488..5ee568e0454c 100644
--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -1969,8 +1969,13 @@ static int qc_usb_audio_probe(struct auxiliary_device *auxdev,
 			      QMI_UAUDIO_STREAM_REQ_MSG_V01_MAX_MSG_LEN,
 			      &uaudio_svc_ops_options,
 			      &uaudio_stream_req_handlers);
+	if (ret)
+		goto free_qmi_hdl;
+
 	ret = qmi_add_server(svc->uaudio_svc_hdl, UAUDIO_STREAM_SERVICE_ID_V01,
 			     UAUDIO_STREAM_SERVICE_VERS_V01, 0);
+	if (ret)
+		goto release_qmi_hdl;
 
 	uaudio_svc = svc;
 
@@ -1987,7 +1992,9 @@ static int qc_usb_audio_probe(struct auxiliary_device *auxdev,
 
 release_qmi:
 	qc_usb_audio_cleanup_qmi_dev();
+release_qmi_hdl:
 	qmi_handle_release(svc->uaudio_svc_hdl);
+free_qmi_hdl:
 	kfree(svc->uaudio_svc_hdl);
 free_svc:
 	kfree(svc);

base-commit: 56abaa599bbbee5500e166ddb0b5241a00c1f763
-- 
2.53.0