Re: [PATCH] ALSA: usb-audio: Fix a DMA to stack memory bug

[Benoît Sevens <bsevens@xxxxxxxxxx>]

Hi Dan,

On Mon, 2 Dec 2024 at 13:57, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> The usb_get_descriptor() function does DMA so we're not allowed
> to use a stack buffer for that.  Doing DMA to the stack is not portable
> all architectures.  Move the "new_device_descriptor" from being stored
> on the stack and allocate it with kmalloc() instead.
>

Thanks for fixing this. It looks good to me.

Note that the commit that is being fixed is already queued for
backporting, so I don't know how this usually goes then.

> Fixes: b909df18ce2a ("ALSA: usb-audio: Fix potential out-of-bound accesses for Extigy and Mbox devices")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
>  sound/usb/quirks.c | 42 +++++++++++++++++++++++++++---------------
>  1 file changed, 27 insertions(+), 15 deletions(-)
>
> diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
> index 8bc959b60be3..7c9d352864da 100644
> --- a/sound/usb/quirks.c
> +++ b/sound/usb/quirks.c
> @@ -555,7 +555,7 @@ int snd_usb_create_quirk(struct snd_usb_audio *chip,
>  static int snd_usb_extigy_boot_quirk(struct usb_device *dev, struct usb_interface *intf)
>  {
>         struct usb_host_config *config = dev->actconfig;
> -       struct usb_device_descriptor new_device_descriptor;
> +       struct usb_device_descriptor *new_device_descriptor __free(kfree) = NULL;
>         int err;
>
>         if (le16_to_cpu(get_cfg_desc(config)->wTotalLength) == EXTIGY_FIRMWARE_SIZE_OLD ||
> @@ -566,15 +566,19 @@ static int snd_usb_extigy_boot_quirk(struct usb_device *dev, struct usb_interfac
>                                       0x10, 0x43, 0x0001, 0x000a, NULL, 0);
>                 if (err < 0)
>                         dev_dbg(&dev->dev, "error sending boot message: %d\n", err);
> +
> +               new_device_descriptor = kmalloc(sizeof(*new_device_descriptor), GFP_KERNEL);
> +               if (!new_device_descriptor)
> +                       return -ENOMEM;
>                 err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
> -                               &new_device_descriptor, sizeof(new_device_descriptor));
> +                               new_device_descriptor, sizeof(*new_device_descriptor));
>                 if (err < 0)
>                         dev_dbg(&dev->dev, "error usb_get_descriptor: %d\n", err);
> -               if (new_device_descriptor.bNumConfigurations > dev->descriptor.bNumConfigurations)
> +               if (new_device_descriptor->bNumConfigurations > dev->descriptor.bNumConfigurations)
>                         dev_dbg(&dev->dev, "error too large bNumConfigurations: %d\n",
> -                               new_device_descriptor.bNumConfigurations);
> +                               new_device_descriptor->bNumConfigurations);
>                 else
> -                       memcpy(&dev->descriptor, &new_device_descriptor, sizeof(dev->descriptor));
> +                       memcpy(&dev->descriptor, new_device_descriptor, sizeof(dev->descriptor));
>                 err = usb_reset_configuration(dev);
>                 if (err < 0)
>                         dev_dbg(&dev->dev, "error usb_reset_configuration: %d\n", err);
> @@ -906,7 +910,7 @@ static void mbox2_setup_48_24_magic(struct usb_device *dev)
>  static int snd_usb_mbox2_boot_quirk(struct usb_device *dev)
>  {
>         struct usb_host_config *config = dev->actconfig;
> -       struct usb_device_descriptor new_device_descriptor;
> +       struct usb_device_descriptor *new_device_descriptor __free(kfree) = NULL;
>         int err;
>         u8 bootresponse[0x12];
>         int fwsize;
> @@ -941,15 +945,19 @@ static int snd_usb_mbox2_boot_quirk(struct usb_device *dev)
>
>         dev_dbg(&dev->dev, "device initialised!\n");
>
> +       new_device_descriptor = kmalloc(sizeof(*new_device_descriptor), GFP_KERNEL);
> +       if (!new_device_descriptor)
> +               return -ENOMEM;
> +
>         err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
> -               &new_device_descriptor, sizeof(new_device_descriptor));
> +               new_device_descriptor, sizeof(*new_device_descriptor));
>         if (err < 0)
>                 dev_dbg(&dev->dev, "error usb_get_descriptor: %d\n", err);
> -       if (new_device_descriptor.bNumConfigurations > dev->descriptor.bNumConfigurations)
> +       if (new_device_descriptor->bNumConfigurations > dev->descriptor.bNumConfigurations)
>                 dev_dbg(&dev->dev, "error too large bNumConfigurations: %d\n",
> -                       new_device_descriptor.bNumConfigurations);
> +                       new_device_descriptor->bNumConfigurations);
>         else
> -               memcpy(&dev->descriptor, &new_device_descriptor, sizeof(dev->descriptor));
> +               memcpy(&dev->descriptor, new_device_descriptor, sizeof(dev->descriptor));
>
>         err = usb_reset_configuration(dev);
>         if (err < 0)
> @@ -1259,7 +1267,7 @@ static void mbox3_setup_defaults(struct usb_device *dev)
>  static int snd_usb_mbox3_boot_quirk(struct usb_device *dev)
>  {
>         struct usb_host_config *config = dev->actconfig;
> -       struct usb_device_descriptor new_device_descriptor;
> +       struct usb_device_descriptor *new_device_descriptor __free(kfree) = NULL;
>         int err;
>         int descriptor_size;
>
> @@ -1272,15 +1280,19 @@ static int snd_usb_mbox3_boot_quirk(struct usb_device *dev)
>
>         dev_dbg(&dev->dev, "MBOX3: device initialised!\n");
>
> +       new_device_descriptor = kmalloc(sizeof(*new_device_descriptor), GFP_KERNEL);
> +       if (!new_device_descriptor)
> +               return -ENOMEM;
> +
>         err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
> -               &new_device_descriptor, sizeof(new_device_descriptor));
> +               new_device_descriptor, sizeof(*new_device_descriptor));
>         if (err < 0)
>                 dev_dbg(&dev->dev, "MBOX3: error usb_get_descriptor: %d\n", err);
> -       if (new_device_descriptor.bNumConfigurations > dev->descriptor.bNumConfigurations)
> +       if (new_device_descriptor->bNumConfigurations > dev->descriptor.bNumConfigurations)
>                 dev_dbg(&dev->dev, "MBOX3: error too large bNumConfigurations: %d\n",
> -                       new_device_descriptor.bNumConfigurations);
> +                       new_device_descriptor->bNumConfigurations);
>         else
> -               memcpy(&dev->descriptor, &new_device_descriptor, sizeof(dev->descriptor));
> +               memcpy(&dev->descriptor, new_device_descriptor, sizeof(dev->descriptor));
>
>         err = usb_reset_configuration(dev);
>         if (err < 0)
> --
> 2.45.2
>