This is the backported patch for the following fix to v4.4.x and v4.14.x:
19bce474c45b ("ALSA: usb-audio: Fix a stack buffer overflow bug in
check_input_term")
On Fri, Aug 30, 2019 at 5:47 PM Hui Peng <benquike@xxxxxxxxx> wrote:
> `check_input_term` recursively calls itself with input from
> device side (e.g., uac_input_terminal_descriptor.bCSourceID)
> as argument (id). In `check_input_term`, if `check_input_term`
> is called with the same `id` argument as the caller, it triggers
> endless recursive call, resulting kernel space stack overflow.
>
> This patch fixes the bug by adding a bitmap to `struct mixer_build`
> to keep track of the checked ids and stop the execution if some id
> has been checked (similar to how parse_audio_unit handles unitid
> argument).
>
> CVE: CVE-2018-15118
>
> Reported-by: Hui Peng <benquike@xxxxxxxxx>
> Reported-by: Mathias Payer <mathias.payer@xxxxxxxxxxxxx>
> Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
> ---
> sound/usb/mixer.c | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index 10ddec76f906..e24572fd6e30 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -81,6 +81,7 @@ struct mixer_build {
> unsigned char *buffer;
> unsigned int buflen;
> DECLARE_BITMAP(unitbitmap, MAX_ID_ELEMS);
> + DECLARE_BITMAP(termbitmap, MAX_ID_ELEMS);
> struct usb_audio_term oterm;
> const struct usbmix_name_map *map;
> const struct usbmix_selector_map *selector_map;
> @@ -709,15 +710,24 @@ static int get_term_name(struct mixer_build *state,
> struct usb_audio_term *iterm
> * parse the source unit recursively until it reaches to a terminal
> * or a branched unit.
> */
> -static int check_input_term(struct mixer_build *state, int id,
> +static int __check_input_term(struct mixer_build *state, int id,
> struct usb_audio_term *term)
> {
> int err;
> void *p1;
> + unsigned char *hdr;
>
> memset(term, 0, sizeof(*term));
> - while ((p1 = find_audio_control_unit(state, id)) != NULL) {
> - unsigned char *hdr = p1;
> + for (;;) {
> + /* a loop in the terminal chain? */
> + if (test_and_set_bit(id, state->termbitmap))
> + return -EINVAL;
> +
> + p1 = find_audio_control_unit(state, id);
> + if (!p1)
> + break;
> +
> + hdr = p1;
> term->id = id;
> switch (hdr[2]) {
> case UAC_INPUT_TERMINAL:
> @@ -732,7 +742,7 @@ static int check_input_term(struct mixer_build *state,
> int id,
>
> /* call recursively to verify that the
> * referenced clock entity is valid */
> - err = check_input_term(state,
> d->bCSourceID, term);
> + err = __check_input_term(state,
> d->bCSourceID, term);
> if (err < 0)
> return err;
>
> @@ -764,7 +774,7 @@ static int check_input_term(struct mixer_build *state,
> int id,
> case UAC2_CLOCK_SELECTOR: {
> struct uac_selector_unit_descriptor *d = p1;
> /* call recursively to retrieve the channel info */
> - err = check_input_term(state, d->baSourceID[0],
> term);
> + err = __check_input_term(state, d->baSourceID[0],
> term);
> if (err < 0)
> return err;
> term->type = d->bDescriptorSubtype << 16; /*
> virtual type */
> @@ -811,6 +821,15 @@ static int check_input_term(struct mixer_build
> *state, int id,
> return -ENODEV;
> }
>
> +
> +static int check_input_term(struct mixer_build *state, int id,
> + struct usb_audio_term *term)
> +{
> + memset(term, 0, sizeof(*term));
> + memset(state->termbitmap, 0, sizeof(state->termbitmap));
> + return __check_input_term(state, id, term);
> +}
> +
> /*
> * Feature Unit
> */
> --
> 2.17.1
>
>
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