ALSA: usb-audio: Fix a stack buffer overflow bug in check_input_term

`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).

Reported-by: Hui Peng <benquike@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Signed-off-by: Hui Peng <benquike@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 27 insertions, 8 deletions

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ea487378be17..b5927c3d5bc0 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -68,6 +68,7 @@ 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;
@@ -775,16 +776,25 @@ static int uac_mixer_unit_get_channels(struct mixer_build *state,
  * 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 protocol = state->mixer->protocol;
         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;
 
                 if (protocol == UAC_VERSION_1 || protocol == UAC_VERSION_2) {
@@ -802,7 +812,7 @@ 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;
 
@@ -836,7 +846,7 @@ 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 = UAC3_SELECTOR_UNIT << 16; /* virtual type */
@@ -899,7 +909,7 @@ 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;
 
@@ -950,7 +960,7 @@ static int check_input_term(struct mixer_build *state, int id,
                         case UAC3_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 = UAC3_SELECTOR_UNIT << 16; /* virtual type */
@@ -966,7 +976,7 @@ static int check_input_term(struct mixer_build *state, int id,
                                         return -EINVAL;
 
                                 /* 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;
 
@@ -984,6 +994,15 @@ 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
  */