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Subject[PATCH 4.4 57/77] ALSA: usb-audio: Fix a stack buffer overflow bug in check_input_term
Date
From: Hui Peng <benquike@gmail.com>

commit 19bce474c45be69a284ecee660aa12d8f1e88f18 upstream.

`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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


---
sound/usb/mixer.c | 29 ++++++++++++++++++++++++-----
1 file changed, 24 insertions(+), 5 deletions(-)

--- 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_bu
* 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

/* 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
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
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
*/

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