On Fri, Dec 20, 2019 at 10:46:50AM +0100, Takashi Iwai wrote:
On Fri, 20 Dec 2019 10:31:34 +0100, Johan Hovold wrote:
Make sure to check the return value of usb_altnum_to_altsetting() to avoid dereferencing a NULL pointer when the requested alternate settings is missing.
The format altsetting number may come from a quirk table and there does not seem to be any other validation of it (the corresponding index is checked however).
Fixes: b099b9693d23 ("ALSA: usb-audio: Avoid superfluous usb_set_interface() calls") Cc: stable stable@vger.kernel.org # 4.18 Signed-off-by: Johan Hovold johan@kernel.org
sound/usb/pcm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c index 9c8930bb00c8..73dd9d21bb42 100644 --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -506,9 +506,9 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt) if (WARN_ON(!iface)) return -EINVAL; alts = usb_altnum_to_altsetting(iface, fmt->altsetting);
- altsd = get_iface_desc(alts);
- if (WARN_ON(altsd->bAlternateSetting != fmt->altsetting))
- if (WARN_ON(!alts)) return -EINVAL;
Do we need WARN_ON() here? If this may hit on syzbot, it'll stop at this point because of panic_on_warn.
Yeah, I considered that too and decided to leave it in. Just like for the WARN_ON(iface), those numbers should be verified at probe.
I tried tracking where fmt->altsetting comes from, and it seems like a sanity check needs to be added at least to create_fixed_stream_quirk() where, for example, fmt->iface, fmt->altset_idx and the number of endpoints are verified.
If there are other paths that can end up setting these fields to invalid values, we want that WARN_ON() in there so we can fix those.
Johan