Hi, Takashi:
Thanks for the guide.
The new patch is confirmed and attached.
On Wed, Aug 14, 2019 at 12:33 PM Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Wed, 14 Aug 2019 18:28:39 +0200,
> 彭辉 wrote:
> >
> > Hi, Takashi:
> > Here the problem is that `desc->bLength` is controlled by the device
> side,
> > so `desc->bLength` may not represent the real length of the descriptor.
> > That is why I use pointer arithmetic operations to derive the real size
> of the
> > buffer
> > in my patch.
>
> But bLength is checked before calling this, i.e. it's already assured
> that bLength fits within the buffer limit. So, the result calls don't
> have to care about the buffer limit itself, and they can just
> concentrate on overflow over bLength.
>
>
> thanks,
>
> Takashi
>
> >
> > On Wed, Aug 14, 2019 at 2:36 AM Takashi Iwai <tiwai@xxxxxxx> wrote:
> >
> > On Wed, 14 Aug 2019 04:36:24 +0200,
> > Hui Peng wrote:
> > >
> > > The `uac_mixer_unit_descriptor` shown as below is read from the
> > > device side. In `parse_audio_mixer_unit`, `baSourceID` field is
> > > accessed from index 0 to `bNrInPins` - 1, the current
> implementation
> > > assumes that descriptor is always valid (the length of descriptor
> > > is no shorter than 5 + `bNrInPins`). If a descriptor read from
> > > the device side is invalid, it may trigger out-of-bound memory
> > > access.
> > >
> > > ```
> > > struct uac_mixer_unit_descriptor {
> > > __u8 bLength;
> > > __u8 bDescriptorType;
> > > __u8 bDescriptorSubtype;
> > > __u8 bUnitID;
> > > __u8 bNrInPins;
> > > __u8 baSourceID[];
> > > }
> > > ```
> > >
> > > This patch fixes the bug by add a sanity check on the length of
> > > the descriptor.
> > >
> > > Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
> > > Reported-by: Hui Peng <benquike@xxxxxxxxx>
> > > Reported-by: Mathias Payer <mathias.payer@xxxxxxxxxxxxx>
> > > ---
> > > sound/usb/mixer.c | 9 +++++++++
> > > 1 file changed, 9 insertions(+)
> > >
> > > diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> > > index 7498b5191b68..38202ce67237 100644
> > > --- a/sound/usb/mixer.c
> > > +++ b/sound/usb/mixer.c
> > > @@ -2091,6 +2091,15 @@ static int parse_audio_mixer_unit(struct
> > mixer_build *state, int unitid,
> > > struct usb_audio_term iterm;
> > > int input_pins, num_ins, num_outs;
> > > int pin, ich, err;
> > > + int desc_len = (int) ((unsigned long) state->buffer +
> > > + state->buflen - (unsigned long) raw_desc);
> > > +
> > > + if (desc_len < sizeof(*desc) + desc->bNrInPins) {
> > > + usb_audio_err(state->chip,
> > > + "descriptor %d too short\n",
> > > + unitid);
> > > + return -EINVAL;
> > > + }
> > >
> > > err = uac_mixer_unit_get_channels(state, desc);
> > > if (err < 0) {
> >
> > Hm, what is the desc->bLength value in the error case?
> >
> > Basically the buffer boundary is already checked against bLength in
> > snd_usb_find_desc() which is called from obtaining the raw_desc in
> the
> > caller of this function (parse_audio_unit()).
> >
> > So, if any, we need to check bLength for the possible overflow like
> > below.
> >
> > thanks,
> >
> > Takashi
> >
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -744,6 +744,8 @@ static int uac_mixer_unit_get_channels(struct
> > mixer_build *state,
> > return -EINVAL;
> > if (!desc->bNrInPins)
> > return -EINVAL;
> > + if (desc->bLength < sizeof(*desc) + desc->bNrInPins)
> > + return -EINVAL;
> >
> > switch (state->mixer->protocol) {
> > case UAC_VERSION_1:
> >
> > --
> > May the Lord Richly Bless you and yours !
> >
> >
>
--
May the *Lord* Richly Bless you and yours !
From da17e2db04d29d39f3298738badd036cf3f256d2 Mon Sep 17 00:00:00 2001
From: Hui Peng <benquike@xxxxxxxxx>
Date: Tue, 13 Aug 2019 22:34:04 -0400
Subject: [PATCH] Fix an OOB bug in parse_audio_mixer_unit
The `uac_mixer_unit_descriptor` shown as below is read from the
device side. In `parse_audio_mixer_unit`, `baSourceID` field is
accessed from index 0 to `bNrInPins` - 1, the current implementation
assumes that descriptor is always valid (the length of descriptor
is no shorter than 5 + `bNrInPins`). If a descriptor read from
the device side is invalid, it may trigger out-of-bound memory
access.
```
struct uac_mixer_unit_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 bDescriptorSubtype;
__u8 bUnitID;
__u8 bNrInPins;
__u8 baSourceID[];
}
```
This patch fixes the bug by add a sanity check on the length of
the descriptor.
Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
Reported-by: Hui Peng <benquike@xxxxxxxxx>
Reported-by: Mathias Payer <mathias.payer@xxxxxxxxxxxxx>
---
sound/usb/mixer.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 7498b5191b68..ea487378be17 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -744,6 +744,8 @@ static int uac_mixer_unit_get_channels(struct mixer_build *state,
return -EINVAL;
if (!desc->bNrInPins)
return -EINVAL;
+ if (desc->bLength < sizeof(*desc) + desc->bNrInPins)
+ return -EINVAL;
switch (state->mixer->protocol) {
case UAC_VERSION_1:
--
2.22.1
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