[alsa-devel] [PATCH 1/2] ALSA: usb-audio: Avoid access before bLength check in build_audio_procunit()
The parser for the processing unit reads bNrInPins field before the bLength sanity check, which may lead to an out-of-bound access when a malformed descriptor is given. Fix it by assignment after the bLength check.
Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/usb/mixer.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c index c63c84b54969..0131de348cf6 100644 --- a/sound/usb/mixer.c +++ b/sound/usb/mixer.c @@ -2314,7 +2314,7 @@ static int build_audio_procunit(struct mixer_build *state, int unitid, char *name) { struct uac_processing_unit_descriptor *desc = raw_desc; - int num_ins = desc->bNrInPins; + int num_ins; struct usb_mixer_elem_info *cval; struct snd_kcontrol *kctl; int i, err, nameid, type, len; @@ -2329,7 +2329,13 @@ static int build_audio_procunit(struct mixer_build *state, int unitid, 0, NULL, default_value_info };
- if (desc->bLength < 13 || desc->bLength < 13 + num_ins || + if (desc->bLength < 13) { + usb_audio_err(state->chip, "invalid %s descriptor (id %d)\n", name, unitid); + return -EINVAL; + } + + num_ins = desc->bNrInPins; + if (desc->bLength < 13 + num_ins || desc->bLength < num_ins + uac_processing_unit_bControlSize(desc, state->mixer->protocol)) { usb_audio_err(state->chip, "invalid %s descriptor (id %d)\n", name, unitid); return -EINVAL;
We've had some sanity checks of the mixer unit descriptors but they are too loose and some corner cases are overlooked. Add more strict checks in uac_mixer_unit_get_channels() for avoiding possible OOB accesses by malformed descriptors.
This also changes the semantics of uac_mixer_unit_get_channels() slightly. Now it returns zero for the cases where the descriptor lacks of bmControls instead of -EINVAL. Then the caller side skips the mixer creation for such unit while it keeps parsing it. This corresponds to the case like Maya44.
Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/usb/mixer.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c index 0131de348cf6..dfd918891e69 100644 --- a/sound/usb/mixer.c +++ b/sound/usb/mixer.c @@ -753,8 +753,9 @@ static int uac_mixer_unit_get_channels(struct mixer_build *state, struct uac_mixer_unit_descriptor *desc) { int mu_channels; + void *c;
- if (desc->bLength < 11) + if (desc->bLength < sizeof(*desc)) return -EINVAL; if (!desc->bNrInPins) return -EINVAL; @@ -763,6 +764,8 @@ static int uac_mixer_unit_get_channels(struct mixer_build *state, case UAC_VERSION_1: case UAC_VERSION_2: default: + if (desc->bLength < sizeof(*desc) + desc->bNrInPins + 1) + return 0; /* no bmControls -> skip */ mu_channels = uac_mixer_unit_bNrChannels(desc); break; case UAC_VERSION_3: @@ -772,7 +775,11 @@ static int uac_mixer_unit_get_channels(struct mixer_build *state, }
if (!mu_channels) - return -EINVAL; + return 0; + + c = uac_mixer_unit_bmControls(desc, state->mixer->protocol); + if (c - (void *)desc + (mu_channels - 1) / 8 >= desc->bLength) + return 0; /* no bmControls -> skip */
return mu_channels; } @@ -944,7 +951,7 @@ static int check_input_term(struct mixer_build *state, int id, struct uac_mixer_unit_descriptor *d = p1;
err = uac_mixer_unit_get_channels(state, d); - if (err < 0) + if (err <= 0) return err;
term->channels = err; @@ -2118,7 +2125,7 @@ static int parse_audio_mixer_unit(struct mixer_build *state, int unitid, if (err < 0) continue; /* no bmControls field (e.g. Maya44) -> ignore */ - if (desc->bLength <= 10 + input_pins) + if (!num_outs) continue; err = check_input_term(state, desc->baSourceID[pin], &iterm); if (err < 0)
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Takashi Iwai