On 14/01/2020 20:01, Takashi Iwai wrote:
> On Tue, 14 Jan 2020 16:44:12 +0100,
> Colin King wrote:
>>
>> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>>
>> It is possible for the call to snd_hda_get_num_conns to fail and return
>> a negative error code that gets assigned to num_conns. In that specific
>> case, the check of very large values of val against num_conns will not
>> fail the -EINVAL check and later on an out of bounds array read on
>> spec->smux_paths will occur. Fix this by sanity checking for an error
>> return from the call to snd_hda_get_num_conns.
>
> Thanks for the patch, but this can't happen.
> The ad1988_auto_smux_enum_put() is used only for IEC958 Playback
> Source element, and it's added in ad1988_add_spdif_mux_ctl(). And
> there at the beginning, there is already a check of the value:
>
> num_conns = snd_hda_get_num_conns(codec, 0x0b) + 1;
> if (num_conns != 3 && num_conns != 4)
> return 0;
>
> And the snd_hda_get_num_conns() function returns the cached value,
> hence it's always same at the second and later calls, so it can't be a
> negative error.
Ah, OK, sorry about the noise.
>
> That said, I don't think we need to apply the change as is. But if we
> were to improve something, we can rather record this number more
> explicitly e.g. introduce a new field spec->num_spdif_mux_conns and
> keep there instead of calling snd_hda_get_num_conns() at each place.
That would seem more optimal for sure.
Colin
>
>
> thanks,
>
> Takashi
>
>>
>> Addresses-Coverity: ("Out-of-bounds read")
>> Fixes: 272f3ea31776 ("ALSA: hda - Add SPDIF mux control to AD codec auto-parser")
>> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>> ---
>> sound/pci/hda/patch_analog.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/sound/pci/hda/patch_analog.c b/sound/pci/hda/patch_analog.c
>> index 88c46b051d14..399561369495 100644
>> --- a/sound/pci/hda/patch_analog.c
>> +++ b/sound/pci/hda/patch_analog.c
>> @@ -756,9 +756,11 @@ static int ad1988_auto_smux_enum_put(struct snd_kcontrol *kcontrol,
>> struct ad198x_spec *spec = codec->spec;
>> unsigned int val = ucontrol->value.enumerated.item[0];
>> struct nid_path *path;
>> - int num_conns = snd_hda_get_num_conns(codec, 0x0b) + 1;
>> + int num_conns = snd_hda_get_num_conns(codec, 0x0b);
>>
>> - if (val >= num_conns)
>> + if (num_conns < 0)
>> + return num_conns;
>> + if (val >= num_conns + 1)
>> return -EINVAL;
>> if (spec->cur_smux == val)
>> return 0;
>> --
>> 2.24.0
>>
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