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    Subject[PATCH AUTOSEL 4.14 011/186] ALSA: ctl: allow TLV read operation for callback type of element in locked case
    Date
    From: Takashi Sakamoto <o-takashi@sakamocchi.jp>

    [ Upstream commit d61fe22c2ae42d9fd76c34ef4224064cca4b04b0 ]

    A design of ALSA control core allows applications to execute three
    operations for TLV feature; read, write and command. Furthermore, it
    allows driver developers to process the operations by two ways; allocated
    array or callback function. In the former, read operation is just allowed,
    thus developers uses the latter when device driver supports variety of
    models or the target model is expected to dynamically change information
    stored in TLV container.

    The core also allows applications to lock any element so that the other
    applications can't perform write operation to the element for element
    value and TLV information. When the element is locked, write and command
    operation for TLV information are prohibited as well as element value.
    Any read operation should be allowed in the case.

    At present, when an element has callback function for TLV information,
    TLV read operation returns EPERM if the element is locked. On the
    other hand, the read operation is success when an element has allocated
    array for TLV information. In both cases, read operation is success for
    element value expectedly.

    This commit fixes the bug. This change can be backported to v4.14
    kernel or later.

    Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
    Reviewed-by: Jaroslav Kysela <perex@perex.cz>
    Link: https://lore.kernel.org/r/20191223093347.15279-1-o-takashi@sakamocchi.jp
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    sound/core/control.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/sound/core/control.c b/sound/core/control.c
    index 36571cd49be33..a0ce22164957c 100644
    --- a/sound/core/control.c
    +++ b/sound/core/control.c
    @@ -1467,8 +1467,9 @@ static int call_tlv_handler(struct snd_ctl_file *file, int op_flag,
    if (kctl->tlv.c == NULL)
    return -ENXIO;

    - /* When locked, this is unavailable. */
    - if (vd->owner != NULL && vd->owner != file)
    + /* Write and command operations are not allowed for locked element. */
    + if (op_flag != SNDRV_CTL_TLV_OP_READ &&
    + vd->owner != NULL && vd->owner != file)
    return -EPERM;

    return kctl->tlv.c(kctl, op_flag, size, buf);
    --
    2.20.1
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