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    Subject[PATCH 5.10 191/563] backlight: qcom-wled: Fix off-by-one maximum with default num_strings
    Date
    From: Marijn Suijten <marijn.suijten@somainline.org>

    [ Upstream commit 5ada78b26f935f8751852dffa24f6b545b1d2517 ]

    When not specifying num-strings in the DT the default is used, but +1 is
    added to it which turns WLED3 into 4 and WLED4/5 into 5 strings instead
    of 3 and 4 respectively, causing out-of-bounds reads and register
    read/writes. This +1 exists for a deficiency in the DT parsing code,
    and is simply omitted entirely - solving this oob issue - by parsing the
    property separately much like qcom,enabled-strings.

    This also enables more stringent checks on the maximum value when
    qcom,enabled-strings is provided in the DT, by parsing num-strings after
    enabled-strings to allow it to check against (and in a subsequent patch
    override) the length of enabled-strings: it is invalid to set
    num-strings higher than that.
    The DT currently utilizes it to get around an incorrect fixed read of
    four elements from that array (has been addressed in a prior patch) by
    setting a lower num-strings where desired.

    Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
    Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
    Reviewed-By: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
    Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
    Signed-off-by: Lee Jones <lee.jones@linaro.org>
    Link: https://lore.kernel.org/r/20211115203459.1634079-5-marijn.suijten@somainline.org
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/video/backlight/qcom-wled.c | 48 ++++++++++-------------------
    1 file changed, 16 insertions(+), 32 deletions(-)

    diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
    index 92df5a9f6ae51..9e09165984b48 100644
    --- a/drivers/video/backlight/qcom-wled.c
    +++ b/drivers/video/backlight/qcom-wled.c
    @@ -1256,21 +1256,6 @@ static const struct wled_var_cfg wled5_ovp_cfg = {
    .size = 16,
    };

    -static u32 wled3_num_strings_values_fn(u32 idx)
    -{
    - return idx + 1;
    -}
    -
    -static const struct wled_var_cfg wled3_num_strings_cfg = {
    - .fn = wled3_num_strings_values_fn,
    - .size = 3,
    -};
    -
    -static const struct wled_var_cfg wled4_num_strings_cfg = {
    - .fn = wled3_num_strings_values_fn,
    - .size = 4,
    -};
    -
    static u32 wled3_switch_freq_values_fn(u32 idx)
    {
    return 19200 / (2 * (1 + idx));
    @@ -1344,11 +1329,6 @@ static int wled_configure(struct wled *wled)
    .val_ptr = &cfg->switch_freq,
    .cfg = &wled3_switch_freq_cfg,
    },
    - {
    - .name = "qcom,num-strings",
    - .val_ptr = &cfg->num_strings,
    - .cfg = &wled3_num_strings_cfg,
    - },
    };

    const struct wled_u32_opts wled4_opts[] = {
    @@ -1372,11 +1352,6 @@ static int wled_configure(struct wled *wled)
    .val_ptr = &cfg->switch_freq,
    .cfg = &wled3_switch_freq_cfg,
    },
    - {
    - .name = "qcom,num-strings",
    - .val_ptr = &cfg->num_strings,
    - .cfg = &wled4_num_strings_cfg,
    - },
    };

    const struct wled_u32_opts wled5_opts[] = {
    @@ -1400,11 +1375,6 @@ static int wled_configure(struct wled *wled)
    .val_ptr = &cfg->switch_freq,
    .cfg = &wled3_switch_freq_cfg,
    },
    - {
    - .name = "qcom,num-strings",
    - .val_ptr = &cfg->num_strings,
    - .cfg = &wled4_num_strings_cfg,
    - },
    {
    .name = "qcom,modulator-sel",
    .val_ptr = &cfg->mod_sel,
    @@ -1523,8 +1493,6 @@ static int wled_configure(struct wled *wled)
    *bool_opts[i].val_ptr = true;
    }

    - cfg->num_strings = cfg->num_strings + 1;
    -
    string_len = of_property_count_elems_of_size(dev->of_node,
    "qcom,enabled-strings",
    sizeof(u32));
    @@ -1555,6 +1523,22 @@ static int wled_configure(struct wled *wled)
    }
    }

    + rc = of_property_read_u32(dev->of_node, "qcom,num-strings", &val);
    + if (!rc) {
    + if (val < 1 || val > wled->max_string_count) {
    + dev_err(dev, "qcom,num-strings must be between 1 and %d\n",
    + wled->max_string_count);
    + return -EINVAL;
    + }
    +
    + if (string_len > 0 && val > string_len) {
    + dev_err(dev, "qcom,num-strings exceeds qcom,enabled-strings\n");
    + return -EINVAL;
    + }
    +
    + cfg->num_strings = val;
    + }
    +
    return 0;
    }

    --
    2.34.1


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