Commit 5ada78b2 authored by Marijn Suijten's avatar Marijn Suijten Committed by Lee Jones
Browse files

backlight: qcom-wled: Fix off-by-one maximum with default num_strings 



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: 93c64f1e ("leds: add Qualcomm PM8941 WLED driver")
Signed-off-by: default avatarMarijn Suijten <marijn.suijten@somainline.org>
Reviewed-By: default avatarAngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Reviewed-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: default avatarLee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211115203459.1634079-5-marijn.suijten@somainline.org
parent 0a139358

drivers/video/backlight/qcom-wled.c

+16 −32
Original line number Diff line number Diff line
@@ -1255,21 +1255,6 @@ 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));
@@ -1343,11 +1328,6 @@ 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[] = {
@@ -1371,11 +1351,6 @@ 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[] = {
@@ -1399,11 +1374,6 @@ 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,
@@ -1522,8 +1492,6 @@ 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));
@@ -1554,6 +1522,22 @@ 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;

}