Patch "drm/vkms: Avoid reading beyond LUT array" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    drm/vkms: Avoid reading beyond LUT array

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-vkms-avoid-reading-beyond-lut-array.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7dd38cc19ccce0cdde5b63278fcc9c1958a0660a
Author: Harry Wentland <harry.wentland@xxxxxxx>
Date:   Wed Nov 8 11:36:24 2023 -0500

    drm/vkms: Avoid reading beyond LUT array
    
    [ Upstream commit 2fee84030d12d9fddfa874e4562d71761a129277 ]
    
    When the floor LUT index (drm_fixp2int(lut_index) is the last
    index of the array the ceil LUT index will point to an entry
    beyond the array. Make sure we guard against it and use the
    value of the floor LUT index.
    
    v3:
     - Drop bits from commit description that didn't contribute
       anything of value
    
    Fixes: db1f254f2cfa ("drm/vkms: Add support to 1D gamma LUT")
    Signed-off-by: Harry Wentland <harry.wentland@xxxxxxx>
    Cc: Arthur Grillo <arthurgrillo@xxxxxxxxxx>
    Reviewed-by: Arthur Grillo <arthurgrillo@xxxxxxxxxx>
    Reviewed-by: Melissa Wen <mwen@xxxxxxxxxx>
    Signed-off-by: Melissa Wen <melissa.srw@xxxxxxxxx>
    Link: https://patchwork.freedesktop.org/patch/msgid/20231108163647.106853-6-harry.wentland@xxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
index 3c99fb8b54e2d..e7441b227b3ce 100644
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -123,6 +123,8 @@ static u16 apply_lut_to_channel_value(const struct vkms_color_lut *lut, u16 chan
 				      enum lut_channel channel)
 {
 	s64 lut_index = get_lut_index(lut, channel_value);
+	u16 *floor_lut_value, *ceil_lut_value;
+	u16 floor_channel_value, ceil_channel_value;
 
 	/*
 	 * This checks if `struct drm_color_lut` has any gap added by the compiler
@@ -130,11 +132,15 @@ static u16 apply_lut_to_channel_value(const struct vkms_color_lut *lut, u16 chan
 	 */
 	static_assert(sizeof(struct drm_color_lut) == sizeof(__u16) * 4);
 
-	u16 *floor_lut_value = (__u16 *)&lut->base[drm_fixp2int(lut_index)];
-	u16 *ceil_lut_value = (__u16 *)&lut->base[drm_fixp2int_ceil(lut_index)];
+	floor_lut_value = (__u16 *)&lut->base[drm_fixp2int(lut_index)];
+	if (drm_fixp2int(lut_index) == (lut->lut_length - 1))
+		/* We're at the end of the LUT array, use same value for ceil and floor */
+		ceil_lut_value = floor_lut_value;
+	else
+		ceil_lut_value = (__u16 *)&lut->base[drm_fixp2int_ceil(lut_index)];
 
-	u16 floor_channel_value = floor_lut_value[channel];
-	u16 ceil_channel_value = ceil_lut_value[channel];
+	floor_channel_value = floor_lut_value[channel];
+	ceil_channel_value = ceil_lut_value[channel];
 
 	return lerp_u16(floor_channel_value, ceil_channel_value,
 			lut_index & DRM_FIXED_DECIMAL_MASK);