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From 558c69b5d36d14d55bff21e6570205fe73a02ca2 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Tue, 6 Jul 2021 18:51:35 +1000
Subject: video/readers/png: Drop greyscale support to fix heap out-of-bounds
write
A 16-bit greyscale PNG without alpha is processed in the following loop:
for (i = 0; i < (data->image_width * data->image_height);
i++, d1 += 4, d2 += 2)
{
d1[R3] = d2[1];
d1[G3] = d2[1];
d1[B3] = d2[1];
}
The increment of d1 is wrong. d1 is incremented by 4 bytes per iteration,
but there are only 3 bytes allocated for storage. This means that image
data will overwrite somewhat-attacker-controlled parts of memory - 3 bytes
out of every 4 following the end of the image.
This has existed since greyscale support was added in 2013 in commit
3ccf16dff98f (grub-core/video/readers/png.c: Support grayscale).
Saving starfield.png as a 16-bit greyscale image without alpha in the gimp
and attempting to load it causes grub-emu to crash - I don't think this code
has ever worked.
Delete all PNG greyscale support.
Fixes: CVE-2021-3695
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/video/readers/png.c | 87 +++--------------------------------
1 file changed, 7 insertions(+), 80 deletions(-)
diff --git a/grub-core/video/readers/png.c b/grub-core/video/readers/png.c
index 8955b8ecf..a3161e25b 100644
--- a/grub-core/video/readers/png.c
+++ b/grub-core/video/readers/png.c
@@ -100,7 +100,7 @@ struct grub_png_data
unsigned image_width, image_height;
int bpp, is_16bit;
- int raw_bytes, is_gray, is_alpha, is_palette;
+ int raw_bytes, is_alpha, is_palette;
int row_bytes, color_bits;
grub_uint8_t *image_data;
@@ -296,13 +296,13 @@ grub_png_decode_image_header (struct grub_png_data *data)
data->bpp = 3;
else
{
- data->is_gray = 1;
- data->bpp = 1;
+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+ "png: color type not supported");
}
if ((color_bits != 8) && (color_bits != 16)
&& (color_bits != 4
- || !(data->is_gray || data->is_palette)))
+ || !data->is_palette))
return grub_error (GRUB_ERR_BAD_FILE_TYPE,
"png: bit depth must be 8 or 16");
@@ -331,7 +331,7 @@ grub_png_decode_image_header (struct grub_png_data *data)
}
#ifndef GRUB_CPU_WORDS_BIGENDIAN
- if (data->is_16bit || data->is_gray || data->is_palette)
+ if (data->is_16bit || data->is_palette)
#endif
{
data->image_data = grub_calloc (data->image_height, data->row_bytes);
@@ -899,27 +899,8 @@ grub_png_convert_image (struct grub_png_data *data)
int shift;
int mask = (1 << data->color_bits) - 1;
unsigned j;
- if (data->is_gray)
- {
- /* Generic formula is
- (0xff * i) / ((1U << data->color_bits) - 1)
- but for allowed bit depth of 1, 2 and for it's
- equivalent to
- (0xff / ((1U << data->color_bits) - 1)) * i
- Precompute the multipliers to avoid division.
- */
-
- const grub_uint8_t multipliers[5] = { 0xff, 0xff, 0x55, 0x24, 0x11 };
- for (i = 0; i < (1U << data->color_bits); i++)
- {
- grub_uint8_t col = multipliers[data->color_bits] * i;
- palette[i][0] = col;
- palette[i][1] = col;
- palette[i][2] = col;
- }
- }
- else
- grub_memcpy (palette, data->palette, 3 << data->color_bits);
+
+ grub_memcpy (palette, data->palette, 3 << data->color_bits);
d1c = d1;
d2c = d2;
for (j = 0; j < data->image_height; j++, d1c += data->image_width * 3,
@@ -956,60 +937,6 @@ grub_png_convert_image (struct grub_png_data *data)
}
return;
}
-
- if (data->is_gray)
- {
- switch (data->bpp)
- {
- case 4:
- /* 16-bit gray with alpha. */
- for (i = 0; i < (data->image_width * data->image_height);
- i++, d1 += 4, d2 += 4)
- {
- d1[R4] = d2[3];
- d1[G4] = d2[3];
- d1[B4] = d2[3];
- d1[A4] = d2[1];
- }
- break;
- case 2:
- if (data->is_16bit)
- /* 16-bit gray without alpha. */
- {
- for (i = 0; i < (data->image_width * data->image_height);
- i++, d1 += 4, d2 += 2)
- {
- d1[R3] = d2[1];
- d1[G3] = d2[1];
- d1[B3] = d2[1];
- }
- }
- else
- /* 8-bit gray with alpha. */
- {
- for (i = 0; i < (data->image_width * data->image_height);
- i++, d1 += 4, d2 += 2)
- {
- d1[R4] = d2[1];
- d1[G4] = d2[1];
- d1[B4] = d2[1];
- d1[A4] = d2[0];
- }
- }
- break;
- /* 8-bit gray without alpha. */
- case 1:
- for (i = 0; i < (data->image_width * data->image_height);
- i++, d1 += 3, d2++)
- {
- d1[R3] = d2[0];
- d1[G3] = d2[0];
- d1[B3] = d2[0];
- }
- break;
- }
- return;
- }
{
/* Only copy the upper 8 bit. */
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