dany/libwebp
1
0
Fork 0
mirror of https://github.com/webmproject/libwebp.git synced 2025-10-31 18:35:41 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity

near_lossless: fix fuzzing-detected integer overflow

Browse Source 
It's safer to clip the passed param instead of doing 32b arithmetic
and clipping afterward.

Output is unchanged, but code no longer rely on UB.

Change-Id: Ia5b4de6e8863981753f1d17f062965a6a5da5bed
This commit is contained in:
Skal
2019-01-05 17:40:50 +01:00
committed by Pascal Massimino
parent 928a75deca
commit aec2cf02d1
1 changed files with 8 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
src/enc/predictor_enc.c
View File

@@ -177,12 +177,15 @@ static uint8_t NearLosslessComponent(uint8_t value, uint8_t predict,
}
}
static WEBP_INLINE uint8_t NearLosslessDiff(uint8_t a, uint8_t b) {
return (uint8_t)((((int)(a) - (int)(b))) & 0xff);
}
// Quantize every component of the difference between the actual pixel value and
// its prediction to a multiple of a quantization (a power of 2, not larger than
// max_quantization which is a power of 2, smaller than max_diff). Take care if
// value and predict have undergone subtract green, which means that red and
// blue are represented as offsets from green.
#define NEAR_LOSSLESS_DIFF(a, b) (uint8_t)((((int)(a) - (int)(b))) & 0xff)
static uint32_t NearLossless(uint32_t value, uint32_t predict,
int max_quantization, int max_diff,
int used_subtract_green) {
@@ -199,7 +202,7 @@ static uint32_t NearLossless(uint32_t value, uint32_t predict,
}
if ((value >> 24) == 0 || (value >> 24) == 0xff) {
// Preserve transparency of fully transparent or fully opaque pixels.
a = NEAR_LOSSLESS_DIFF(value >> 24, predict >> 24);
a = NearLosslessDiff(value >> 24, predict >> 24);
} else {
a = NearLosslessComponent(value >> 24, predict >> 24, 0xff, quantization);
}
@@ -212,16 +215,15 @@ static uint32_t NearLossless(uint32_t value, uint32_t predict,
// The amount by which green has been adjusted during quantization. It is
// subtracted from red and blue for compensation, to avoid accumulating two
// quantization errors in them.
green_diff = NEAR_LOSSLESS_DIFF(new_green, value >> 8);
green_diff = NearLosslessDiff(new_green, value >> 8);
}
r = NearLosslessComponent(NEAR_LOSSLESS_DIFF(value >> 16, green_diff),
r = NearLosslessComponent(NearLosslessDiff(value >> 16, green_diff),
(predict >> 16) & 0xff, 0xff - new_green,
quantization);
b = NearLosslessComponent(NEAR_LOSSLESS_DIFF(value, green_diff),
b = NearLosslessComponent(NearLosslessDiff(value, green_diff),
predict & 0xff, 0xff - new_green, quantization);
return ((uint32_t)a << 24) | ((uint32_t)r << 16) | ((uint32_t)g << 8) | b;
}
#undef NEAR_LOSSLESS_DIFF
#endif // (WEBP_NEAR_LOSSLESS == 1)
// Stores the difference between the pixel and its prediction in "out".