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129 lines
3.9 KiB
Objective-C
129 lines
3.9 KiB
Objective-C
//
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// Copyright (c) 2017 Open Whisper Systems. All rights reserved.
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//
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#import "NSData+Image.h"
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typedef NS_ENUM(NSInteger, ImageFormat) {
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ImageFormat_Unknown,
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ImageFormat_Png,
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ImageFormat_Gif,
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ImageFormat_Tiff,
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ImageFormat_Jpeg,
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ImageFormat_Bmp,
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};
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@implementation NSData (Image)
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+ (BOOL)ows_isValidImageAtPath:(NSString *)filePath
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{
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NSError *error = nil;
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NSData *data = [NSData dataWithContentsOfFile:filePath options:NSDataReadingMappedIfSafe error:&error];
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if (error) {
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DDLogError(@"%@ could not read image data: %@", self.logTag, error);
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}
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return [data ows_isValidImage];
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}
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- (BOOL)ows_isValidImage
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{
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// Don't trust the file extension; iOS (e.g. UIKit, Core Graphics) will happily
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// load a .gif with a .png file extension.
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//
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// Instead, use the "magic numbers" in the file data to determine the image format.
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ImageFormat imageFormat = [self ows_guessImageFormat];
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if (imageFormat == ImageFormat_Gif) {
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return [self ows_hasValidGifSize];
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} else if (imageFormat == ImageFormat_Unknown) {
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return NO;
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} else {
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return YES;
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}
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}
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- (ImageFormat)ows_guessImageFormat
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{
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const NSUInteger kTwoBytesLength = 2;
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if (self.length < kTwoBytesLength) {
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return ImageFormat_Unknown;
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}
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unsigned char bytes[kTwoBytesLength];
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[self getBytes:&bytes range:NSMakeRange(0, kTwoBytesLength)];
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unsigned char byte0 = bytes[0];
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unsigned char byte1 = bytes[1];
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if (byte0 == 0x47 && byte1 == 0x49) {
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return ImageFormat_Gif;
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} else if (byte0 == 0x89 && byte1 == 0x50) {
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return ImageFormat_Png;
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} else if (byte0 == 0xff && byte1 == 0xd8) {
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return ImageFormat_Jpeg;
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} else if (byte0 == 0x42 && byte1 == 0x4d) {
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return ImageFormat_Bmp;
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} else if (byte0 == 0x4D && byte1 == 0x4D) {
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// Motorola byte order TIFF
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return ImageFormat_Tiff;
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} else if (byte0 == 0x49 && byte1 == 0x49) {
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// Intel byte order TIFF
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return ImageFormat_Tiff;
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}
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return ImageFormat_Unknown;
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}
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+ (BOOL)ows_areByteArraysEqual:(NSUInteger)length left:(unsigned char *)left right:(unsigned char *)right
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{
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for (NSUInteger i = 0; i < length; i++) {
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if (left[i] != right[i]) {
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return NO;
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}
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}
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return YES;
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}
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// Parse the GIF header to prevent the "GIF of death" issue.
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//
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// See: https://blog.flanker017.me/cve-2017-2416-gif-remote-exec/
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// See: https://www.w3.org/Graphics/GIF/spec-gif89a.txt
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- (BOOL)ows_hasValidGifSize
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{
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const NSUInteger kSignatureLength = 3;
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const NSUInteger kVersionLength = 3;
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const NSUInteger kWidthLength = 2;
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const NSUInteger kHeightLength = 2;
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const NSUInteger kPrefixLength = kSignatureLength + kVersionLength;
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const NSUInteger kBufferLength = kSignatureLength + kVersionLength + kWidthLength + kHeightLength;
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if (self.length < kBufferLength) {
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return NO;
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}
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unsigned char bytes[kBufferLength];
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[self getBytes:&bytes range:NSMakeRange(0, kBufferLength)];
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unsigned char kGif87APrefix[kPrefixLength] = {
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0x47, 0x49, 0x46, 0x38, 0x37, 0x61,
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};
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unsigned char kGif89APrefix[kPrefixLength] = {
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0x47, 0x49, 0x46, 0x38, 0x39, 0x61,
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};
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if (![NSData ows_areByteArraysEqual:kPrefixLength left:bytes right:kGif87APrefix]
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&& ![NSData ows_areByteArraysEqual:kPrefixLength left:bytes right:kGif89APrefix]) {
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return NO;
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}
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NSUInteger width = ((NSUInteger)bytes[kPrefixLength + 0]) | (((NSUInteger)bytes[kPrefixLength + 1] << 8));
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NSUInteger height = ((NSUInteger)bytes[kPrefixLength + 2]) | (((NSUInteger)bytes[kPrefixLength + 3] << 8));
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// We need to ensure that the image size is "reasonable".
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// We impose an arbitrary "very large" limit on image size
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// to eliminate harmful values.
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const NSUInteger kMaxValidSize = 1 << 18;
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return (width > 0 && width < kMaxValidSize && height > 0 && height < kMaxValidSize);
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}
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@end
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