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AltahrimAltahrim
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feat(previews): add file signature check before opening files
Signed-off-by: Benjamin Gaussorgues <benjamin.gaussorgues@nextcloud.com>
1 parent 7887665 commit 640d15b

10 files changed

Lines changed: 191 additions & 5 deletions

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‎lib/private/Preview/Bitmap.php‎

Lines changed: 49 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -38,6 +38,25 @@
3838
*/
3939
abstract class Bitmap extends ProviderV2 {
4040

41+
/**
42+
* List of MIME types that this preview provider is allowed to process.
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*
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* These should correspond to the MIME types *identified* by Imagemagick
45+
* for files to be processed by this provider. These do / will not
46+
* necessarily need to match the MIME types stored in the database
47+
* (which are identified by IMimeTypeDetector).
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*
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* @return string Regular expression
50+
*/
51+
abstract protected function getAllowedMimeTypes(): string;
52+
53+
/**
54+
* @return list<string>
55+
*/
56+
abstract protected function getMagicStrings(): array;
57+
58+
abstract protected function getImagickFormatHint(): string;
59+
4160
/**
4261
* {@inheritDoc}
4362
*/
@@ -87,12 +106,25 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
87106
* @param int $maxY
88107
*
89108
* @return \Imagick
109+
*
110+
* @throws \Exception
90111
*/
91112
private function getResizedPreview($tmpPath, $maxX, $maxY) {
92113
$bp = new Imagick();
93114

115+
if (!$this->isMagicStringSupported($tmpPath)) {
116+
throw new \Exception('Invalid image type: magic string not recognized');
117+
}
118+
119+
// Validate mime type
120+
$bp->pingImage($this->getImagickFormatHint() . ':' . $tmpPath . '[0]');
121+
$mimeType = $bp->getImageMimeType();
122+
if (!preg_match($this->getAllowedMimeTypes(), $mimeType)) {
123+
throw new \Exception('File mime type does not match the preview provider: ' . $mimeType);
124+
}
125+
94126
// Layer 0 contains either the bitmap or a flat representation of all vector layers
95-
$bp->readImage($tmpPath . '[0]');
127+
$bp->readImage($this->getImagickFormatHint() . ':' . $tmpPath . '[0]');
96128

97129
$bp = $this->resize($bp, $maxX, $maxY);
98130

@@ -101,6 +133,22 @@ private function getResizedPreview($tmpPath, $maxX, $maxY) {
101133
return $bp;
102134
}
103135

136+
private function isMagicStringSupported(string $filepath): bool {
137+
$signatures = $this->getMagicStrings();
138+
if (empty($signatures)) {
139+
return true;
140+
}
141+
$length = array_reduce($signatures, static fn (int $carry, string $signature) => max($carry, strlen($signature)), 0);
142+
$firstBytes = file_get_contents($filepath, false, null, 0, $length);
143+
foreach ($signatures as $signature) {
144+
if (str_starts_with($firstBytes, $signature)) {
145+
return true;
146+
}
147+
}
148+
149+
return false;
150+
}
151+
104152
/**
105153
* Returns a resized \Imagick object
106154
*

‎lib/private/Preview/Font.php‎

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -30,4 +30,22 @@ class Font extends Bitmap {
3030
public function getMimeType(): string {
3131
return '/application\/(?:font-sfnt|x-font$)/';
3232
}
33+
34+
/**
35+
* {@inheritDoc}
36+
*/
37+
protected function getAllowedMimeTypes(): string {
38+
return '/(application|image)\/(?:font-sfnt|x-font|x-otf|x-ttf|x-pfb$)/';
39+
}
40+
41+
protected function getMagicStrings(): array {
42+
return [
43+
"\x00\x01\x00\x00\x00", // TTF
44+
'OTTO', // OTF
45+
];
46+
}
47+
48+
protected function getImagickFormatHint(): string {
49+
return 'ttf';
50+
}
3351
}

‎lib/private/Preview/HEIC.php‎

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -44,7 +44,7 @@ class HEIC extends ProviderV2 {
4444
* {@inheritDoc}
4545
*/
4646
public function getMimeType(): string {
47-
return '/image\/hei(f|c)/';
47+
return '/image\/(x-)?hei(f|c)/';
4848
}
4949

5050
/**
@@ -108,12 +108,22 @@ public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
108108
* @param int $maxY
109109
*
110110
* @return \Imagick
111+
*
112+
* @throws \Exception
111113
*/
112114
private function getResizedPreview($tmpPath, $maxX, $maxY) {
113115
$bp = new \Imagick();
114116

117+
// Some HEIC files just contain (or at least are identified as) other formats
118+
// like JPEG. We just need to check if the image is safe to process.
119+
$bp->pingImage('heic:' . $tmpPath . '[0]');
120+
$mimeType = $bp->getImageMimeType();
121+
if (!preg_match('/^image\/(x-)?(png|jpeg|gif|bmp|tiff|webp|hei(f|c)|avif)$/', $mimeType)) {
122+
throw new \Exception('File mime type does not match the preview provider: ' . $mimeType);
123+
}
124+
115125
// Layer 0 contains either the bitmap or a flat representation of all vector layers
116-
$bp->readImage($tmpPath . '[0]');
126+
$bp->readImage('heic:' . $tmpPath . '[0]');
117127

118128
// Fix orientation from EXIF
119129
$bp->autoOrient();

‎lib/private/Preview/Illustrator.php‎

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,4 +31,19 @@ class Illustrator extends Bitmap {
3131
public function getMimeType(): string {
3232
return '/application\/illustrator/';
3333
}
34+
35+
/**
36+
* {@inheritDoc}
37+
*/
38+
protected function getAllowedMimeTypes(): string {
39+
return '/application\/(illustrator|pdf)/';
40+
}
41+
42+
protected function getMagicStrings(): array {
43+
return ["\x25\x50\x44\x46"];
44+
}
45+
46+
protected function getImagickFormatHint(): string {
47+
return 'ai';
48+
}
3449
}

‎lib/private/Preview/PDF.php‎

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,4 +31,19 @@ class PDF extends Bitmap {
3131
public function getMimeType(): string {
3232
return '/application\/pdf/';
3333
}
34+
35+
/**
36+
* {@inheritDoc}
37+
*/
38+
protected function getAllowedMimeTypes(): string {
39+
return '/application\/pdf/';
40+
}
41+
42+
protected function getMagicStrings(): array {
43+
return ['%PDF-'];
44+
}
45+
46+
protected function getImagickFormatHint(): string {
47+
return 'pdf';
48+
}
3449
}

‎lib/private/Preview/Photoshop.php‎

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,4 +31,19 @@ class Photoshop extends Bitmap {
3131
public function getMimeType(): string {
3232
return '/application\/x-photoshop/';
3333
}
34+
35+
/**
36+
* {@inheritDoc}
37+
*/
38+
protected function getAllowedMimeTypes(): string {
39+
return '/(application|image)\/(x-photoshop|x-psd)/';
40+
}
41+
42+
protected function getMagicStrings(): array {
43+
return ['8BPS'];
44+
}
45+
46+
protected function getImagickFormatHint(): string {
47+
return 'psd';
48+
}
3449
}

‎lib/private/Preview/Postscript.php‎

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,4 +31,19 @@ class Postscript extends Bitmap {
3131
public function getMimeType(): string {
3232
return '/application\/postscript/';
3333
}
34+
35+
/**
36+
* {@inheritDoc}
37+
*/
38+
protected function getAllowedMimeTypes(): string {
39+
return '/application\/postscript/';
40+
}
41+
42+
protected function getMagicStrings(): array {
43+
return ['%!PS'];
44+
}
45+
46+
protected function getImagickFormatHint(): string {
47+
return 'ps';
48+
}
3449
}

‎lib/private/Preview/SGI.php‎

Lines changed: 16 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,21 @@ class SGI extends Bitmap {
2828
* {@inheritDoc}
2929
*/
3030
public function getMimeType(): string {
31-
return '/image\/sgi/';
31+
return '/image\/(x-)?sgi/';
32+
}
33+
34+
/**
35+
* {@inheritDoc}
36+
*/
37+
protected function getAllowedMimeTypes(): string {
38+
return '/image\/(x-)?sgi/';
39+
}
40+
41+
protected function getMagicStrings(): array {
42+
return ["\x01\xDA"];
43+
}
44+
45+
protected function getImagickFormatHint(): string {
46+
return 'sgi';
3247
}
3348
}

‎lib/private/Preview/TGA.php‎

Lines changed: 16 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,21 @@ class TGA extends Bitmap {
2828
* {@inheritDoc}
2929
*/
3030
public function getMimeType(): string {
31-
return '/image\/t(ar)?ga/';
31+
return '/image\/(x-)?t(ar)?ga/';
32+
}
33+
34+
/**
35+
* {@inheritDoc}
36+
*/
37+
protected function getAllowedMimeTypes(): string {
38+
return '/image\/(x-)?t(ar)?ga/';
39+
}
40+
41+
protected function getMagicStrings(): array {
42+
return [];
43+
}
44+
45+
protected function getImagickFormatHint(): string {
46+
return 'tga';
3247
}
3348
}

‎lib/private/Preview/TIFF.php‎

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,4 +31,24 @@ class TIFF extends Bitmap {
3131
public function getMimeType(): string {
3232
return '/image\/tiff/';
3333
}
34+
35+
/**
36+
* {@inheritDoc}
37+
*/
38+
protected function getAllowedMimeTypes(): string {
39+
return '/image\/tiff/';
40+
}
41+
42+
protected function getMagicStrings(): array {
43+
return [
44+
"II*\x00",
45+
"MM\x00*",
46+
"II+\x00",
47+
"MM\x00+",
48+
];
49+
}
50+
51+
protected function getImagickFormatHint(): string {
52+
return 'tiff';
53+
}
3454
}

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