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Fuzz exif thumbnail handling - #24722
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exif_read_data() only reads the thumbnail if $read_thumbnail is true, and exif_thumbnail() only scans the thumbnail for its dimensions if they are requested, so the exif fuzzer never reached this code.
ndossche
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Oct 26, 2026
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I agree with this, see my (minor) suggestion please
| @@ -47,7 +47,23 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { | |||
| php_stream_write(stream, (const char *) Data, Size); | |||
| php_stream_to_zval(stream, &stream_zv); | |||
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One small cleanup you can do:
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| php_stream_to_zval(stream, &stream_zv); | |
| php_stream_to_zval(stream, &args[0]); |
And then get rid of stream_zv, and the ZVAL_COPY_VALUE(&args[0], &stream_zv); below
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Thanks, done.
ndossche
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Oct 27, 2026
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Merged, thank you for your contribution! |
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php-fuzz-exifcallsexif_read_data($stream)with the default arguments. With$read_thumbnail = false, the thumbnail is never extracted (ImageInfo->read_thumbnailgates several code paths inext/exif/exif.c), andexif_thumbnail()is not called at all.The fuzzer now calls
exif_read_data($stream, null, false, true)andexif_thumbnail($stream, $width, $height, $type). Passing$width/$heightmakesexif_thumbnail()callexif_scan_thumbnail().Replaying the checked-in
sapi/fuzzer/corpus/exif(no fuzzing):zif_exif_thumbnailexif_thumbnail_buildexif_thumbnail_extractexif_thumbnail_in_fileexif_scan_thumbnailThe input format is unchanged, existing corpora stay valid.