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Fix OOB gzseek() causing assertion failure #20785

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Fix OOB gzseek() causing assertion failure #20785

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0f5a7d0
Add test with wrong result
ndossche Dec 26, 2025
83f8f24
Fix OOB gzseek() causing assertion failure
ndossche Dec 26, 2025
52fcfd7
make it z_off_t
ndossche Dec 26, 2025
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19 changes: 19 additions & 0 deletions ext/zlib/tests/gzseek_seek_oob.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
--TEST--
Test function gzseek() by seeking out of bounds
--EXTENSIONS--
zlib
--FILE--
<?php
$f = __DIR__."/004.txt.gz";
$h = gzopen($f, 'r');

var_dump(gzseek($h, -100, SEEK_CUR));
var_dump(gzseek($h, 0, SEEK_CUR));
var_dump(gztell($h));

gzclose($h);
?>
--EXPECT--
int(-1)
int(0)
int(0)
9 changes: 7 additions & 2 deletions ext/zlib/zlib_fopen_wrapper.c
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Original file line number Diff line number Diff line change
Expand Up @@ -94,9 +94,14 @@ static int php_gziop_seek(php_stream *stream, zend_off_t offset, int whence, zen
php_error_docref(NULL, E_WARNING, "SEEK_END is not supported");
return -1;
}
*newoffs = gzseek(self->gz_file, offset, whence);

return (*newoffs < 0) ? -1 : 0;
z_off_t new_offset = gzseek(self->gz_file, offset, whence);
if (new_offset < 0) {
return -1;
}

*newoffs = new_offset;
return 0;
}

static int php_gziop_close(php_stream *stream, int close_handle)
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