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fix #78326 memory issues with stream_get_contents() fixed length buffer #4464

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fix #78326 memory issues with stream_get_contents() fixed length buffer #4464

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18 changes: 18 additions & 0 deletions ext/standard/tests/streams/bug78326.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
--TEST--
memory allocation on stream_get_contents()
--INI--
memory_limit=32M
--FILE--
<?php
$f = tmpfile();
fwrite($f, '.');

$chunks = array();
for ($i = 0; $i < 1000; ++$i) {
rewind($f);
$chunks[] = stream_get_contents($f, 1000000);
}
var_dump(count($chunks));
?>
--EXPECT--
int(1000)
10 changes: 10 additions & 0 deletions ext/standard/tests/streams/bug78326_1.phpt
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@@ -0,0 +1,10 @@
--TEST--
proper string length on stream_get_contents()
--FILE--
<?php
$f = fopen('php://memory', 'rw');
fwrite($f, str_repeat('X', 1000));
fseek($f, 0);
var_dump(strlen(stream_get_contents($f, 1024)));
--EXPECT--
int(1000)
7 changes: 6 additions & 1 deletion main/streams/streams.c
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Expand Up @@ -1418,8 +1418,13 @@ PHPAPI zend_string *_php_stream_copy_to_mem(php_stream *src, size_t maxlen, int
ptr += ret;
}
if (len) {
*ptr = '\0';
ZSTR_LEN(result) = len;
ZSTR_VAL(result)[len] = '\0';
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@nikic nikic Jul 23, 2019

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You might want to use the same logic as in https://github.com/php/php-src/blob/master/main/streams/streams.c#L759 and only truncate if the "wastage" is large enough.

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@acasademont acasademont Jul 23, 2019

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@nikic thanks! I guess that the potential savings of the truncate are not worth the extra performance costs of the function and memory copy calls if the "waste" is not large enough?

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@acasademont acasademont Jul 23, 2019

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done!

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@nikic nikic Jul 24, 2019

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This dropped the ZSTR_LEN(result) = len assignment, which is still needed in case we don't truncate. I'm surprised this doesn't cause test failures.

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@acasademont acasademont Jul 24, 2019

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@nikic you're right, it didn't I'm afraid, any ideas for a test that maybe we could add?

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@acasademont acasademont Jul 24, 2019

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fixed in any case

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@nikic nikic Jul 24, 2019

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<?php
$f = fopen('php://memory', 'rw');
fwrite($f, str_repeat('X', 1000));
fseek($f, 0); 
var_dump(strlen(stream_get_contents($f, 1024)));

should show the issue.

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@acasademont acasademont Jul 24, 2019

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@nikic it did, thanks! I added the additional test just to be on the safe side


/* Only truncate if the savings are large enough */
if (len < maxlen / 2) {
result = zend_string_truncate(result, len, persistent);
}
} else {
zend_string_free(result);
result = NULL;
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