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[Session] Truncate session file after successful write #23653

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[Session] Truncate session file after successful write #23653

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5 changes: 5 additions & 0 deletions NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,11 @@ PHP NEWS
registrations are freed while still reachable from the cycle collector.
(Ilia Alshanetsky)

- Session:
. Fixed session data loss in the files save handler when writing the session
file fails after it was already truncated. (Ilia Alshanetsky)



24 Sep 2026, PHP 8.4.26

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9 changes: 4 additions & 5 deletions ext/session/mod_files.c
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Expand Up @@ -236,11 +236,6 @@ static zend_result ps_files_write(ps_files *data, zend_string *key, zend_string
return FAILURE;
}

/* Truncate file if the amount of new data is smaller than the existing data set. */
if (ZSTR_LEN(val) < data->st_size) {
php_ignore_value(ftruncate(data->fd, 0));
}

#ifdef HAVE_PWRITE
n = pwrite(data->fd, ZSTR_VAL(val), ZSTR_LEN(val), 0);
#else
Expand Down Expand Up @@ -274,6 +269,10 @@ static zend_result ps_files_write(ps_files *data, zend_string *key, zend_string
return FAILURE;
}

if (ZSTR_LEN(val) < data->st_size) {
php_ignore_value(ftruncate(data->fd, ZSTR_LEN(val)));
}

return SUCCESS;
}

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60 changes: 60 additions & 0 deletions ext/session/tests/session_write_failure_keeps_data.phpt
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@@ -0,0 +1,60 @@
--TEST--
Session files handler must not truncate session file when write fails
--EXTENSIONS--
session
posix
pcntl
--INI--
error_reporting=E_ALL
display_errors=1
session.use_strict_mode=0
--FILE--
<?php
$dir = sys_get_temp_dir() . '/aph_er5_' . getmypid();
if (!is_dir($dir)) {
mkdir($dir);
}
foreach (glob($dir . '/sess_*') as $f) {
unlink($f);
}
ini_set('session.save_path', $dir);

$sid = 'apher5sessid12345678901234567890';
$file = $dir . '/sess_' . $sid;

ob_start();

session_id($sid);
session_start();
$_SESSION['data'] = str_repeat('A', 8192);
session_write_close();

clearstatcache(true);
$before = filesize($file);
var_dump($before > 4096);

pcntl_signal(SIGXFSZ, SIG_IGN);
var_dump(posix_setrlimit(POSIX_RLIMIT_FSIZE, 16, POSIX_RLIMIT_INFINITY));

session_start();
$_SESSION['data'] = str_repeat('B', 4096);
@session_write_close();

clearstatcache(true);
$after = filesize($file);
var_dump($after);
var_dump($after === $before);

ob_end_flush();

foreach (glob($dir . '/sess_*') as $f) {
@unlink($f);
}
@rmdir($dir);
Comment on lines +50 to +53

@NickSdot NickSdot Sep 11, 2026

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Add --CLEAN-- and remove the defensive cleanup at the beginning?

echo "done\n";
--EXPECT--
bool(true)
bool(true)
int(8207)
bool(true)
done
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