php.net |  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login
Bug #71384 fread() does not detect file access error
Submitted: 2016-01-15 23:23 UTC Modified: -
From: salsi at icosaedro dot it Assigned:
Status: Open Package: Streams related
PHP Version: master-Git-2016-01-15 (Git) OS: Slackware 14.1
Private report: No CVE-ID:
Have you experienced this issue?
Rate the importance of this bug to you:

 [2016-01-15 23:23 UTC] salsi at icosaedro dot it
Description:
------------
Possibly related: bug #71263 fread() does not detects decoding errors from filter bzip2.decompressed (https://bugs.php.net/bug.php?id=71263).

Trying to read an unreadable file, fread() does not to detect the problem and simply returns the empty string; no error nor exception whatsover.

The simplest way to simulate an unreadable file on Linux is to read /proc/self/mem, a file that can be succesfully openend but cannot be read from the very beginning (credits for this trick: http://unix.stackexchange.com/a/6302):

	$ cat /proc/self/mem
	cat: /proc/self/mem: Input/output error

A simple test made with gcc C confirms that fopen() succeeds while fread() gives input/output error.

Under PHP, instead, no errors are detected, and fread() simply returns the empty string, as the following test script proves:


Test script:
---------------
<?php
echo "PHP version: ", PHP_VERSION, "\n";
// set safe test environment:
error_reporting(-1);
ini_set("track_errors", "1");

// maps errors to ErrorException:
function my_error_handler($errno, $message) {
	throw new ErrorException($message);
}
set_error_handler("my_error_handler");

$f = fopen("/proc/self/mem", "r");
do {
	$bytes = fread($f, 1000);
	echo "bytes=";
	var_dump($bytes);
} while (!feof($f));
fclose($f);
// --> bytes=string(0) "", no error whatsoever

echo "Just testing if error detection is still on:\n";
$f = fopen("this file does not exist!", "rb");
?>

Expected result:
----------------
PHP version: 7.1.0-dev
(exception on the first fread() telling the file is unreadable)

Actual result:
--------------
PHP version: 7.1.0-dev
bytes=string(0) ""
Just testing if error detection is still on:
PHP Fatal error:  Uncaught ErrorException: fopen(this file does not exist!): failed to open stream: No such file or directory in /home/salsi/src/phplint/bug-fread-unreadable-file.php:9
Stack trace:
#0 [internal function]: my_error_handler(2, 'fopen(this file...', '/home/salsi/src...', 23, Array)
#1 /home/salsi/src/phplint/bug-fread-unreadable-file.php(23): fopen('this file does ...', 'rb')
#2 {main}
  thrown in /home/salsi/src/phplint/bug-fread-unreadable-file.php on line 9
Fatal error: Uncaught ErrorException: fopen(this file does not exist!): failed to open stream: No such file or directory in /home/salsi/src/phplint/bug-fread-unreadable-file.php:9
Stack trace:
#0 [internal function]: my_error_handler(2, 'fopen(this file...', '/home/salsi/src...', 23, Array)
#1 /home/salsi/src/phplint/bug-fread-unreadable-file.php(23): fopen('this file does ...', 'rb')
#2 {main}
  thrown in /home/salsi/src/phplint/bug-fread-unreadable-file.php on line 9


Patches

Add a Patch

Pull Requests

Add a Pull Request

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2016-01-16 13:20 UTC] danack@php.net
To increase the likelihood of this being fixed, would it be possible for you to attach the C code that you tested with, to show the exact error conditions.

(I'm not saying that will guarantee that it will be fixed, it just makes it a bit more likely.)
 [2016-01-16 15:14 UTC] salsi at icosaedro dot it
Two sources I used to investigate this issue:

- C test program, compiled with gcc under Slackware 14.1 that show how i/o error is detected reading /proc/self/mem.

- PHP program that generates an ext2 disk image corrupted on pourpose on which i/o error might be tested on, as a further example.


// https://bugs.php.net/bug.php?id=71384

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>

int unbuffered() {
	int fd, n;
	char buf[10000];
	
	fd = open("/proc/self/mem", O_RDONLY);
//	fd = open(__FILE__, O_RDONLY);
	if(fd < 0){
		fprintf(stderr, "open(): %s\n", strerror(errno));
		return EXIT_FAILURE;
	}
	
	n = read(fd, buf, 100);
	printf("read(): %d\n", n);
	if(n < 0){
		fprintf(stderr, "read(): %s\n", strerror(errno));
		return EXIT_FAILURE;
	}

	return (EXIT_SUCCESS);
}


int buffered() {
	FILE * f;
	int n;
	char buf[100];
	
	f = fopen("/proc/self/mem", "r");
//	f = fopen(__FILE__, "r");
	if(f == NULL){
		fprintf(stderr, "fopen(): %s\n", strerror(errno));
		return EXIT_FAILURE;
	}
	
	while(1){
		n = fread(buf, 1, 100, f);
		printf("fread(): %d\n", n);
		if(n <= 0){
			if( ferror(f) == 0 ){
				return EXIT_SUCCESS;
			} else {
				fprintf(stderr, "fread(): %s\n", strerror(errno));
				return EXIT_FAILURE;
			}
		}
	}

	return EXIT_SUCCESS;
}


int main(int argc, char** argv) {
	
//	return unbuffered();
	// Output:
	// read(): -1
	// read(): Input/output error

	
	return buffered();
	// Output:
	// fread(): 0
	// fread() : Input / output error

}



<?php

/**
 * damaged-disk.php
 * 
 * Investigating https://bugs.php.net/bug.php?id=71384
 * 
 * This program creates the file "damaged-disk.img" containing the damaged
 * disk image of a Linux ext2 partition; the partition contains a single
 * file named "badfile" that can read only partially before I/O error:
 * 
 * $ su
 * # mkdir baddisk
 * # mount -r damaged-disk.img baddisk
 * # cat baddisk/badfile
 * cat: baddisk/badfile: Input/output error
 */

$s = <<< EOT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EOT;

file_put_contents("damaged-disk.img", gzdecode(base64_decode($s)));
?>
 
PHP Copyright © 2001-2017 The PHP Group
All rights reserved.
Last updated: Tue Aug 29 15:01:52 2017 UTC