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.)

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)));
?>

fopen() should have failed in first place, but this check is missing in the php code.

Thanks.

Bug #71384 [Opn]: fread() does not detect file access error
https://bugs.php.net/bug.php?id=71384&edit=2


Maybe it worth to summarize the general issue emerged from an old thread I started back in 2016-01-21 on the developers' mailing list with subject

"Severe safety fail in file access and stream filters"
https://www.mail-archive.com/internals@lists.php.net/msg83033.html

There, several bugs related to the I/O layer are listed involving files, sockets and filtered streams, which are still all open:

+ Missing error verification after fwrite()
https://bugs.php.net/bug.php?id=39598

+ fread() does not detects decoding errors from filter bzip2.decompress
https://bugs.php.net/bug.php?id=71263

+ fread() does not detect file access error
https://bugs.php.net/bug.php?id=71384

+ fread() does not detect decoding errors from filter zlib.inflate
https://bugs.php.net/bug.php?id=71417

+ require* and include* do not detect input/output error
https://bugs.php.net/bug.php?id=71385

...and maybe much more spread here and there among the libraries, possibly including data base connections and more. Yasuo Ohgaki found that the the origin of the issue has a common denominator, that is errors do not propagate from the libc to the PHP streams interface and get lost with unpredictable results:

> Plain file stream reads data by php_stdiop_read()
> http://lxr.php.net/xref/PHP_5_6/main/streams/plain_wrapper.c#338
> As you can see there is no way to return errors from it. We need
> errno like error handling for PHP streams to propagate errors as well
> as more robust code for unexpected.

Julien Pauli tells there is no a simple fix, and the whole streams library should be re-designed from scratch:

> I think what we should do is sit around the table with people
> interested (Daniel Lowrey may be one of them), and plan a full rewrite
> of streams for PHP next major (PHP 8).

This will generate a

fread(): read of 8192 bytes failed with errno=5 Input/output error

notice (promoted to ErrorException in your example) in PHP 7.4.