Bug #71384 [Com]: fread() does not detect file access error

Edit report at https://bugs.php.net/bug.php?id=71384&edit=1 ID: 71384 Comment by: salsi at icosaedro dot it Reported by: salsi at icosaedro dot it Summary: fread() does not detect file access error Status: Open Type: Bug Package: Streams related Operating System: Slackware 14.1 PHP Version: master-Git-2016-01-15 (Git) Block user comment: N Private report: N New Comment: 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 */ $s = <<< EOT H4sICI1YmlYAA2RhbWFnZWQtZGlzawDt3TloFGEYgOF/NyvRGE3UeN/3EY3xvo23hSCIkEYb JUaEEBG1EcF4tRZ29iJiL4iVpa0gdhaCraSx0Cp+k0l01aBIjCvM88CbbJJZ9h+Yb7IzzaYE FFVz1BWNi+ZFlahUvcGivOahH2e9e9BZTgMDJ/tLg9tdf/Ogc3jT4edNjPqi7VF56PeXbs2+ 9urJ8fdP77TdPz+l/e6Y7dAv3DvV9+j25mNLn/c3djx7/KE3W1fj0N+q9+NvKv1+E6iZupTP fD7/lcF5BYphYMiNePxpACiUplovAKiV4fcB2fXvcP/y/ceH/WnwAmTH2x9fv+67a5H6f7ko CqPvZnxpr1R+Pv5Lo74Wbhnt4hhzL7LzT/tI579ymlW13fhoQtSQ8vub2X3DSdHkqCnl90en RFOjaX/w+g+z4+/lSOe/Uuqu2m56NCOaGWXrmh3Nieam/L7t/GhBtDDlt2wXVz332rHTn/9g SRRIdo5rTKVy29fH5XJbW36Mt6SGcs/Fy1dauy9e7e3Kj/nXdfWls2e6ui/0nKvpuoHRy/+X fZv/j3X5/AMFUan1AoCaMf9QXOYfisv8Q3GZfygu8w/FZf6huMw/FJf5h+Iy/1Bc5h8AAAAA AAAAAAAAAAAA/itLoqUnUloW35dHK6KV0apodbQmao3WRuui7KNB1qfBj8xKG6KN0aZoc7Ql 2hpti7ZHO6Kd0a5od7Qn2ht1RPui7KO3DkQHo0PR4ehIdHRM9xgAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAKDYvgAo nTthAJABAA== EOT; file_put_contents("damaged-disk.img", gzdecode(base64_decode($s))); ?> Previous Comments: ------------------------------------------------------------------------ [2016-01-16 13:20:07] 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.) ------------------------------------------------------------------------ [2016-01-15 23:23:19] 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 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=71384&edit=1