[Bug 1767097] [NEW] ftok() returns different result for same (path, id) pair if the inode of the file is changed

[Mattias Säteri]

Public bug reported:

Release: Ubuntu 16.04.2 LTS

Package: libc6:
  Installed: 2.23-0ubuntu7

The ftok man page states that: "The resulting value is the same for all
pathnames that name the same file, when the same value of proj_id is
used".

However, if you call ftok() twice with the same path and id, and the
file has been deleted and created again in between (and the inode of the
file has been changed by this operation, which it will if other files
were created in between), then the result of ftok() will not be the
same.

The following program can be used to reproduce the issue:

#include <sys/types.h>
#include <sys/ipc.h>
#include <stdio.h>
#include <unistd.h>

int main(int argc, char **argv)
{
    int id = 121;
    
    if (argc != 2) {
        printf("Usage: ft <file>\n");
        return 1;
    }

    if (access(argv[1], F_OK) < 0) {
        printf("Failed to access file\n");
        return 1;
    }

    printf("ftok %s %d: 0x%x\n", argv[1], id, ftok(argv[1], (char)id));
    return 0;
}


Compile it into a binary named 'ft', then do the following:

$ touch foo
$ ./ft foo
ftok foo 121: 0x790225bd
$ rm foo
$ touch bar
$ touch foo
$ ftok foo
ftok foo 121: 0x790226ea

The result is not the same although the path and id are the same, which
is not what should happen according to the man page.

** Affects: glibc (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1767097

Title:
  ftok() returns different result for same (path, id) pair if the inode
  of the file is changed

Status in glibc package in Ubuntu:
  New

Bug description:
  Release: Ubuntu 16.04.2 LTS

  Package: libc6:
    Installed: 2.23-0ubuntu7

  The ftok man page states that: "The resulting value is the same for
  all pathnames that name the same file, when the same value of proj_id
  is used".

  However, if you call ftok() twice with the same path and id, and the
  file has been deleted and created again in between (and the inode of
  the file has been changed by this operation, which it will if other
  files were created in between), then the result of ftok() will not be
  the same.

  The following program can be used to reproduce the issue:

  #include <sys/types.h>
  #include <sys/ipc.h>
  #include <stdio.h>
  #include <unistd.h>

  int main(int argc, char **argv)
  {
      int id = 121;
      
      if (argc != 2) {
          printf("Usage: ft <file>\n");
          return 1;
      }

      if (access(argv[1], F_OK) < 0) {
          printf("Failed to access file\n");
          return 1;
      }

      printf("ftok %s %d: 0x%x\n", argv[1], id, ftok(argv[1], (char)id));
      return 0;
  }

  
  Compile it into a binary named 'ft', then do the following:

  $ touch foo
  $ ./ft foo
  ftok foo 121: 0x790225bd
  $ rm foo
  $ touch bar
  $ touch foo
  $ ftok foo
  ftok foo 121: 0x790226ea

  The result is not the same although the path and id are the same,
  which is not what should happen according to the man page.

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