[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[ppluzhnikov at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Paul Pluzhnikov <ppluzhnikov at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|fdopen(..., "a"); fwrite(); |fdopen(..., "a"); fwrite();
                   |ftell() sequence gives      |ftello() sequence gives
                   |wrong answer                |wrong answer

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[Bug stdio/16532] New: fdopen(..., "a"); fwrite(); ftell() sequence gives wrong answer

[ppluzhnikov at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

            Bug ID: 16532
           Summary: fdopen(..., "a"); fwrite(); ftell() sequence gives
                    wrong answer
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: stdio
          Assignee: unassigned at sourceware dot org
          Reporter: ppluzhnikov at google dot com

This is a regression from 2.15.

Test case below, does not assert with glibc-2.15, but asserts with current
trunk.

If I use fopen() instead of fdopen() ["./a.out -o"] or if I fflush() after
fwrite() ["./a.out -f"], then assert goes away.

/* --- cut --- */
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
  FILE *fp;
  size_t written;
  off_t off;
  int do_flush = 0, do_fopen = 0;
  int opt;
  const char *const fname = "/tmp/output";

  while ((opt = getopt (argc, argv, "fo")) != -1)
    {
      switch (opt)
        {
        case 'f': do_flush = 1; break;
        case 'o': do_fopen = 1; break;
        }
    }

  fp = fopen (fname, "w");
  written = fwrite ("abcabc", 1, 6, fp);
  assert (written == 6);

  fclose (fp);

  if (do_fopen)
    fp = fopen (fname, "a");
  else
    {
      int fd = open (fname, O_WRONLY, 0);
      assert (fd != -1);
      fp = fdopen (fd, "a");
    }

  assert (fp != NULL);

  written = fwrite ("ghi", 1, 3, fp);
  assert (written == 3);

  if (do_flush)
    fflush (NULL);

  off = ftello (fp);
  assert (off == 9);

  return 0;
}
/* --- cut --- */

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[ppluzhnikov at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Paul Pluzhnikov <ppluzhnikov at google dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |siddhesh at redhat dot com

--- Comment #1 from Paul Pluzhnikov <ppluzhnikov at google dot com> ---
This broke with commit adb26faefe47b7d34c941cbfc193ca7a5fde8e3f:


 2012-09-28  Siddhesh Poyarekar  <siddhesh@redhat.com>

      [BZ #5298]
       * libio/fileops.c (_IO_new_file_seekoff): Don't flush buffer
       for ftell.  Compute offsets from write pointers instead.
       * libio/wfileops.c (_IO_wfile_seekoff): Likewise.

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[siddhesh at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |siddhesh at redhat dot com

--- Comment #2 from Siddhesh Poyarekar <siddhesh at redhat dot com> ---
Thanks, I'll look into it.

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[siddhesh at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[siddhesh at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugdal at aerifal dot cx

--- Comment #3 from Siddhesh Poyarekar <siddhesh at redhat dot com> ---
*** Bug 16605 has been marked as a duplicate of this bug. ***

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[siddhesh at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Siddhesh Poyarekar <siddhesh at redhat dot com> ---
Fixed in master:

commit 000232b9bcbf194f1e5fd0ff380000f341505405
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Tue Mar 4 07:45:58 2014 +0530

    Separate ftell from fseek logic and avoid modifying FILE data (#16532)

    ftell semantics are distinct from fseek(SEEK_CUR) especially when it
    is called on a file handler that is not yet active.  Due to this
    caveat, much care needs to be taken while modifying the handler data
    and hence, this first iteration on separating out ftell focusses on
    maintaining handler data integrity at all times while it figures out
    the current stream offset.  The result is that it makes a syscall for
    every offset request.

    There is scope for optimizing this by caching offsets when we know
    that the handler is active.  A simple way to find out is when the
    buffers have data.  It is not so simple to find this out when the
    buffer is empty without adding some kind of flag.

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug stdio/16532] fdopen(..., "a"); fwrite(); ftello() sequence gives wrong answer

[tim.lammens at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16532

Tim <tim.lammens at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tim.lammens at gmail dot com

--- Comment #5 from Tim <tim.lammens at gmail dot com> ---
I am afraid the provided fix has caused a memory leak.
See https://sourceware.org/bugzilla/show_bug.cgi?id=17370.
The malloc in the patch has not been freed.

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