[Bug libc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[Bug libc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[clausen at econ dot upenn.edu]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Andrew Clausen <clausen at econ dot upenn.edu> changed:

           What    |Removed                     |Added
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             Status|RESOLVED                    |REOPENED
                 CC|                            |clausen at econ dot
                   |                            |upenn.edu
         Resolution|INVALID                     |

--- Comment #3 from Andrew Clausen <clausen at econ dot upenn.edu> 2011-04-16 15:34:58 UTC ---
I agree that this is a real bug.  I want to memset(ptr, 0,
malloc_usable_size(ptr)) my memory on free(3), so that my computer forgets all
of my private information.  This should work with mcheck() and friends.

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[Bug libc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[ppluzhnikov at google dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Paul Pluzhnikov <ppluzhnikov at google dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |ppluzhnikov at google dot
                   |                            |com

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[Bug libc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[aj at suse dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Andreas Jaeger <aj at suse dot de> changed:

           What    |Removed                     |Added
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                 CC|                            |aj at suse dot de
         AssignedTo|gotom at debian dot or.jp   |drepper.fsp at gmail dot
                   |                            |com

--- Comment #4 from Andreas Jaeger <aj at suse dot de> 2012-02-06 14:06:43 UTC ---
Looking at the documentation of malloc_usable_size, I agree this is a bug in
glibc.

IMO for the snippet in the report, usable should be 7 with MALLOC_CHECK_>0.

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[Bug malloc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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          Component|libc                        |malloc

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[Bug malloc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[aj at suse dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Andreas Jaeger <aj at suse dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2012-05-06
         AssignedTo|drepper.fsp at gmail dot    |unassigned at sourceware
                   |com                         |dot org

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[Bug malloc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[siddhesh at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |siddhesh at redhat dot com
         AssignedTo|unassigned at sourceware    |siddhesh at redhat dot com
                   |dot org                     |

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[Bug malloc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[siddhesh at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=1349

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
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             Status|REOPENED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #5 from Siddhesh Poyarekar <siddhesh at redhat dot com> 2012-09-05 16:22:31 UTC ---
Fixed in master: 6ef9cc37f0ea151a54e5c8a19950a6d5b6ff8a96

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[Bug malloc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[jackie.rosen at hushmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=1349

Jackie Rosen <jackie.rosen at hushmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jackie.rosen at hushmail dot com

--- Comment #6 from Jackie Rosen <jackie.rosen at hushmail dot com> ---
*** Bug 260998 has been marked as a duplicate of this bug. ***
Seen from the domain http://volichat.com
Page where seen: http://volichat.com/adult-chat-rooms
Marked for reference. Resolved as fixed @bugzilla.

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[Bug malloc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[schwab at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=1349

Andreas Schwab <schwab at sourceware dot org> changed:

           What    |Removed                     |Added
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                 CC|jackie.rosen at hushmail dot com   |

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[Bug libc/1349] New: malloc_usable_size() incorrect when MALLOC_CHECK_>0

[jkearney at endeca dot com]

When MALLOC_CHECK_>0, an extra byte is added to each allocation for checking. 
malloc_usable_size() doesn't take this extra byte off the return value in this
case.  Try the following with MALLOC_CHECK_=2:

    void* p = malloc(7);
    size_t usable = malloc_usable_size(p);
    memset(p, 0, usable);
    p = realloc(p, 7);

-- 
           Summary: malloc_usable_size() incorrect when MALLOC_CHECK_>0
           Product: glibc
           Version: 2.3.5
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: gotom at debian dot or dot jp
        ReportedBy: jkearney at endeca dot com
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=1349

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[Bug libc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2005-09-28 22:45 -------
You are misusing malloc_usable_size().  The function gives you information on
how much memory a really call can provide you in place.  It does not
automagically extends the memory block.  The realloc call is needed.

Admittedly, the information returned by malloc_usable_size() doesn't take the
magic byte into account and therefore a really call, which would normally be
extended in place, can require a repositioning.  But this is no big issue and
not worth changing.

In summary: your test code is wrong and deserves to crash.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


http://sourceware.org/bugzilla/show_bug.cgi?id=1349

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[Bug libc/1349] malloc_usable_size() incorrect when MALLOC_CHECK_>0

[jkearney at endeca dot com]

------- Additional Comments From jkearney at endeca dot com  2005-09-29 01:22 -------
Subject: RE:  malloc_usable_size() incorrect when MALLOC_CHECK_>0

Ulrich, I'm not sure that we're communicating here.  The comment for malloc_usable_size() says:

  Returns the number of bytes you can actually use in
  an allocated chunk, which may be more than you requested (although
  often not) due to alignment and minimum size constraints.
  You can use this many bytes without worrying about
  overwriting other allocated objects.

The code sample given conforms to this contract, and works fine when MALLOC_CHECK_=0.  When MALLOC_CHECK_ is not 0, the magic byte is overwritten because it is not accounted for.  Therefore, *any* operation that checks the magic bytes after the memset() will report an error and/or abort.  Change realloc() to free() and the same thing will happen.  It has nothing to do with "extension" or "repositioning".

Granted, it's a usage which is not very nice, but I don't think it's "misusing malloc_usable_size()".

-----Original Message-----
From: drepper at redhat dot com
[mailto:sourceware-bugzilla@sourceware.org]
Sent: Wednesday, September 28, 2005 6:46 PM
To: Jim Kearney
Subject: [Bug libc/1349] malloc_usable_size() incorrect when
MALLOC_CHECK_>0



------- Additional Comments From drepper at redhat dot com  2005-09-28 22:45 -------
You are misusing malloc_usable_size().  The function gives you information on
how much memory a really call can provide you in place.  It does not
automagically extends the memory block.  The realloc call is needed.

Admittedly, the information returned by malloc_usable_size() doesn't take the
magic byte into account and therefore a really call, which would normally be
extended in place, can require a repositioning.  But this is no big issue and
not worth changing.

In summary: your test code is wrong and deserves to crash.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


http://sourceware.org/bugzilla/show_bug.cgi?id=1349

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