buffer overflow problems

This is a discussion on buffer overflow problems within the C++ Programming forums, part of the General Programming Boards category; I have a small project to make a simple program that uses SHA-1 to hash a file. I'm using SHA-1 ...

  1. #1
    30 Helens Agree neandrake's Avatar
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    buffer overflow problems

    I have a small project to make a simple program that uses SHA-1 to hash a file. I'm using SHA-1 classes/code from codeproject (http://www.codeproject.com/cpp/csha1.asp) (SHA1.cpp and SHA1.h). All I'm trying to do is show the hash code of any file. I'm getting an error right when the program exits (only if the file exists and it gets hashed)

    Code:
    Error:
    Run-Time Check Failure #2 - Stack around the variable 'lpszHash' was corrupted.
    The code isn't hard to understand, not alot of it either, I would really appreciate the help on this. The error is a Native error and only is reported when using debug mode (I found this out in the help file). How can I fix my program? Obviously I want to practice good programming.

    PS - I changed the code, it used to check for a file specified in parameters to running the program, but I got sick of having to mess with that at the moment, so I specified for it to hash main.obj
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    Environment: OS X, GCC / G++
    Codes: Java, C#, C/C++
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  2. #2
    Registered User Codeplug's Avatar
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    The usage looks find to me. Notice what is "around the variable 'lpszHash'":
    Code:
        CSHA1 shaFile;
        char lpszHash[50];
    Perhaps CSHA1 is corrupting itself and mabye lpszHash as well.
    Use the debugger and see if any bytes within lpszHash change when you call a method of shaFile.

    gg

  3. #3
    and the hat of wrongness Salem's Avatar
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    I guess 50 bytes isn't enough for all those strcat() in void CSHA1::ReportHash(char *szReport, unsigned char uReportType)
    A quick calc suggests at least 60 bytes is needed
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  4. #4
    Registered User Codeplug's Avatar
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    Yeah, don't forget about that space like I did
    Code:
        sprintf(szTemp, " %02X", m_digest[i]);
        //               ^here
    gg

  5. #5
    30 Helens Agree neandrake's Avatar
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    right! doh! you use it too? works fine now, thanks.
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  6. #6
    30 Helens Agree neandrake's Avatar
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    Now that it works, how can I add it to the right-click menu of every file type? Is there some registry key I need to modify? I just want to be able to right click any file and get the hash. Thanks.
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  7. #7
    and the hat of wrongness Salem's Avatar
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    > Now that it works, how can I add it to the right-click menu of every file type?
    If you put a link to your executable in the "Send to" folder, then it should invoke your program with argv[] set to the filename(s) you've selected.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  8. #8
    Registered User Codeplug's Avatar
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    Originally posted by Codeplug
    Yeah, don't forget about that space like I did
    Originally posted by neandrake
    you use it too?
    No. I just did in my head: 20*2=40 is less than 50.
    I figured you did the same thing.

    gg

  9. #9
    Skunkmeister Stoned_Coder's Avatar
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    read on msdn about extending shortcut menus in the windows shell.
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  10. #10
    30 Helens Agree neandrake's Avatar
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    thanks stoner, but, I didn't find anything about adding it for all files. I once found a program (not really a program) that used an INI file (right click, select Install) to register a new command for all files. Any idea how to do something similar, or at least accomplish the same goal?
    Environment: OS X, GCC / G++
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  11. #11
    Cat
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    Here's one way: Put the following as a text file:

    REGEDIT4

    [HKEY_CLASSES_ROOT\*\shell\Open with Notepad\command]
    @="notepad.exe \"%1\""
    and change it to end in .reg.

    Then, you can double-click and it would create those keys for you. Of course, replace "open with notepad" with your program, and "notepad.exe" with the full path to your file. %1 means the filename will be passed as the first parameter to your program. You can specify any other command line params, if you feel like it.

    So, if you wanted to throw some switches in (this example also shows how to handle pathnames that may have spaces, via the quotes, and the need for double \\ just like with strings in C:

    REGEDIT4

    [HKEY_CLASSES_ROOT\*\shell\Use my program\command]
    @="\"C:\\program files\\my program.exe\" -open -shell \"%1\""
    The above string inserted into the registry actually works out to be:
    "C:\program files\my program.exe" -open -shell "%1"
    after the escape characters are handled.

    You can do pretty much the exact same with an .INI, same idea (making a reg key). I forget the INI syntax offhand, though.
    Last edited by Cat; 12-04-2003 at 01:54 AM.
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  12. #12
    Cat without Hat CornedBee's Avatar
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    Here's a complete shell COM object I wrote that adds functionality to all files.

    Adapt it to your needs.
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    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  13. #13
    Skunkmeister Stoned_Coder's Avatar
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    Well I managed to find thisin about 1 second..... Extending shortcut menus
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  14. #14
    Cat without Hat CornedBee's Avatar
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    But it doesn't handle the * file class, which, I believe, is not as simple as the others.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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