Re: Linux, too, sot of (Windows MS-DOS Device Name DoS vulnerabilities)

From: Glynn Clements (glynn.clementsat_private)
Date: Wed Jul 18 2001 - 12:58:43 PDT

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    alandat_private wrote:
    
    > > One may be tempted to block all the files below /dev inside
    > > the browser/servers.
    > > Could this be a cure for this problem under linux/UNIX?
    > 
    >   No.  The browsers should be using the 'fstat' function, prior to
    > opening any 'file://' URL.
    
    fstat() requires a descriptor; you need to use stat().
    
    BTW, on Unix, simply open()ing a device can have undesirable
    consequences, hence the need to use stat() before opening the file.
    
    > Regular files and directories should be
    > OK.  Links should have their links de-referenced, and the linked-to
    > file 'fstat'ed also.  Any other files should be ignored.
    
    Symbolic links don't show up in the results from stat() or fstat();
    you would need to use lstat() if you wanted to identify links (in this
    case, you don't).
    
    I notice that the Windows mechanism which is being recommended, i.e.
    GetFileType(), requires a file handle. As Alun Jones pointed out:
    
    > The person quoted here doesn't indicate whether it is merely opening the 
    > device files, or trying to access (read or write) their contents, is what 
    > will "wedge the DOS box" - if the former, then GetFileType is sadly of no 
    > assistance.
    
    Can anyone shed any light upon whether the act of opening a device
    under Windows can have undesirable side effects?
    -- 
    Glynn Clements <glynn.clementsat_private>
    



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