[Bug libc/11161] New: process with closed fd 2 sees no problem on stdout

[Bug libc/11161] New: process with closed fd 2 sees no problem on stdout

[kogorman at calpoly dot edu]

When a process is started with file descriptor 2 closed (such as some daemon
processes, or for headless operation), or if fd 2 becomes closed without
explicitly closing stdout, functions on filestream stdout do not report errors.
 I will attach a C program that illustrates this situation.
Run it from bash as "fsbad >&-" to start with a closed STDOUT_FILENO.

I know that processes which expect fd2 to be closed should not be writing to
stdout, but it seems odd for the error not to be reported.  What is even more
odd is that the first attempt to use stdout changes 'errno' to EBADF, but
otherwise gives a normal return.

This was a problem for me because I am teaching systems programming, and I tell
my students to get in the habit of checking all calls for errors, and they hit
on this as a technique to test their code, and thoght they had done something wrong.

-- 
           Summary: process with closed fd 2 sees no problem on stdout
           Product: glibc
           Version: 2.8
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: kogorman at calpoly dot edu
                CC: glibc-bugs at sources dot redhat dot com,kogorman at
                    calpoly dot edu


http://sourceware.org/bugzilla/show_bug.cgi?id=11161

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[Bug libc/11161] process with closed fd 2 sees no problem on stdout

[kogorman at calpoly dot edu]

------- Additional Comments From kogorman at calpoly dot edu  2010-01-12 19:46 -------
Created an attachment (id=4508)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=4508&action=view)
C program to Illustrate the anomaly if started with file descriptor 2 closed


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http://sourceware.org/bugzilla/show_bug.cgi?id=11161

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[Bug libc/11161] process with closed fd 2 sees no problem on stdout

[kogorman at calpoly dot edu]

------- Additional Comments From kogorman at calpoly dot edu  2010-01-12 19:52 -------
Oops, that should be "fd 1".  I hate typos in the title.

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http://sourceware.org/bugzilla/show_bug.cgi?id=11161

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[Bug libc/11161] process with closed fd 2 sees no problem on stdout

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2010-01-15 07:59 -------
The behavior is as expected.  There are situations where this is exactly what
you want.  We are even reassigning the unopened descriptors to /dev/null in
security critical apps.

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


http://sourceware.org/bugzilla/show_bug.cgi?id=11161

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[Bug libc/11161] process with closed fd 2 sees no problem on stdout

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=11161

Florian Weimer <fweimer at redhat dot com> changed:

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

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