[Bug linuxthreads/3318] New: Overriding free which clobbers data and calls pthread_getspecific can get bad value (linuxthreads)

[Bug linuxthreads/3318] New: Overriding free which clobbers data and calls pthread_getspecific can get bad value (linuxthreads)

[ian at airs dot com]

This is the linuxthreads version of bugzilla PR 3317, which I reported for NPTL.

If I override the libc free() function, and change that function to clobber some
bytes of the data, and then call pthread_getspecific from that function,
pthread_getspecific can return bad data.  This is because
__pthread_destroy_specifics frees memory before clearing the pointer to it. 
This happens around line 200:

    if (THREAD_GETMEM_NC(self, p_specific[i]) != NULL) {
      free(THREAD_GETMEM_NC(self, p_specific[i]));
      THREAD_SETMEM_NC(self, p_specific[i], NULL);
    }

This should be rewritten to call THREAD_GETMEM_NC, then THREAD_SETMEM_NC, then free.

I will attach a test case which shows the problem on i686-pc-linux-gnu using
Fedora Core 4 with glibc-2.3.6-3 when setting the environment variable
LD_ASSUME_KERNEL to 2.4.19.

-- 
           Summary: Overriding free which clobbers data and calls
                    pthread_getspecific can get bad value (linuxthreads)
           Product: glibc
           Version: 2.3.6
            Status: NEW
          Severity: normal
          Priority: P2
         Component: linuxthreads
        AssignedTo: drow at false dot org
        ReportedBy: ian at airs dot com
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=3318

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[Bug linuxthreads/3318] Overriding free which clobbers data and calls pthread_getspecific can get bad value (linuxthreads)

[ian at airs dot com]

------- Additional Comments From ian at airs dot com  2006-10-07 01:56 -------
Created an attachment (id=1357)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=1357&action=view)
Test case

This test case crashes for me on i686-pc-linux-gnu running Fedora Core 4 with
glibc-2.3.6-3 when I set the environment variable LD_ASSUME_KERNEL to 2.4.19. 
In the __libc_free routine, pthread_getspecific returns garbage.

This isn't the simplest possible test case--it's a modification of the NPTL
test case.  The call to abort winds up hanging as the pthread code waits for a
lock, so I put in an alarm to get the program to actually exit.  The hang is
probably due to the bug I reported in bugzilla PR 2948, which has been fixed in
the mainline sources.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=3318

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[Bug linuxthreads/3318] Overriding free which clobbers data and calls pthread_getspecific can get bad value (linuxthreads)

[drow at sources dot redhat dot com]

------- Additional Comments From drow at sources dot redhat dot com  2006-10-31 15:31 -------
Sorry, but I don't think there's any point in diverging from NPTL on this point;
LinuxThreads is strictly end of life now.  It's reasonably easy to work around
this bug and in fact I'm not sure how you ever encountered it; the sequence
number is first, and if you clobber that, pthread_getspecific will return NULL.

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


http://sourceware.org/bugzilla/show_bug.cgi?id=3318

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[Bug linuxthreads/3318] Overriding free which clobbers data and calls pthread_getspecific can get bad value (linuxthreads)

[drow at sources dot redhat dot com]

------- Additional Comments From drow at sources dot redhat dot com  2006-10-31 21:49 -------
After talking to Ian...

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|WONTFIX                     |


http://sourceware.org/bugzilla/show_bug.cgi?id=3318

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[Bug linuxthreads/3318] Overriding free which clobbers data and calls pthread_getspecific can get bad value (linuxthreads)

[drow at sources dot redhat dot com]

------- Additional Comments From drow at sources dot redhat dot com  2006-10-31 21:50 -------
... I checked in a fix for this, in case LinuxThreads ever builds again.

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


http://sourceware.org/bugzilla/show_bug.cgi?id=3318

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