[Bug dynamic-link/15022] New: Global-scope dlopen issues in static executables

["macro at linux-mips dot org" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15022

             Bug #: 15022
           Summary: Global-scope dlopen issues in static executables
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
        AssignedTo: unassigned@sourceware.org
        ReportedBy: macro@linux-mips.org
    Classification: Unclassified


We have two issues with dlopen [1] issued from static executables when
the global scope is accessed.

 First, an attempt to add a dynamic shared module to the global scope 
(i.e. with RTLD_GLOBAL requested) crashes like this:

Program received signal SIGSEGV, Segmentation fault.
add_to_global (new=0x49ef60) at dl-open.c:101
101           ns->_ns_global_scope_alloc

This is because at this point in static executables no global search list 
data structure has been initialised and as result the _ns_main_searchlist 
member of _dl_ns[LM_ID_BASE] (the initial namespace) is null.

 Second, an attempt to access the global scope itself (i.e. by using a 
null file name pointer) fails with an obscure error like:

/path/to/dir/: cannot read file data: Is a directory

(that can be retrieved with dlerror), where /path/to/dir/ is the first 
directory searched according to the dynamic load engine's shared module 
lookup policy.  This is because the null file name pointer is internally 
converted to an empty string, that is in turn looked for and then opened 
in the directories examined.  Of course that succeeds -- the directory 
itself is opened, but then the engine gets confused by the outcome and 
bails out.  The use of an empty string works in dynamic executables, 
because for them the dynamic loader has already prepared a link map 
referring to a file whose name is empty -- which, by means of how that 
code works, is the executable itself -- and that makes the loader abandon 
any file look-ups and use the link map already present.

 The two issues both boil down to the same bug -- no global scope present.

 Patch offered: http://sourceware.org/ml/libc-alpha/2013-01/msg00635.html

[1] http://pubs.opengroup.org/onlinepubs/7908799/xsh/dlopen.html

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