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From: "ppluzhnikov at google dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/16046] New: dl_iterate_phdr should not expose internal stub
Date: Mon, 14 Oct 2013 20:34:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=16046

            Bug ID: 16046
           Summary: dl_iterate_phdr should not expose internal stub
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: ppluzhnikov at google dot com

Test case:

#define _GNU_SOURCE
#include <stdio.h>
#include <link.h>

int callback(struct dl_phdr_info *info, size_t size, void *data) {
  printf("addr=%p name=%s phdr=%p phnum=%d\n",
         (void*)info->dlpi_addr, info->dlpi_name, info->dlpi_phdr,
         info->dlpi_phnum);
  return 0;
}
int main() {
  int status;
  status = dl_iterate_phdr(callback, NULL);
  return 0;
}


Using current git trunk, dynamically linked binary shows:

addr=(nil) name= phdr=0x400040 phnum=9
addr=0x7fff2a613000 name=linux-vdso.so.1 phdr=0x7fff29d13040 phnum=4
addr=0x7f73a76d4000 name=./libc.so.6 phdr=0x7f73a76d4040 phnum=10
addr=0x7f73a7a87000 name=./elf/ld.so phdr=0x7f73a7a87040 phnum=7

Statically linked binary:

addr=(nil) name= phdr=0x400040 phnum=6
addr=(nil) name= phdr=(nil) phnum=0
addr=0x7ffffd5e1000 name=linux-vdso.so.1 phdr=0x7ffffcce1040 phnum=4

Same with glibc-2.15:
addr=(nil) name= phdr=0x400040 phnum=6


What is the second entry? People calling dl_iterate_phdr may legitimately
expect only real ELF images to appear.

At a minimum, this internal entry should be hidden from dl_iterate_phdr.

AFAICT, this was added in commit:

commit f91f1c0fb89056995f1c9c6a06c361efdf5139e7
Author: Maciej W. Rozycki <macro@codesourcery.com>
Date:   Fri Jun 28 16:20:26 2013 +0100

    [BZ #15022] Correct global-scope dlopen issues in static executables.

    This change creates a link map in static executables to serve as the
    global search list for dlopen.  It fixes a problem with the inability
    to access the global symbol object and a crash on an attempt to map a
    DSO into the global scope.  Some code that has become dead after the
    addition of this link map is removed too and test cases are provided.

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