[Bug dynamic-link/30601] New: ld.so should not use argv[0] as the dynamic linker name

["fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30601

            Bug ID: 30601
           Summary: ld.so should not use argv[0] as the dynamic linker
                    name
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
  Target Milestone: ---
             Flags: security-

Without an explicit loader invocation, the program name (in argv[0]) does not
matter for dynamic linking because it always set to "". But with an explicit
invocation, argv[0] ends up as an alias for the dynamic linker itself:

$ (exec -a libc.so.6 ld.so /usr/bin/cat)
/usr/bin/cat: libc.so.6: version `GLIBC_2.33' not found (required by
/usr/bin/cat)
/usr/bin/cat: libc.so.6: version `GLIBC_2.16' not found (required by
/usr/bin/cat)
/usr/bin/cat: libc.so.6: version `GLIBC_2.3.4' not found (required by
/usr/bin/cat)
/usr/bin/cat: libc.so.6: version `GLIBC_2.27' not found (required by
/usr/bin/cat)

This can be seen by attaching a debugger and inspecting l_name for the loader
map:

$ (exec -a foo ld.so /usr/bin/cat)

$ gdb -p  `pgrep ld.so`
(gdb) print _rtld_global._dl_rtld_map.l_name
$1 = 0x7ffe23a123b6 "foo"

(The pldd command does not work in this context, see bug 30600.)

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