[Bug 5168] New: LD_PRELOAD does not work as documented for SUID binaries

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=5168

           Summary: LD_PRELOAD does not work as documented for SUID
                    binaries
           Product: uClibc
           Version: 0.9.32
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: minor
          Priority: P5
         Component: Shared Library Support
        AssignedTo: unassigned at uclibc.org
        ReportedBy: erik at ejohansson.se
                CC: uclibc-cvs at uclibc.org
   Estimated Hours: 0.0


According to the help for LDSO_PRELOAD_ENV_SUPPORT: "For
set-user-ID/set-group-ID ELF binaries, only libraries in the standard search
directories that are also set-user-ID will be loaded."

However, this does not work. 

Looking at _dl_get_ready_to_run() in ldso/ldso/ldso.c it seems that LD_PRELOAD
and _dl_preload is unset when _dl_secure is 1. This looks incorrect as
_dl_load_elf_shared_library() in ldso/ldso/dl-elf.c seems to only allow loading
of SUID libraries when _dl_secure is 1.

Without having tested it, perhaps it would be enough to replace:
_dl_preload = NULL;

in ldso.c with:
_dl_preload = _dl_getenv("LD_PRELOAD", envp);

and moving the statement before the while that unsets unsecure envvars?

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