Re: [PATCH v3 12/19] elf: Ignore LD_PROFILE for setuid binaries

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

On 2023-11-06 15:25, Adhemerval Zanella wrote:
> Loader does not ignore LD_PROFILE in secure-execution mode (different
> than man-page states [1]), rather it uses a different path
> (/var/profile) and ignore LD_PROFILE_OUTPUT.
> 
> Allowing secure-execution profiling is already a non good security
> boundary, since it enables different code paths and extra OS access by
> the process.  But by ignoring LD_PROFILE_OUTPUT, the resulting profile
> file might also be acceded in a racy manner since the file name does not
> use any process-specific information (such as pid, timing, etc.).
> 
> Another side-effect is it forces lazy binding even on libraries that
> might be with DF_BIND_NOW.
> 
> [1] https://man7.org/linux/man-pages/man8/ld.so.8.html
> ---

LGTM.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

>   elf/Makefile         |  3 +++
>   elf/rtld.c           |  8 +++-----
>   elf/tst-env-setuid.c | 12 +++++++++++-
>   3 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index 52981c19d0..08896bb895 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -2983,3 +2983,6 @@ $(objpfx)tst-dlclose-lazy.out: \
>     $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so
>   
>   tst-env-setuid-ARGS = -- $(host-test-program-cmd)
> +
> +# Reuse a module with a SONAME, to specific as the LD_PROFILE.
> +$(objpfx)tst-env-setuid: $(objpfx)tst-sonamemove-runmod2.so
> diff --git a/elf/rtld.c b/elf/rtld.c
> index 51b6d9f326..a09cf2a9df 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -361,6 +361,7 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
>       ._dl_fpu_control = _FPU_DEFAULT,
>       ._dl_pagesize = EXEC_PAGESIZE,
>       ._dl_inhibit_cache = 0,
> +    ._dl_profile_output = "/var/tmp",
>   
>       /* Function pointers.  */
>       ._dl_debug_printf = _dl_debug_printf,
> @@ -2534,10 +2535,6 @@ process_envvars (struct dl_main_state *state)
>     char *envline;
>     char *debug_output = NULL;
>   
> -  /* This is the default place for profiling data file.  */
> -  GLRO(dl_profile_output)
> -    = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
> -
>     while ((envline = _dl_next_ld_env_entry (&runp)) != NULL)
>       {
>         size_t len = 0;
> @@ -2586,7 +2583,8 @@ process_envvars (struct dl_main_state *state)
>   	    }
>   
>   	  /* Which shared object shall be profiled.  */
> -	  if (memcmp (envline, "PROFILE", 7) == 0 && envline[8] != '\0')
> +	  if (!__libc_enable_secure
> +	      && memcmp (envline, "PROFILE", 7) == 0 && envline[8] != '\0')
>   	    GLRO(dl_profile) = &envline[8];
>   	  break;
>   
> diff --git a/elf/tst-env-setuid.c b/elf/tst-env-setuid.c
> index ba295a6a14..76b8e1fb45 100644
> --- a/elf/tst-env-setuid.c
> +++ b/elf/tst-env-setuid.c
> @@ -34,6 +34,9 @@ static char SETGID_CHILD[] = "setgid-child";
>   
>   #define FILTERED_VALUE   "some-filtered-value"
>   #define UNFILTERED_VALUE "some-unfiltered-value"
> +/* It assumes no other programs is being profile with a library with same
> +   SONAME using the default folder.  */
> +#define PROFILE_LIB      "tst-sonamemove-runmod2.so"
>   
>   struct envvar_t
>   {
> @@ -50,7 +53,7 @@ static const struct envvar_t filtered_envvars[] =
>     { "LD_HWCAP_MASK",           FILTERED_VALUE },
>     { "LD_LIBRARY_PATH",         FILTERED_VALUE },
>     { "LD_PRELOAD",              FILTERED_VALUE },
> -  { "LD_PROFILE",              FILTERED_VALUE },
> +  { "LD_PROFILE",              "tst-sonamemove-runmod2.so" },
>     { "MALLOC_ARENA_MAX",        FILTERED_VALUE },
>     { "MALLOC_PERTURB_",         FILTERED_VALUE },
>     { "MALLOC_TRACE",            FILTERED_VALUE },
> @@ -87,6 +90,13 @@ test_child (void)
>         ret |= !(env != NULL && strcmp (env, e->value) == 0);
>       }
>   
> +  /* Also check if no profile file was created.  */
> +  {
> +    char *profilepath = xasprintf ("/var/tmp/%s.profile", PROFILE_LIB);
> +    ret |= !access (profilepath, R_OK);
> +    free (profilepath);
> +  }
> +
>     return ret;
>   }
>