Re: [PATCH v2] elf/rtld: Count skipped environment variables for enable_secure

[Joe Simmons-Talbott <josimmon@redhat.com>]

Ping

On Thu, Mar 7, 2024 at 4:40 PM Joe Simmons-Talbott <josimmon@redhat.com> wrote:
>
> When using the glibc.rtld.enable_secure tunable we need to keep track of
> the count of environment variables we skip due to __libc_enable_secure
> being set and adjust the auxv section of the stack.  This fixes an
> assertion when running ld.so directly with glibc.rtld.enable_secure set.
>
> elf/rtld.c:1324   assert (auxv == sp + 1);
> ---
> Changes to v1:
> * Add comment explaining how and why skip_env is adjusted.
>
>  elf/rtld.c | 31 +++++++++++++++++++++++--------
>  1 file changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/elf/rtld.c b/elf/rtld.c
> index ac4bb23652..e9525ea987 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -155,7 +155,7 @@ static void dl_main_state_init (struct dl_main_state *state);
>     Since all of them start with `LD_' we are a bit smarter while finding
>     all the entries.  */
>  extern char **_environ attribute_hidden;
> -static void process_envvars (struct dl_main_state *state);
> +static int process_envvars (struct dl_main_state *state);
>
>  int _dl_argc attribute_relro attribute_hidden;
>  char **_dl_argv attribute_relro = NULL;
> @@ -1287,7 +1287,7 @@ rtld_setup_main_map (struct link_map *main_map)
>     _dl_argv and _dl_argc accordingly.  Those arguments are removed from
>     argv here.  */
>  static void
> -_dl_start_args_adjust (int skip_args)
> +_dl_start_args_adjust (int skip_args, int skip_env)
>  {
>    void **sp = (void **) (_dl_argv - skip_args - 1);
>    void **p = sp + skip_args;
> @@ -1319,7 +1319,7 @@ _dl_start_args_adjust (int skip_args)
>    while (*p != NULL);
>
>  #ifdef HAVE_AUX_VECTOR
> -  void **auxv = (void **) GLRO(dl_auxv) - skip_args;
> +  void **auxv = (void **) GLRO(dl_auxv) - skip_args - skip_env;
>    GLRO(dl_auxv) = (ElfW(auxv_t) *) auxv; /* Aliasing violation.  */
>    assert (auxv == sp + 1);
>
> @@ -1350,6 +1350,7 @@ dl_main (const ElfW(Phdr) *phdr,
>    unsigned int i;
>    bool rtld_is_main = false;
>    void *tcbp = NULL;
> +  int skip_env = 0;
>
>    struct dl_main_state state;
>    dl_main_state_init (&state);
> @@ -1363,7 +1364,7 @@ dl_main (const ElfW(Phdr) *phdr,
>  #endif
>
>    /* Process the environment variable which control the behaviour.  */
> -  process_envvars (&state);
> +  skip_env = process_envvars (&state);
>
>  #ifndef HAVE_INLINED_SYSCALLS
>    /* Set up a flag which tells we are just starting.  */
> @@ -1628,7 +1629,7 @@ dl_main (const ElfW(Phdr) *phdr,
>          _dl_argv[0] = argv0;
>
>        /* Adjust arguments for the application entry point.  */
> -      _dl_start_args_adjust (_dl_argv - orig_argv);
> +      _dl_start_args_adjust (_dl_argv - orig_argv, skip_env);
>      }
>    else
>      {
> @@ -2532,11 +2533,12 @@ a filename can be specified using the LD_DEBUG_OUTPUT environment variable.\n");
>      }
>  }
>
> -static void
> +static int
>  process_envvars_secure (struct dl_main_state *state)
>  {
>    char **runp = _environ;
>    char *envline;
> +  int skip_env = 0;
>
>    while ((envline = _dl_next_ld_env_entry (&runp)) != NULL)
>      {
> @@ -2578,6 +2580,14 @@ process_envvars_secure (struct dl_main_state *state)
>    const char *nextp = UNSECURE_ENVVARS;
>    do
>      {
> +      /* Keep track of the number of environment variables that were set in
> +         the environment and are unset below.  Use getenv() which returns
> +        non-NULL if the variable is set in the environment.  This count is
> +        needed if we need to adjust the location of the AUX vector on the
> +        stack when running ld.so directly. */
> +      if (getenv (nextp) != NULL)
> +        skip_env++;
> +
>        unsetenv (nextp);
>        nextp = strchr (nextp, '\0') + 1;
>      }
> @@ -2590,6 +2600,8 @@ process_envvars_secure (struct dl_main_state *state)
>        || state->mode != rtld_mode_normal
>        || state->version_info)
>      _exit (5);
> +
> +  return skip_env;
>  }
>
>  static void
> @@ -2743,13 +2755,16 @@ process_envvars_default (struct dl_main_state *state)
>      }
>  }
>
> -static void
> +static int
>  process_envvars (struct dl_main_state *state)
>  {
> +  int skip_env = 0;
>    if (__glibc_unlikely (__libc_enable_secure))
> -    process_envvars_secure (state);
> +    skip_env += process_envvars_secure (state);
>    else
>      process_envvars_default (state);
> +
> +  return skip_env;
>  }
>
>  #if HP_TIMING_INLINE
> --
> 2.43.2
>


-- 
Joe Simmons-Talbott