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

[Carlos O'Donell]

On 3/7/24 09:44, Joe Simmons-Talbott 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);
> ---
>  elf/rtld.c | 26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/elf/rtld.c b/elf/rtld.c
> index ac4bb23652..089863a8fa 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 +2580,9 @@ process_envvars_secure (struct dl_main_state *state)
>    const char *nextp = UNSECURE_ENVVARS;
>    do
>      {
> +      if (getenv (nextp) != NULL)
> +        skip_env++;


Please add a detailed comment here about why the skip count is adjusted
based on the validity of the *next* pointer being non-NULL.

> +
>        unsetenv (nextp);
>        nextp = strchr (nextp, '\0') + 1;
>      }
> @@ -2590,6 +2595,8 @@ 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 +2750,16 @@ 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

-- 
Cheers,
Carlos.