Re: [PATCH v4] elf/rtld: Count skipped environment variables for enable_secure

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 12/04/24 12:21, 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.
> Add a testcase that ensures the assert is not hit.
> 
> elf/rtld.c:1324   assert (auxv == sp + 1);

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
> Changes to v3:
> * Run the testcase with ld.so explicitly.
> 
> Changes to v2:
> * Add testcase that triggers the assertion before this patch and does
>   not after the patch.
> 
> Changes to v1:
> * Add comment explaining how and why skip_env is adjusted.
> 
>  elf/Makefile                         | 10 +++++++++
>  elf/rtld.c                           | 31 +++++++++++++++++++-------
>  elf/tst-tunables-enable_secure-env.c | 33 ++++++++++++++++++++++++++++
>  3 files changed, 66 insertions(+), 8 deletions(-)
>  create mode 100644 elf/tst-tunables-enable_secure-env.c
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index 6dad11bcfb..ea8a078f3e 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -315,6 +315,7 @@ tests := \
>    tst-leaks1 \
>    tst-stringtable \
>    tst-tls9 \
> +  tst-tunables-enable_secure-env \
>    # tests
>  
>  tests-internal := \
> @@ -1189,6 +1190,7 @@ tests-special += \
>    $(objpfx)tst-trace3.out \
>    $(objpfx)tst-trace4.out \
>    $(objpfx)tst-trace5.out \
> +  $(objpfx)tst-tunables-enable_secure-env.out \
>    $(objpfx)tst-unused-dep-cmp.out \
>    $(objpfx)tst-unused-dep.out \
>    # tests-special
> @@ -2216,6 +2218,14 @@ $(objpfx)tst-unused-dep-cmp.out: $(objpfx)tst-unused-dep.out
>  	cmp $< /dev/null > $@; \
>  	$(evaluate-test)
>  
> +$(objpfx)tst-tunables-enable_secure-env.out: $(objpfx)tst-tunables-enable_secure-env
> +	$(test-wrapper-env) \
> +	GLIBC_TUNABLES=glibc.rtld.enable_secure=1 \
> +	$(rtld-prefix) \
> +	  $< > $@; \
> +	$(evaluate-test)
> +
> +
>  $(objpfx)tst-audit11.out: $(objpfx)tst-auditmod11.so $(objpfx)tst-audit11mod1.so
>  tst-audit11-ENV = LD_AUDIT=$(objpfx)tst-auditmod11.so
>  $(objpfx)tst-audit11mod1.so: $(objpfx)tst-audit11mod2.so
> diff --git a/elf/rtld.c b/elf/rtld.c
> index 18d73f19c6..d116a436f5 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;
> @@ -1289,7 +1289,7 @@ 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;
> @@ -1321,7 +1321,7 @@ _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);
>  
> @@ -1352,6 +1352,7 @@ 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);
> @@ -1365,7 +1366,7 @@ 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.  */
> @@ -1630,7 +1631,7 @@ 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
>      {
> @@ -2534,11 +2535,12 @@ a filename can be specified using the LD_DEBUG_OUTPUT environment variable.\n");
>      }
>  }
>  \f
> -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)
>      {
> @@ -2580,6 +2582,14 @@ 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;
>      }
> @@ -2592,6 +2602,8 @@ process_envvars_secure (struct dl_main_state *state)
>        || state->mode != rtld_mode_normal
>        || state->version_info)
>      _exit (5);
> +
> +  return skip_env;
>  }
>  
>  static void
> @@ -2745,13 +2757,16 @@ 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
> diff --git a/elf/tst-tunables-enable_secure-env.c b/elf/tst-tunables-enable_secure-env.c
> new file mode 100644
> index 0000000000..24e846f299
> --- /dev/null
> +++ b/elf/tst-tunables-enable_secure-env.c
> @@ -0,0 +1,33 @@
> +/* Check enable_secure tunable handles removed ENV variables without
> +   assertions.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <support/capture_subprocess.h>
> +#include <support/check.h>
> +
> +static int
> +do_test (int argc, char *argv[])
> +{
> +  /* Ensure that no assertions are hit when a dynamically linked application
> +     runs.  This test requires that GLIBC_TUNABLES=glibc.rtld.enable_secure=1
> +     is set. */
> +  return 0;
> +}
> +
> +#define TEST_FUNCTION_ARGV do_test
> +#include <support/test-driver.c>