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

Message ID 20240307214032.2773074-1-josimmon@redhat.com
State Under Review
Delegated to: Carlos O'Donell
Headers
Series [v2] elf/rtld: Count skipped environment variables for enable_secure |

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Commit Message

Joe Simmons-Talbott March 7, 2024, 9:40 p.m. UTC
  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(-)
  

Comments

Joe Simmons-Talbott April 10, 2024, 7:58 p.m. UTC | #1
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
>
  
Andreas Schwab April 11, 2024, 1:45 p.m. UTC | #2
Can you please add a test?
  
Joe Simmons-Talbott April 11, 2024, 4:57 p.m. UTC | #3
Thanks for your review.  I added a testcase to the v3[1] patch that
triggers the assert without the patch and does not trigger the assert
with the patch.  I'm not certain it's a useful test though since it's
essentially testing that the assertion isn't triggered.

Thanks,
Joe

[1] https://sourceware.org/pipermail/libc-alpha/2024-April/156034.html

On Thu, Apr 11, 2024 at 9:46 AM Andreas Schwab <schwab@suse.de> wrote:
>
> Can you please add a test?
>
> --
> Andreas Schwab, SUSE Labs, schwab@suse.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."
>
  

Patch

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