elf: Ignore LD_PROFILE for setuid binaries

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

1 files changed, 3 insertions, 5 deletions

diff --git a/elf/rtld.c b/elf/rtld.c
index 51b6d9f..a09cf2a 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;