diff mbox series

[v4,1/2] rtld: Add --no-default-paths option

Message ID 20210706102132.2170854-2-sidereal@google.com
State New
Headers show
Series [v4,1/2] rtld: Add --no-default-paths option | expand

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Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Fergus Dall July 6, 2021, 10:21 a.m. UTC
This option causes the default library search path to be skipped,
using only the paths in DT_RPATH, LD_LIBRARY_PATH, and
DT_RUNPATH. This option implies --inhibit-cache, as there is no point
in searching a cache of system libraries when we are not using the
system libraries at all.

This is necessary to preserve negative search results when isolating
applications from the system libraries. This can be important when an
application uses dlopen at run time to load optional libraries.

When a shared library is required by the application, it can be
isolated by putting appropriate versions of the libraries in
directories specified in LD_LIBRARY_PATH, because the library search
will always terminate before potentially loading any system libraries.

On the other hand, if the application should be run without an
optional library, the search will proceed past the LD_LIBRARY_PATH
directories into the default system libraries, potentially causing an
incorrect library to be linked.
---
 NEWS                       |  4 ++++
 elf/dl-load.c              |  6 ++++--
 elf/dl-support.c           |  2 ++
 elf/dl-usage.c             |  2 ++
 elf/rtld.c                 | 10 ++++++++++
 sysdeps/generic/ldsodefs.h |  3 +++
 6 files changed, 25 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/NEWS b/NEWS
index 8e72946c3f..790034d837 100644
--- a/NEWS
+++ b/NEWS
@@ -60,6 +60,10 @@  Major new features:
   to call async-signal-safe functions (such as raise or execve).  This function
   is currently a GNU extension.
 
+* The dynamic linker has gained the --no-default-paths option, which
+  causes it to ignore libraries in the default (compiled in) system
+  paths even if all higher precedence locations have been searched.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * The function pthread_mutex_consistent_np has been deprecated; programs
diff --git a/elf/dl-load.c b/elf/dl-load.c
index a08df001af..0a14cbb87c 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -2258,7 +2258,8 @@  _dl_map_object (struct link_map *loader, const char *name,
       if (fd == -1
 	  && ((l = loader ?: GL(dl_ns)[nsid]._ns_loaded) == NULL
 	      || __glibc_likely (!(l->l_flags_1 & DF_1_NODEFLIB)))
-	  && __rtld_search_dirs.dirs != (void *) -1)
+	  && __rtld_search_dirs.dirs != (void *) -1
+	  && __glibc_likely (GLRO(dl_search_default_paths)))
 	fd = open_path (name, namelen, mode, &__rtld_search_dirs,
 			&realname, &fb, l, LA_SER_DEFAULT, &found_other_class);
 
@@ -2438,7 +2439,8 @@  _dl_rtld_di_serinfo (struct link_map *loader, Dl_serinfo *si, bool counting)
      a way to indicate that in the results for Dl_serinfo.  */
 
   /* Finally, try the default path.  */
-  if (!(loader->l_flags_1 & DF_1_NODEFLIB))
+  if (!(loader->l_flags_1 & DF_1_NODEFLIB)
+      && __glibc_likely (GLRO(dl_search_default_paths)))
     add_path (&p, &__rtld_search_dirs, XXX_default);
 
   if (counting)
diff --git a/elf/dl-support.c b/elf/dl-support.c
index dfc9ab760e..def75550aa 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -144,6 +144,8 @@  size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
 
 int _dl_inhibit_cache;
 
+int _dl_search_default_paths;
+
 unsigned int _dl_osversion;
 
 /* All known directories in sorted order.  */
diff --git a/elf/dl-usage.c b/elf/dl-usage.c
index 5ad3a72559..b5ae44932a 100644
--- a/elf/dl-usage.c
+++ b/elf/dl-usage.c
@@ -247,6 +247,8 @@  setting environment variables (which would be inherited by subprocesses).\n\
   --inhibit-cache       Do not use " LD_SO_CACHE "\n\
   --library-path PATH   use given PATH instead of content of the environment\n\
                         variable LD_LIBRARY_PATH\n\
+  --no-default-paths    do not use the default library search path\n\
+                        (this option implies --inhibit-cache)\n\
   --glibc-hwcaps-prepend LIST\n\
                         search glibc-hwcaps subdirectories in LIST\n\
   --glibc-hwcaps-mask LIST\n\
diff --git a/elf/rtld.c b/elf/rtld.c
index fbbd60b446..8eb76b8998 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -360,6 +360,7 @@  struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_fpu_control = _FPU_DEFAULT,
     ._dl_pagesize = EXEC_PAGESIZE,
     ._dl_inhibit_cache = 0,
+    ._dl_search_default_paths = 1,
 
     /* Function pointers.  */
     ._dl_debug_printf = _dl_debug_printf,
@@ -1204,6 +1205,15 @@  dl_main (const ElfW(Phdr) *phdr,
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
+	else if (! strcmp (_dl_argv[1], "--no-default-paths"))
+	  {
+	    GLRO(dl_search_default_paths) = 0;
+	    GLRO(dl_inhibit_cache) = 1;
+
+	    ++_dl_skip_args;
+	    --_dl_argc;
+	    ++_dl_argv;
+	  }
 	else if (! strcmp (_dl_argv[1], "--inhibit-rpath")
 		 && _dl_argc > 2)
 	  {
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 176394de4d..d7c9b9e477 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -551,6 +551,9 @@  struct rtld_global_ro
   /* Do we read from ld.so.cache?  */
   EXTERN int _dl_inhibit_cache;
 
+  /* Do we search the default system paths?  */
+  EXTERN int _dl_search_default_paths;
+
   /* Copy of the content of `_dl_main_searchlist' at startup time.  */
   EXTERN struct r_scope_elem _dl_initial_searchlist;