libstdc++: Avoid symlink race in filesystem::remove_all [PR104161]

This adds a new internal flag to the filesystem::directory_iterator
constructor that makes it fail if the path is a symlink that resolves to
a directory. This prevents filesystem::remove_all from following a
symlink to a directory, rather than deleting the symlink itself.

We can also use that new flag in recursive_directory_iterator to ensure
that we don't follow symlinks if the follow_directory_symlink option is
not set.

This also moves an error check in filesystem::remove_all after the while
loop, so that errors from the directory_iterator constructor are
reproted, instead of continuing to the filesystem::remove call below.

libstdc++-v3/ChangeLog:

	PR libstdc++/104161
	* acinclude.m4 (GLIBCXX_CHECK_FILESYSTEM_DEPS): Check for
	fdopendir.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* src/c++17/fs_dir.cc (_Dir): Add nofollow flag to constructor
	and pass it to base class constructor.
	(directory_iterator): Pass nofollow flag to _Dir constructor.
	(fs::recursive_directory_iterator::increment): Likewise.
	* src/c++17/fs_ops.cc (do_remove_all): Use nofollow option for
	directory_iterator constructor. Move error check outside loop.
	* src/filesystem/dir-common.h (_Dir_base): Add nofollow flag to
	constructor and when it's set use ::open with O_NOFOLLOW and
	O_DIRECTORY.
	* src/filesystem/dir.cc (_Dir): Add nofollow flag to constructor
	and pass it to base class constructor.
	(directory_iterator): Pass nofollow flag to _Dir constructor.
	(fs::recursive_directory_iterator::increment): Likewise.
	* src/filesystem/ops.cc (remove_all): Use nofollow option for
	directory_iterator constructor. Move error check outside loop.

1 files changed, 55 insertions, 0 deletions

diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 4c20c669144..5c6e51f5c11 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -77030,6 +77030,61 @@ $as_echo "$glibcxx_cv_truncate" >&6; }
 $as_echo "#define HAVE_TRUNCATE 1" >>confdefs.h
 
   fi
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for fdopendir" >&5
+$as_echo_n "checking for fdopendir... " >&6; }
+if ${glibcxx_cv_fdopendir+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+      if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <dirent.h>
+int
+main ()
+{
+::fdopendir(1);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_fdopendir=yes
+else
+  glibcxx_cv_fdopendir=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+  if test x$gcc_no_link = xyes; then
+  as_fn_error $? "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
+fi
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <dirent.h>
+int
+main ()
+{
+::fdopendir(1);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_fdopendir=yes
+else
+  glibcxx_cv_fdopendir=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_fdopendir" >&5
+$as_echo "$glibcxx_cv_fdopendir" >&6; }
+  if test $glibcxx_cv_truncate = yes; then
+
+$as_echo "#define HAVE_FDOPENDIR 1" >>confdefs.h
+
+  fi
   CXXFLAGS="$ac_save_CXXFLAGS"
   ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'