chroot: call chroot() unconditionally to handle bind mounted "/"

* src/chroot.c (is_root): Adjust to compare canonicalized paths
rather than inodes, to handle (return false in) the case where
we have a tree that is constructed by first bind mounting "/"
(thus having the same inode).
(main): Unconditionally call chroot() because it's safer
and of minimal performance benefit to avoid in this case.
This will cause inconsistency with some platforms
not allowing `chroot / true` for non root users.
* tests/misc/chroot-fail.sh: Adjust appropriately.
* NEWS: Mention the bug fixes.
Fixes http://bugs.gnu.org/18736

1 files changed, 26 insertions, 20 deletions

diff --git a/tests/misc/chroot-fail.sh b/tests/misc/chroot-fail.sh
index 82ae23cdb..75f724a87 100755
--- a/tests/misc/chroot-fail.sh
+++ b/tests/misc/chroot-fail.sh
@@ -29,14 +29,18 @@ test $? = 125 || fail=1
 chroot --- / true # unknown option
 test $? = 125 || fail=1
 
-# Note chroot("/") succeeds for non-root users on some systems, but not all,
-# however we avoid the chroot() with "/" to have common behavior.
-chroot / sh -c 'exit 2' # exit status propagation
-test $? = 2 || fail=1
-chroot / . # invalid command
-test $? = 126 || fail=1
-chroot / no_such # no such command
-test $? = 127 || fail=1
+# chroot("/") succeeds for non-root users on some systems, but not all.
+if chroot / true ; then
+  can_chroot_root=1
+  chroot / sh -c 'exit 2' # exit status propagation
+  test $? = 2 || fail=1
+  chroot / . # invalid command
+  test $? = 126 || fail=1
+  chroot / no_such # no such command
+  test $? = 127 || fail=1
+else
+  test $? = 125 || fail=1
+fi
 
 # Ensure that --skip-chdir fails with a non-"/" argument.
 cat <<\EOF > exp || framework_failure_
@@ -47,17 +51,19 @@ chroot --skip-chdir . env pwd >out 2>err && fail=1
 compare /dev/null out || fail=1
 compare exp err || fail=1
 
-# Ensure we don't chroot("/") when NEWROOT is old "/".
-ln -s / isroot || framework_failure_
-for dir in '/' '/.' '/../' isroot; do
-  # Verify that chroot(1) succeeds and performs chdir("/")
-  # (chroot(1) of coreutils-8.23 failed to run the latter).
-  curdir=$(chroot "$dir" env pwd) || fail=1
-  test "$curdir" = '/' || fail=1
-
-  # Test the "--skip-chdir" option.
-  curdir=$(chroot --skip-chdir "$dir" env pwd) || fail=1
-  test "$curdir" = '/' && fail=1
-done
+# Ensure we chdir("/") appropriately when NEWROOT is old "/".
+if test "$can_chroot_root"; then
+  ln -s / isroot || framework_failure_
+  for dir in '/' '/.' '/../' isroot; do
+    # Verify that chroot(1) succeeds and performs chdir("/")
+    # (chroot(1) of coreutils-8.23 failed to run the latter).
+    curdir=$(chroot "$dir" env pwd) || fail=1
+    test "$curdir" = '/' || fail=1
+
+    # Test the "--skip-chdir" option.
+    curdir=$(chroot --skip-chdir "$dir" env pwd) || fail=1
+    test "$curdir" = '/' && fail=1
+  done
+fi
 
 Exit $fail