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#!/bin/sh
# Try to remove '/' recursively.
# Copyright (C) 2013-2019 Free Software Foundation, Inc.
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
print_ver_ rm
# POSIX mandates rm(1) to skip '/' arguments. This test verifies this mandated
# behavior as well as the --preserve-root and --no-preserve-root options.
# Especially the latter case is a live fire exercise as rm(1) is supposed to
# enter the unlinkat() system call. Therefore, limit the risk as much
# as possible -- if there's a bug this test would wipe the system out!
# Faint-hearted: skip this test for the 'root' user.
skip_if_root_
# Pull the teeth from rm(1) by intercepting the unlinkat() system call via the
# LD_PRELOAD environment variable. This requires shared libraries to work.
require_gcc_shared_
# Ensure this variable is unset as it's
# used later in the unlinkat() wrapper.
unset CU_TEST_SKIP_EXIT
# Set this to 0 if you don't have a working gdb but would
# still like to run the test
USE_GDB=1
if test $USE_GDB = 1; then
# Use gdb to provide further protection by limiting calls to unlinkat().
( timeout 10s gdb --version ) > gdb.out 2>&1
case $(cat gdb.out) in
*'GNU gdb'*) ;;
*) skip_ "can't run gdb";;
esac
fi
# Break on a line rather than a symbol, to cater for inline functions
break_src="$abs_top_srcdir/src/remove.c"
break_line=$(grep -n ^excise "$break_src") || framework_failure_
break_line=$(echo "$break_line" | cut -d: -f1) || framework_failure_
break_line="$break_src:$break_line"
cat > k.c <<'EOF' || framework_failure_
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int unlinkat (int dirfd, const char *pathname, int flags)
{
/* Prove that LD_PRELOAD works: create the evidence file "x". */
fclose (fopen ("x", "w"));
/* Immediately terminate, unless indicated otherwise. */
if (! getenv("CU_TEST_SKIP_EXIT"))
_exit (0);
/* Pretend success. */
return 0;
}
EOF
# Then compile/link it:
gcc_shared_ k.c k.so \
|| framework_failure_ 'failed to build shared library'
# Note breakpoint commands don't work in batch mode
# https://sourceware.org/bugzilla/show_bug.cgi?id=10079
# So we use python to script behavior upon hitting the breakpoint
cat > bp.py <<'EOF.py' || framework_failure_
def breakpoint_handler (event):
if not isinstance(event, gdb.BreakpointEvent):
return
hit_count = event.breakpoints[0].hit_count
if hit_count == 1:
gdb.execute('shell touch excise.break')
gdb.execute('continue')
elif hit_count > 2:
gdb.write('breakpoint hit twice already')
gdb.execute('quit 1')
else:
gdb.execute('continue')
gdb.events.stop.connect(breakpoint_handler)
EOF.py
# In order of the sed expressions below, this cleans:
#
# 1. gdb uses the full path when running rm, so remove the leading dirs.
# 2. For some of the "/" synonyms, the error diagnostic slightly differs from
# that of the basic "/" case (see gnulib's fts_open' and ROOT_DEV_INO_WARN):
# rm: it is dangerous to operate recursively on 'FILE' (same as '/')
# Strip that part off for the following comparison.
clean_rm_err_()
{
sed "s/.*rm: /rm: /; \
s/\(rm: it is dangerous to operate recursively on\).*$/\1 '\/'/"
}
#-------------------------------------------------------------------------------
# exercise_rm_r_root: shell function to test "rm -r '/'"
# The caller must provide the FILE to remove as well as any options
# which should be passed to 'rm'.
# Paranoia mode on:
# For the worst case where both rm(1) would fail to refuse to process the "/"
# argument (in the cases without the --no-preserve-root option), and
# intercepting the unlinkat(1) system call would fail (which actually already
# has been proven to work above), and the current non root user has
# write access to "/", limit the damage to the current file system via
# the --one-file-system option.
# Furthermore, run rm(1) via gdb that limits the number of unlinkat() calls.
exercise_rm_r_root ()
{
# Remove the evidence files; verify that.
rm -f x excise.break || framework_failure_
test -f x && framework_failure_
test -f excise.break && framework_failure_
local skip_exit=
if [ "$CU_TEST_SKIP_EXIT" = 1 ]; then
# Pass on this variable into 'rm's environment.
skip_exit='CU_TEST_SKIP_EXIT=1'
fi
if test $USE_GDB = 1; then
gdb -nx --batch-silent -return-child-result \
--eval-command="set exec-wrapper \
env 'LD_PRELOAD=$LD_PRELOAD:./k.so' $skip_exit" \
--eval-command="break '$break_line'" \
--eval-command='source bp.py' \
--eval-command="run -rv --one-file-system $*" \
--eval-command='quit' \
rm < /dev/null > out 2> err.t
else
touch excise.break
env LD_PRELOAD=$LD_PRELOAD:./k.so $skip_exit \
rm -rv --one-file-system $* < /dev/null > out 2> err.t
fi
ret=$?
clean_rm_err_ < err.t > err || ret=$?
return $ret
}
# Verify that "rm -r dir" basically works.
mkdir dir || framework_failure_
rm -r dir || framework_failure_
test -d dir && framework_failure_
# Now verify that intercepting unlinkat() works:
# rm(1) must succeed as before, but this time both the evidence file "x"
# and the test file / directory must still exist afterward.
mkdir dir || framework_failure_
> file || framework_failure_
skip=
for file in dir file ; do
exercise_rm_r_root "$file" || skip=1
test -e "$file" || skip=1
test -f x || skip=1
test -f excise.break || skip=1 # gdb works and breakpoint hit
compare /dev/null err || skip=1
test "$skip" = 1 \
&& { cat out; cat err; \
skip_ "internal test failure: maybe LD_PRELOAD or gdb doesn't work?"; }
done
# "rm -r /" without --no-preserve-root should output the following
# diagnostic error message.
cat <<EOD > exp || framework_failure_
rm: it is dangerous to operate recursively on '/'
rm: use --no-preserve-root to override this failsafe
EOD
#-------------------------------------------------------------------------------
# Exercise "rm -r /" without and with the --preserve-root option.
# Exercise various synonyms of "/" including symlinks to it.
# Expect a non-Zero exit status.
# Prepare a few symlinks to "/".
ln -s / rootlink || framework_failure_
ln -s rootlink rootlink2 || framework_failure_
ln -sr / rootlink3 || framework_failure_
for opts in \
'/' \
'--preserve-root /' \
'//' \
'///' \
'////' \
'rootlink/' \
'rootlink2/' \
'rootlink3/' ; do
returns_ 1 exercise_rm_r_root $opts || fail=1
# Expect nothing in 'out' and the above error diagnostic in 'err'.
# As rm(1) should have skipped the "/" argument, it does not call unlinkat().
# Therefore, the evidence file "x" should not exist.
compare /dev/null out || fail=1
compare exp err || fail=1
test -f x && fail=1
# Do nothing more if this test failed.
test $fail = 1 && { cat out; cat err; Exit $fail; }
done
#-------------------------------------------------------------------------------
# Exercise with --no-preserve to ensure shortened equivalent is not allowed.
cat <<EOD > exp_opt || framework_failure_
rm: you may not abbreviate the --no-preserve-root option
EOD
returns_ 1 exercise_rm_r_root --no-preserve / || fail=1
compare exp_opt err || fail=1
test -f x && fail=1
#-------------------------------------------------------------------------------
# Exercise "rm -r file1 / file2".
# Expect a non-Zero exit status representing failure to remove "/",
# yet 'file1' and 'file2' should be removed.
> file1 || framework_failure_
> file2 || framework_failure_
# Now that we know that 'rm' won't call the unlinkat() system function for "/",
# we could probably execute it without the LD_PRELOAD'ed safety net.
# Nevertheless, it's still better to use it for this test.
# Tell the unlinkat() replacement function to not _exit(0) immediately
# by setting the following variable.
CU_TEST_SKIP_EXIT=1
returns_ 1 exercise_rm_r_root --preserve-root file1 '/' file2 || fail=1
unset CU_TEST_SKIP_EXIT
cat <<EOD > out_removed
removed 'file1'
removed 'file2'
EOD
# The above error diagnostic should appear in 'err'.
# Both 'file1' and 'file2' should be removed. Simply verify that in the
# "out" file, as the replacement unlinkat() dummy did not remove them.
# Expect the evidence file "x" to exist.
compare out_removed out || fail=1
compare exp err || fail=1
test -f x || fail=1
# Do nothing more if this test failed.
test $fail = 1 && { cat out; cat err; Exit $fail; }
#-------------------------------------------------------------------------------
# Exercise various synonyms of "/" having a trailing "." or ".." in the name.
# This triggers another check in the code first and therefore leads to a
# different diagnostic. However, we want to test anyway to protect against
# future reordering of the checks in the code.
# Expect that other error diagnostic in 'err' and nothing in 'out'.
# Expect a non-Zero exit status. The evidence file "x" should not exist.
for file in \
'//.' \
'/./' \
'/.//' \
'/../' \
'/.././' \
'/etc/..' \
'rootlink/..' \
'rootlink2/.' \
'rootlink3/./' ; do
test -d "$file" || continue # if e.g. /etc does not exist.
returns_ 1 exercise_rm_r_root --preserve-root "$file" || fail=1
grep "rm: refusing to remove '\.' or '\.\.' directory: skipping" err \
|| fail=1
compare /dev/null out || fail=1
test -f x && fail=1
# Do nothing more if this test failed.
test $fail = 1 && { cat out; cat err; Exit $fail; }
done
#-------------------------------------------------------------------------------
# Until now, it was all just fun.
# Now exercise the --no-preserve-root option with which rm(1) should enter
# the intercepted unlinkat() system call.
# As the interception code terminates the process immediately via _exit(0),
# the exit status should be 0.
# Use the option --interactive=never to bypass the following prompt:
# "rm: descend into write-protected directory '/'?"
exercise_rm_r_root --interactive=never --no-preserve-root '/' \
|| fail=1
# The 'err' file should not contain the above error diagnostic.
grep "rm: it is dangerous to operate recursively on '/'" err && fail=1
# Instead, rm(1) should have called the intercepted unlinkat() function,
# i.e., the evidence file "x" should exist.
test -f x || fail=1
test $fail = 1 && { cat out; cat err; }
Exit $fail