selftests/exec: Add binfmt_script regression test

CFLAGS += -Wno-nonnull

CFLAGS += -D_GNU_SOURCE

TEST_PROGS := binfmt_script

TEST_GEN_PROGS := execveat

TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir

# Makefile is a run-time dependency, since it's accessed by the execveat test

#!/usr/bin/env python3

# SPDX-License-Identifier: GPL-2.0

#

# Test that truncation of bprm->buf doesn't cause unexpected execs paths, along

# with various other pathological cases.

import os, subprocess

# Relevant commits

#

# b5372fe5dc84 ("exec: load_script: Do not exec truncated interpreter path")

# 6eb3c3d0a52d ("exec: increase BINPRM_BUF_SIZE to 256")

# BINPRM_BUF_SIZE

SIZE=256

NAME_MAX=int(subprocess.check_output(["getconf", "NAME_MAX", "."]))

test_num=0

code='''#!/usr/bin/perl

print "Executed interpreter! Args:\n";

print "0 : '$0'\n";

$counter = 1;

foreach my $a (@ARGV) {

    print "$counter : '$a'\n";

    $counter++;

}

'''

##

# test - produce a binfmt_script hashbang line for testing

#

# @size:     bytes for bprm->buf line, including hashbang but not newline

# @good:     whether this script is expected to execute correctly

# @hashbang: the special 2 bytes for running binfmt_script

# @leading:  any leading whitespace before the executable path

# @root:     start of executable pathname

# @target:   end of executable pathname

# @arg:      bytes following the executable pathname

# @fill:     character to fill between @root and @target to reach @size bytes

# @newline:  character to use as newline, not counted towards @size

# ...

def test(name, size, good=True, leading="", root="./", target="/perl",

                     fill="A", arg="", newline="\n", hashbang="#!"):

    global test_num, tests, NAME_MAX

    test_num += 1

    if test_num > tests:

        raise ValueError("more binfmt_script tests than expected! (want %d, expected %d)"

                         % (test_num, tests))

    middle = ""

    remaining = size - len(hashbang) - len(leading) - len(root) - len(target) - len(arg)

    # The middle of the pathname must not exceed NAME_MAX

    while remaining >= NAME_MAX:

        middle += fill * (NAME_MAX - 1)

        middle += '/'

        remaining -= NAME_MAX

    middle += fill * remaining

    dirpath = root + middle

    binary = dirpath + target

    if len(target):

        os.makedirs(dirpath, mode=0o755, exist_ok=True)

        open(binary, "w").write(code)

        os.chmod(binary, 0o755)

    buf=hashbang + leading + root + middle + target + arg + newline

    if len(newline) > 0:

        buf += 'echo this is not really perl\n'

    script = "binfmt_script-%s" % (name)

    open(script, "w").write(buf)

    os.chmod(script, 0o755)

    proc = subprocess.Popen(["./%s" % (script)], shell=True,

                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT)

    stdout = proc.communicate()[0]

    if proc.returncode == 0 and b'Executed interpreter' in stdout:

        if good:

            print("ok %d - binfmt_script %s (successful good exec)"

                  % (test_num, name))

        else:

            print("not ok %d - binfmt_script %s succeeded when it should have failed"

                  % (test_num, name))

    else:

        if good:

            print("not ok %d - binfmt_script %s failed when it should have succeeded (rc:%d)"

                  % (test_num, name, proc.returncode))

        else:

            print("ok %d - binfmt_script %s (correctly failed bad exec)"

                  % (test_num, name))

    # Clean up crazy binaries

    os.unlink(script)

    if len(target):

        elements = binary.split('/')

        os.unlink(binary)

        elements.pop()

        while len(elements) > 1:

            os.rmdir("/".join(elements))

            elements.pop()

tests=27

print("TAP version 1.3")

print("1..%d" % (tests))

### FAIL (8 tests)

# Entire path is well past the BINFMT_BUF_SIZE.

test(name="too-big",        size=SIZE+80, good=False)

# Path is right at max size, making it impossible to tell if it was truncated.

test(name="exact",          size=SIZE,    good=False)

# Same as above, but with leading whitespace.

test(name="exact-space",    size=SIZE,    good=False, leading=" ")

# Huge buffer of only whitespace.

test(name="whitespace-too-big", size=SIZE+71, good=False, root="",

                                              fill=" ", target="")

# A good path, but it gets truncated due to leading whitespace.

test(name="truncated",      size=SIZE+17, good=False, leading=" " * 19)

# Entirely empty except for #!

test(name="empty",          size=2,       good=False, root="",

                                          fill="", target="", newline="")

# Within size, but entirely spaces

test(name="spaces",         size=SIZE-1,  good=False, root="", fill=" ",

                                          target="", newline="")

# Newline before binary.

test(name="newline-prefix", size=SIZE-1,  good=False, leading="\n",

                                          root="", fill=" ", target="")

### ok (19 tests)

# The original test case that was broken by commit:

# 8099b047ecc4 ("exec: load_script: don't blindly truncate shebang string")

test(name="test.pl",        size=439, leading=" ",

     root="./nix/store/bwav8kz8b3y471wjsybgzw84mrh4js9-perl-5.28.1/bin",

     arg=" -I/nix/store/x6yyav38jgr924nkna62q3pkp0dgmzlx-perl5.28.1-File-Slurp-9999.25/lib/perl5/site_perl -I/nix/store/ha8v67sl8dac92r9z07vzr4gv1y9nwqz-perl5.28.1-Net-DBus-1.1.0/lib/perl5/site_perl -I/nix/store/dcrkvnjmwh69ljsvpbdjjdnqgwx90a9d-perl5.28.1-XML-Parser-2.44/lib/perl5/site_perl -I/nix/store/rmji88k2zz7h4zg97385bygcydrf2q8h-perl5.28.1-XML-Twig-3.52/lib/perl5/site_perl")

# One byte under size, leaving newline visible.

test(name="one-under",           size=SIZE-1)

# Two bytes under size, leaving newline visible.

test(name="two-under",           size=SIZE-2)

# Exact size, but trailing whitespace visible instead of newline

test(name="exact-trunc-whitespace", size=SIZE, arg=" ")

# Exact size, but trailing space and first arg char visible instead of newline.

test(name="exact-trunc-arg",     size=SIZE, arg=" f")

# One bute under, with confirmed non-truncated arg since newline now visible.

test(name="one-under-full-arg",  size=SIZE-1, arg=" f")

# Short read buffer by one byte.

test(name="one-under-no-nl",     size=SIZE-1, newline="")

# Short read buffer by half buffer size.

test(name="half-under-no-nl",    size=int(SIZE/2), newline="")

# One byte under with whitespace arg. leaving wenline visible.

test(name="one-under-trunc-arg", size=SIZE-1, arg=" ")

# One byte under with whitespace leading. leaving wenline visible.

test(name="one-under-leading",   size=SIZE-1, leading=" ")

# One byte under with whitespace leading and as arg. leaving newline visible.

test(name="one-under-leading-trunc-arg",  size=SIZE-1, leading=" ", arg=" ")

# Same as above, but with 2 bytes under

test(name="two-under-no-nl",     size=SIZE-2, newline="")

test(name="two-under-trunc-arg", size=SIZE-2, arg=" ")

test(name="two-under-leading",   size=SIZE-2, leading=" ")

test(name="two-under-leading-trunc-arg",   size=SIZE-2, leading=" ", arg=" ")

# Same as above, but with buffer half filled

test(name="two-under-no-nl",     size=int(SIZE/2), newline="")

test(name="two-under-trunc-arg", size=int(SIZE/2), arg=" ")

test(name="two-under-leading",   size=int(SIZE/2), leading=" ")

test(name="two-under-lead-trunc-arg", size=int(SIZE/2), leading=" ", arg=" ")

if test_num != tests:

    raise ValueError("fewer binfmt_script tests than expected! (ran %d, expected %d"

                     % (test_num, tests))