linux-yocto/tools/testing/selftests/exec/binfmt_script

#!/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

b5372fe5dc ("exec: load_script: Do not exec truncated interpreter path")

6eb3c3d0a5 ("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:

8099b047ec ("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))