xref: /linux/tools/testing/selftests/exec/binfmt_script.py (revision 2a2dfc869d3345ccdd91322b023f4b0da84acbe7) 
1#!/usr/bin/env python3
2# SPDX-License-Identifier: GPL-2.0
3#
4# Test that truncation of bprm->buf doesn't cause unexpected execs paths, along
5# with various other pathological cases.
6import os, subprocess
7
8# Relevant commits
9#
10# b5372fe5dc84 ("exec: load_script: Do not exec truncated interpreter path")
11# 6eb3c3d0a52d ("exec: increase BINPRM_BUF_SIZE to 256")
12
13# BINPRM_BUF_SIZE
14SIZE=256
15
16NAME_MAX=int(subprocess.check_output(["getconf", "NAME_MAX", "."]))
17
18test_num=0
19
20code='''#!/usr/bin/perl
21print "Executed interpreter! Args:\n";
22print "0 : '$0'\n";
23$counter = 1;
24foreach my $a (@ARGV) {
25    print "$counter : '$a'\n";
26    $counter++;
27}
28'''
29
30##
31# test - produce a binfmt_script hashbang line for testing
32#
33# @size:     bytes for bprm->buf line, including hashbang but not newline
34# @good:     whether this script is expected to execute correctly
35# @hashbang: the special 2 bytes for running binfmt_script
36# @leading:  any leading whitespace before the executable path
37# @root:     start of executable pathname
38# @target:   end of executable pathname
39# @arg:      bytes following the executable pathname
40# @fill:     character to fill between @root and @target to reach @size bytes
41# @newline:  character to use as newline, not counted towards @size
42# ...
43def test(name, size, good=True, leading="", root="./", target="/perl",
44                     fill="A", arg="", newline="\n", hashbang="#!"):
45    global test_num, tests, NAME_MAX
46    test_num += 1
47    if test_num > tests:
48        raise ValueError("more binfmt_script tests than expected! (want %d, expected %d)"
49                         % (test_num, tests))
50
51    middle = ""
52    remaining = size - len(hashbang) - len(leading) - len(root) - len(target) - len(arg)
53    # The middle of the pathname must not exceed NAME_MAX
54    while remaining >= NAME_MAX:
55        middle += fill * (NAME_MAX - 1)
56        middle += '/'
57        remaining -= NAME_MAX
58    middle += fill * remaining
59
60    dirpath = root + middle
61    binary = dirpath + target
62    if len(target):
63        os.makedirs(dirpath, mode=0o755, exist_ok=True)
64        open(binary, "w").write(code)
65        os.chmod(binary, 0o755)
66
67    buf=hashbang + leading + root + middle + target + arg + newline
68    if len(newline) > 0:
69        buf += 'echo this is not really perl\n'
70
71    script = "binfmt_script-%s" % (name)
72    open(script, "w").write(buf)
73    os.chmod(script, 0o755)
74
75    proc = subprocess.Popen(["./%s" % (script)], shell=True,
76                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
77    stdout = proc.communicate()[0]
78
79    if proc.returncode == 0 and b'Executed interpreter' in stdout:
80        if good:
81            print("ok %d - binfmt_script %s (successful good exec)"
82                  % (test_num, name))
83        else:
84            print("not ok %d - binfmt_script %s succeeded when it should have failed"
85                  % (test_num, name))
86    else:
87        if good:
88            print("not ok %d - binfmt_script %s failed when it should have succeeded (rc:%d)"
89                  % (test_num, name, proc.returncode))
90        else:
91            print("ok %d - binfmt_script %s (correctly failed bad exec)"
92                  % (test_num, name))
93
94    # Clean up crazy binaries
95    os.unlink(script)
96    if len(target):
97        elements = binary.split('/')
98        os.unlink(binary)
99        elements.pop()
100        while len(elements) > 1:
101            os.rmdir("/".join(elements))
102            elements.pop()
103
104tests=27
105print("TAP version 1.3")
106print("1..%d" % (tests))
107
108### FAIL (8 tests)
109
110# Entire path is well past the BINFMT_BUF_SIZE.
111test(name="too-big",        size=SIZE+80, good=False)
112# Path is right at max size, making it impossible to tell if it was truncated.
113test(name="exact",          size=SIZE,    good=False)
114# Same as above, but with leading whitespace.
115test(name="exact-space",    size=SIZE,    good=False, leading=" ")
116# Huge buffer of only whitespace.
117test(name="whitespace-too-big", size=SIZE+71, good=False, root="",
118                                              fill=" ", target="")
119# A good path, but it gets truncated due to leading whitespace.
120test(name="truncated",      size=SIZE+17, good=False, leading=" " * 19)
121# Entirely empty except for #!
122test(name="empty",          size=2,       good=False, root="",
123                                          fill="", target="", newline="")
124# Within size, but entirely spaces
125test(name="spaces",         size=SIZE-1,  good=False, root="", fill=" ",
126                                          target="", newline="")
127# Newline before binary.
128test(name="newline-prefix", size=SIZE-1,  good=False, leading="\n",
129                                          root="", fill=" ", target="")
130
131### ok (19 tests)
132
133# The original test case that was broken by commit:
134# 8099b047ecc4 ("exec: load_script: don't blindly truncate shebang string")
135test(name="test.pl",        size=439, leading=" ",
136     root="./nix/store/bwav8kz8b3y471wjsybgzw84mrh4js9-perl-5.28.1/bin",
137     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")
138# One byte under size, leaving newline visible.
139test(name="one-under",           size=SIZE-1)
140# Two bytes under size, leaving newline visible.
141test(name="two-under",           size=SIZE-2)
142# Exact size, but trailing whitespace visible instead of newline
143test(name="exact-trunc-whitespace", size=SIZE, arg=" ")
144# Exact size, but trailing space and first arg char visible instead of newline.
145test(name="exact-trunc-arg",     size=SIZE, arg=" f")
146# One bute under, with confirmed non-truncated arg since newline now visible.
147test(name="one-under-full-arg",  size=SIZE-1, arg=" f")
148# Short read buffer by one byte.
149test(name="one-under-no-nl",     size=SIZE-1, newline="")
150# Short read buffer by half buffer size.
151test(name="half-under-no-nl",    size=int(SIZE/2), newline="")
152# One byte under with whitespace arg. leaving wenline visible.
153test(name="one-under-trunc-arg", size=SIZE-1, arg=" ")
154# One byte under with whitespace leading. leaving wenline visible.
155test(name="one-under-leading",   size=SIZE-1, leading=" ")
156# One byte under with whitespace leading and as arg. leaving newline visible.
157test(name="one-under-leading-trunc-arg",  size=SIZE-1, leading=" ", arg=" ")
158# Same as above, but with 2 bytes under
159test(name="two-under-no-nl",     size=SIZE-2, newline="")
160test(name="two-under-trunc-arg", size=SIZE-2, arg=" ")
161test(name="two-under-leading",   size=SIZE-2, leading=" ")
162test(name="two-under-leading-trunc-arg",   size=SIZE-2, leading=" ", arg=" ")
163# Same as above, but with buffer half filled
164test(name="two-under-no-nl",     size=int(SIZE/2), newline="")
165test(name="two-under-trunc-arg", size=int(SIZE/2), arg=" ")
166test(name="two-under-leading",   size=int(SIZE/2), leading=" ")
167test(name="two-under-lead-trunc-arg", size=int(SIZE/2), leading=" ", arg=" ")
168
169if test_num != tests:
170    raise ValueError("fewer binfmt_script tests than expected! (ran %d, expected %d"
171                     % (test_num, tests))
172