While working on commit b5372fe5dc84 ("exec: load_script: Do not exec truncated interpreter path"), I wrote a series of test scripts to verify corner cases. However, soon after, commit 6eb3c3d0a52d ("exec: increase BINPRM_BUF_SIZE to 256") landed, resulting in the tests needing to be refactored for the larger BINPRM_BUF_SIZE, which got lost on my TODO list. During the recent exec refactoring work[1], the need for these tests resurfaced, so I've finished them up for addition to the kernel selftests.
[1] https://lore.kernel.org/lkml/202005191144.E3112135@keescook/
Signed-off-by: Kees Cook keescook@chromium.org --- tools/testing/selftests/exec/Makefile | 1 + tools/testing/selftests/exec/binfmt_script | 171 +++++++++++++++++++++ 2 files changed, 172 insertions(+) create mode 100755 tools/testing/selftests/exec/binfmt_script
diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index 33339e31e365..7f4527f897c4 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -3,6 +3,7 @@ CFLAGS = -Wall 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 diff --git a/tools/testing/selftests/exec/binfmt_script b/tools/testing/selftests/exec/binfmt_script new file mode 100755 index 000000000000..05f94a741c7a --- /dev/null +++ b/tools/testing/selftests/exec/binfmt_script @@ -0,0 +1,171 @@ +#!/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))