git/t/t7415-submodule-names.sh

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submodule-config: verify submodule names as paths Submodule "names" come from the untrusted .gitmodules file, but we blindly append them to $GIT_DIR/modules to create our on-disk repo paths. This means you can do bad things by putting "../" into the name (among other things). Let's sanity-check these names to avoid building a path that can be exploited. There are two main decisions: 1. What should the allowed syntax be? It's tempting to reuse verify_path(), since submodule names typically come from in-repo paths. But there are two reasons not to: a. It's technically more strict than what we need, as we really care only about breaking out of the $GIT_DIR/modules/ hierarchy. E.g., having a submodule named "foo/.git" isn't actually dangerous, and it's possible that somebody has manually given such a funny name. b. Since we'll eventually use this checking logic in fsck to prevent downstream repositories, it should be consistent across platforms. Because verify_path() relies on is_dir_sep(), it wouldn't block "foo\..\bar" on a non-Windows machine. 2. Where should we enforce it? These days most of the .gitmodules reads go through submodule-config.c, so I've put it there in the reading step. That should cover all of the C code. We also construct the name for "git submodule add" inside the git-submodule.sh script. This is probably not a big deal for security since the name is coming from the user anyway, but it would be polite to remind them if the name they pick is invalid (and we need to expose the name-checker to the shell anyway for our test scripts). This patch issues a warning when reading .gitmodules and just ignores the related config entry completely. This will generally end up producing a sensible error, as it works the same as a .gitmodules file which is missing a submodule entry (so "submodule update" will barf, but "git clone --recurse-submodules" will print an error but not abort the clone. There is one minor oddity, which is that we print the warning once per malformed config key (since that's how the config subsystem gives us the entries). So in the new test, for example, the user would see three warnings. That's OK, since the intent is that this case should never come up outside of malicious repositories (and then it might even benefit the user to see the message multiple times). Credit for finding this vulnerability and the proof of concept from which the test script was adapted goes to Etienne Stalmans. Signed-off-by: Jeff King <peff@peff.net>
2018-04-30 07:25:25 +00:00
#!/bin/sh
test_description='check handling of .. in submodule names
Exercise the name-checking function on a variety of names, and then give a
real-world setup that confirms we catch this in practice.
'
. ./test-lib.sh
test_expect_success 'check names' '
cat >expect <<-\EOF &&
valid
valid/with/paths
EOF
git submodule--helper check-name >actual <<-\EOF &&
valid
valid/with/paths
../foo
/../foo
..\foo
\..\foo
foo/..
foo/../
foo\..
foo\..\
foo/../bar
EOF
test_cmp expect actual
'
test_expect_success 'create innocent subrepo' '
git init innocent &&
git -C innocent commit --allow-empty -m foo
'
test_expect_success 'submodule add refuses invalid names' '
test_must_fail \
git submodule add --name ../../modules/evil "$PWD/innocent" evil
'
test_expect_success 'add evil submodule' '
git submodule add "$PWD/innocent" evil &&
mkdir modules &&
cp -r .git/modules/evil modules &&
write_script modules/evil/hooks/post-checkout <<-\EOF &&
echo >&2 "RUNNING POST CHECKOUT"
EOF
git config -f .gitmodules submodule.evil.update checkout &&
git config -f .gitmodules --rename-section \
submodule.evil submodule.../../modules/evil &&
git add modules &&
git commit -am evil
'
# This step seems like it shouldn't be necessary, since the payload is
# contained entirely in the evil submodule. But due to the vagaries of the
# submodule code, checking out the evil module will fail unless ".git/modules"
# exists. Adding another submodule (with a name that sorts before "evil") is an
# easy way to make sure this is the case in the victim clone.
test_expect_success 'add other submodule' '
git submodule add "$PWD/innocent" another-module &&
git add another-module &&
git commit -am another
'
test_expect_success 'clone evil superproject' '
git clone --recurse-submodules . victim >output 2>&1 &&
! grep "RUNNING POST CHECKOUT" output
'
clone --recurse-submodules: prevent name squatting on Windows In addition to preventing `.git` from being tracked by Git, on Windows we also have to prevent `git~1` from being tracked, as the default NTFS short name (also known as the "8.3 filename") for the file name `.git` is `git~1`, otherwise it would be possible for malicious repositories to write directly into the `.git/` directory, e.g. a `post-checkout` hook that would then be executed _during_ a recursive clone. When we implemented appropriate protections in 2b4c6efc821 (read-cache: optionally disallow NTFS .git variants, 2014-12-16), we had analyzed carefully that the `.git` directory or file would be guaranteed to be the first directory entry to be written. Otherwise it would be possible e.g. for a file named `..git` to be assigned the short name `git~1` and subsequently, the short name generated for `.git` would be `git~2`. Or `git~3`. Or even `~9999999` (for a detailed explanation of the lengths we have to go to protect `.gitmodules`, see the commit message of e7cb0b4455c (is_ntfs_dotgit: match other .git files, 2018-05-11)). However, by exploiting two issues (that will be addressed in a related patch series close by), it is currently possible to clone a submodule into a non-empty directory: - On Windows, file names cannot end in a space or a period (for historical reasons: the period separating the base name from the file extension was not actually written to disk, and the base name/file extension was space-padded to the full 8/3 characters, respectively). Helpfully, when creating a directory under the name, say, `sub.`, that trailing period is trimmed automatically and the actual name on disk is `sub`. This means that while Git thinks that the submodule names `sub` and `sub.` are different, they both access `.git/modules/sub/`. - While the backslash character is a valid file name character on Linux, it is not so on Windows. As Git tries to be cross-platform, it therefore allows backslash characters in the file names stored in tree objects. Which means that it is totally possible that a submodule `c` sits next to a file `c\..git`, and on Windows, during recursive clone a file called `..git` will be written into `c/`, of course _before_ the submodule is cloned. Note that the actual exploit is not quite as simple as having a submodule `c` next to a file `c\..git`, as we have to make sure that the directory `.git/modules/b` already exists when the submodule is checked out, otherwise a different code path is taken in `module_clone()` that does _not_ allow a non-empty submodule directory to exist already. Even if we will address both issues nearby (the next commit will disallow backslash characters in tree entries' file names on Windows, and another patch will disallow creating directories/files with trailing spaces or periods), it is a wise idea to defend in depth against this sort of attack vector: when submodules are cloned recursively, we now _require_ the directory to be empty, addressing CVE-2019-1349. Note: the code path we patch is shared with the code path of `git submodule update --init`, which must not expect, in general, that the directory is empty. Hence we have to introduce the new option `--force-init` and hand it all the way down from `git submodule` to the actual `git submodule--helper` process that performs the initial clone. Reported-by: Nicolas Joly <Nicolas.Joly@microsoft.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
2019-09-12 12:20:39 +00:00
test_expect_success MINGW 'prevent git~1 squatting on Windows' '
git init squatting &&
(
cd squatting &&
mkdir a &&
touch a/..git &&
git add a/..git &&
test_tick &&
git commit -m initial &&
modules="$(test_write_lines \
"[submodule \"b.\"]" "url = ." "path = c" \
"[submodule \"b\"]" "url = ." "path = d\\\\a" |
git hash-object -w --stdin)" &&
rev="$(git rev-parse --verify HEAD)" &&
hash="$(echo x | git hash-object -w --stdin)" &&
git update-index --add \
--cacheinfo 100644,$modules,.gitmodules \
--cacheinfo 160000,$rev,c \
--cacheinfo 160000,$rev,d\\a \
--cacheinfo 100644,$hash,d./a/x \
--cacheinfo 100644,$hash,d./a/..git &&
test_tick &&
git commit -m "module"
) &&
test_must_fail git \
clone --recurse-submodules squatting squatting-clone 2>err &&
test_i18ngrep "directory not empty" err &&
! grep gitdir squatting-clone/d/a/git~2
'
submodule-config: verify submodule names as paths Submodule "names" come from the untrusted .gitmodules file, but we blindly append them to $GIT_DIR/modules to create our on-disk repo paths. This means you can do bad things by putting "../" into the name (among other things). Let's sanity-check these names to avoid building a path that can be exploited. There are two main decisions: 1. What should the allowed syntax be? It's tempting to reuse verify_path(), since submodule names typically come from in-repo paths. But there are two reasons not to: a. It's technically more strict than what we need, as we really care only about breaking out of the $GIT_DIR/modules/ hierarchy. E.g., having a submodule named "foo/.git" isn't actually dangerous, and it's possible that somebody has manually given such a funny name. b. Since we'll eventually use this checking logic in fsck to prevent downstream repositories, it should be consistent across platforms. Because verify_path() relies on is_dir_sep(), it wouldn't block "foo\..\bar" on a non-Windows machine. 2. Where should we enforce it? These days most of the .gitmodules reads go through submodule-config.c, so I've put it there in the reading step. That should cover all of the C code. We also construct the name for "git submodule add" inside the git-submodule.sh script. This is probably not a big deal for security since the name is coming from the user anyway, but it would be polite to remind them if the name they pick is invalid (and we need to expose the name-checker to the shell anyway for our test scripts). This patch issues a warning when reading .gitmodules and just ignores the related config entry completely. This will generally end up producing a sensible error, as it works the same as a .gitmodules file which is missing a submodule entry (so "submodule update" will barf, but "git clone --recurse-submodules" will print an error but not abort the clone. There is one minor oddity, which is that we print the warning once per malformed config key (since that's how the config subsystem gives us the entries). So in the new test, for example, the user would see three warnings. That's OK, since the intent is that this case should never come up outside of malicious repositories (and then it might even benefit the user to see the message multiple times). Credit for finding this vulnerability and the proof of concept from which the test script was adapted goes to Etienne Stalmans. Signed-off-by: Jeff King <peff@peff.net>
2018-04-30 07:25:25 +00:00
test_done