git, branch v2.30.6

Git 2.30.6

2022-10-06T21:38:16Z

Signed-off-by: Taylor Blau

alias.c: reject too-long cmdline strings in split_cmdline()

2022-10-01T04:23:38Z

This function improperly uses an int to represent the number of entries in the resulting argument array. This allows a malicious actor to intentionally overflow the return value, leading to arbitrary heap writes. Because the resulting argv array is typically passed to execv(), it may be possible to leverage this attack to gain remote code execution on a victim machine. This was almost certainly the case for certain configurations of git-shell until the previous commit limited the size of input it would accept. Other calls to split_cmdline() are typically limited by the size of argv the OS is willing to hand us, so are similarly protected. So this is not strictly fixing a known vulnerability, but is a hardening of the function that is worth doing to protect against possible unknown vulnerabilities. One approach to fixing this would be modifying the signature of `split_cmdline()` to look something like: int split_cmdline(char *cmdline, const char ***argv, size_t *argc); Where the return value of `split_cmdline()` is negative for errors, and zero otherwise. If non-NULL, the `*argc` pointer is modified to contain the size of the `**argv` array. But this implies an absurdly large `argv` array, which more than likely larger than the system's argument limit. So even if split_cmdline() allowed this, it would fail immediately afterwards when we called execv(). So instead of converting all of `split_cmdline()`'s callers to work with `size_t` types in this patch, instead pursue the minimal fix here to prevent ever returning an array with more than INT_MAX entries in it. Signed-off-by: Kevin Backhouse Signed-off-by: Taylor Blau Signed-off-by: Jeff King Signed-off-by: Taylor Blau

shell: limit size of interactive commands

2022-10-01T04:23:38Z

When git-shell is run in interactive mode (which must be enabled by creating $HOME/git-shell-commands), it reads commands from stdin, one per line, and executes them. We read the commands with git_read_line_interactively(), which uses a strbuf under the hood. That means we'll accept an input of arbitrary size (limited only by how much heap we can allocate). That creates two problems: - the rest of the code is not prepared to handle large inputs. The most serious issue here is that split_cmdline() uses "int" for most of its types, which can lead to integer overflow and out-of-bounds array reads and writes. But even with that fixed, we assume that we can feed the command name to snprintf() (via xstrfmt()), which is stuck for historical reasons using "int", and causes it to fail (and even trigger a BUG() call). - since the point of git-shell is to take input from untrusted or semi-trusted clients, it's a mild denial-of-service. We'll allocate as many bytes as the client sends us (actually twice as many, since we immediately duplicate the buffer). We can fix both by just limiting the amount of per-command input we're willing to receive. We should also fix split_cmdline(), of course, which is an accident waiting to happen, but that can come on top. Most calls to split_cmdline(), including the other one in git-shell, are OK because they are reading from an OS-provided argv, which is limited in practice. This patch should eliminate the immediate vulnerabilities. I picked 4MB as an arbitrary limit. It's big enough that nobody should ever run into it in practice (since the point is to run the commands via exec, we're subject to OS limits which are typically much lower). But it's small enough that allocating it isn't that big a deal. The code is mostly just swapping out fgets() for the strbuf call, but we have to add a few niceties like flushing and trimming line endings. We could simplify things further by putting the buffer on the stack, but 4MB is probably a bit much there. Note that we'll _always_ allocate 4MB, which for normal, non-malicious requests is more than we would before this patch. But on the other hand, other git programs are happy to use 96MB for a delta cache. And since we'd never touch most of those pages, on a lazy-allocating OS like Linux they won't even get allocated to actual RAM. The ideal would be a version of strbuf_getline() that accepted a maximum value. But for a minimal vulnerability fix, let's keep things localized and simple. We can always refactor further on top. The included test fails in an obvious way with ASan or UBSan (which notice the integer overflow and out-of-bounds reads). Without them, it fails in a less obvious way: we may segfault, or we may try to xstrfmt() a long string, leading to a BUG(). Either way, it fails reliably before this patch, and passes with it. Note that we don't need an EXPENSIVE prereq on it. It does take 10-15s to fail before this patch, but with the new limit, we fail almost immediately (and the perl process generating 2GB of data exits via SIGPIPE). Signed-off-by: Jeff King Signed-off-by: Taylor Blau

shell: add basic tests

2022-10-01T04:23:38Z

We have no tests of even basic functionality of git-shell. Let's add a couple of obvious ones. This will serve as a framework for adding tests for new things we fix, as well as making sure we don't screw anything up too badly while doing so. Signed-off-by: Jeff King Signed-off-by: Taylor Blau

transport: make `protocol.file.allow` be "user" by default

2022-10-01T04:23:38Z

An earlier patch discussed and fixed a scenario where Git could be used as a vector to exfiltrate sensitive data through a Docker container when a potential victim clones a suspicious repository with local submodules that contain symlinks. That security hole has since been plugged, but a similar one still exists. Instead of convincing a would-be victim to clone an embedded submodule via the "file" protocol, an attacker could convince an individual to clone a repository that has a submodule pointing to a valid path on the victim's filesystem. For example, if an individual (with username "foo") has their home directory ("/home/foo") stored as a Git repository, then an attacker could exfiltrate data by convincing a victim to clone a malicious repository containing a submodule pointing at "/home/foo/.git" with `--recurse-submodules`. Doing so would expose any sensitive contents in stored in "/home/foo" tracked in Git. For systems (such as Docker) that consider everything outside of the immediate top-level working directory containing a Dockerfile as inaccessible to the container (with the exception of volume mounts, and so on), this is a violation of trust by exposing unexpected contents in the working copy. To mitigate the likelihood of this kind of attack, adjust the "file://" protocol's default policy to be "user" to prevent commands that execute without user input (including recursive submodule initialization) from taking place by default. Suggested-by: Jeff King Signed-off-by: Taylor Blau

t/t9NNN: allow local submodules

2022-10-01T04:23:38Z

To prepare for the default value of `protocol.file.allow` to change to "user", ensure tests that rely on local submodules can initialize them over the file protocol. Tests that interact with submodules a handful of times use `test_config_global`. Signed-off-by: Taylor Blau

t/t7NNN: allow local submodules

2022-10-01T04:23:38Z

To prepare for the default value of `protocol.file.allow` to change to "user", ensure tests that rely on local submodules can initialize them over the file protocol. Tests that only need to interact with submodules in a limited capacity have individual Git commands annotated with the appropriate configuration via `-c`. Tests that interact with submodules a handful of times use `test_config_global` instead. Test scripts that rely on submodules throughout use a `git config --global` during a setup test towards the beginning of the script. Signed-off-by: Taylor Blau

t/t6NNN: allow local submodules

2022-10-01T04:23:38Z

t/t5NNN: allow local submodules

2022-10-01T04:23:38Z

t/t4NNN: allow local submodules

2022-10-01T04:23:38Z