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authorJohannes Schindelin <johannes.schindelin@gmx.de>2022-03-02 11:23:04 (GMT)
committerJohannes Schindelin <johannes.schindelin@gmx.de>2022-03-21 12:16:26 (GMT)
commit8959555cee7ec045958f9b6dd62e541affb7e7d9 (patch)
treeda189c139989e8ea73421bde49a076ae9508661b
parentbdc77d1d685be9c10b88abb281a42bc620548595 (diff)
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setup_git_directory(): add an owner check for the top-level directory
It poses a security risk to search for a git directory outside of the directories owned by the current user. For example, it is common e.g. in computer pools of educational institutes to have a "scratch" space: a mounted disk with plenty of space that is regularly swiped where any authenticated user can create a directory to do their work. Merely navigating to such a space with a Git-enabled `PS1` when there is a maliciously-crafted `/scratch/.git/` can lead to a compromised account. The same holds true in multi-user setups running Windows, as `C:\` is writable to every authenticated user by default. To plug this vulnerability, we stop Git from accepting top-level directories owned by someone other than the current user. We avoid looking at the ownership of each and every directories between the current and the top-level one (if there are any between) to avoid introducing a performance bottleneck. This new default behavior is obviously incompatible with the concept of shared repositories, where we expect the top-level directory to be owned by only one of its legitimate users. To re-enable that use case, we add support for adding exceptions from the new default behavior via the config setting `safe.directory`. The `safe.directory` config setting is only respected in the system and global configs, not from repository configs or via the command-line, and can have multiple values to allow for multiple shared repositories. We are particularly careful to provide a helpful message to any user trying to use a shared repository. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
-rw-r--r--Documentation/config.txt2
-rw-r--r--Documentation/config/safe.txt21
-rw-r--r--setup.c57
3 files changed, 79 insertions, 1 deletions
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 6ba50b1..34e6d47 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -438,6 +438,8 @@ include::config/rerere.txt[]
include::config/reset.txt[]
+include::config/safe.txt[]
+
include::config/sendemail.txt[]
include::config/sequencer.txt[]
diff --git a/Documentation/config/safe.txt b/Documentation/config/safe.txt
new file mode 100644
index 0000000..63597b2
--- /dev/null
+++ b/Documentation/config/safe.txt
@@ -0,0 +1,21 @@
+safe.directory::
+ These config entries specify Git-tracked directories that are
+ considered safe even if they are owned by someone other than the
+ current user. By default, Git will refuse to even parse a Git
+ config of a repository owned by someone else, let alone run its
+ hooks, and this config setting allows users to specify exceptions,
+ e.g. for intentionally shared repositories (see the `--shared`
+ option in linkgit:git-init[1]).
++
+This is a multi-valued setting, i.e. you can add more than one directory
+via `git config --add`. To reset the list of safe directories (e.g. to
+override any such directories specified in the system config), add a
+`safe.directory` entry with an empty value.
++
+This config setting is only respected when specified in a system or global
+config, not when it is specified in a repository config or via the command
+line option `-c safe.directory=<path>`.
++
+The value of this setting is interpolated, i.e. `~/<path>` expands to a
+path relative to the home directory and `%(prefix)/<path>` expands to a
+path relative to Git's (runtime) prefix.
diff --git a/setup.c b/setup.c
index c04cd25..95d5b00 100644
--- a/setup.c
+++ b/setup.c
@@ -5,6 +5,7 @@
#include "string-list.h"
#include "chdir-notify.h"
#include "promisor-remote.h"
+#include "quote.h"
static int inside_git_dir = -1;
static int inside_work_tree = -1;
@@ -1024,6 +1025,42 @@ static int canonicalize_ceiling_entry(struct string_list_item *item,
}
}
+struct safe_directory_data {
+ const char *path;
+ int is_safe;
+};
+
+static int safe_directory_cb(const char *key, const char *value, void *d)
+{
+ struct safe_directory_data *data = d;
+
+ if (!value || !*value)
+ data->is_safe = 0;
+ else {
+ const char *interpolated = NULL;
+
+ if (!git_config_pathname(&interpolated, key, value) &&
+ !fspathcmp(data->path, interpolated ? interpolated : value))
+ data->is_safe = 1;
+
+ free((char *)interpolated);
+ }
+
+ return 0;
+}
+
+static int ensure_valid_ownership(const char *path)
+{
+ struct safe_directory_data data = { .path = path };
+
+ if (is_path_owned_by_current_user(path))
+ return 1;
+
+ read_very_early_config(safe_directory_cb, &data);
+
+ return data.is_safe;
+}
+
enum discovery_result {
GIT_DIR_NONE = 0,
GIT_DIR_EXPLICIT,
@@ -1032,7 +1069,8 @@ enum discovery_result {
/* these are errors */
GIT_DIR_HIT_CEILING = -1,
GIT_DIR_HIT_MOUNT_POINT = -2,
- GIT_DIR_INVALID_GITFILE = -3
+ GIT_DIR_INVALID_GITFILE = -3,
+ GIT_DIR_INVALID_OWNERSHIP = -4
};
/*
@@ -1122,11 +1160,15 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
}
strbuf_setlen(dir, offset);
if (gitdirenv) {
+ if (!ensure_valid_ownership(dir->buf))
+ return GIT_DIR_INVALID_OWNERSHIP;
strbuf_addstr(gitdir, gitdirenv);
return GIT_DIR_DISCOVERED;
}
if (is_git_directory(dir->buf)) {
+ if (!ensure_valid_ownership(dir->buf))
+ return GIT_DIR_INVALID_OWNERSHIP;
strbuf_addstr(gitdir, ".");
return GIT_DIR_BARE;
}
@@ -1253,6 +1295,19 @@ const char *setup_git_directory_gently(int *nongit_ok)
dir.buf);
*nongit_ok = 1;
break;
+ case GIT_DIR_INVALID_OWNERSHIP:
+ if (!nongit_ok) {
+ struct strbuf quoted = STRBUF_INIT;
+
+ sq_quote_buf_pretty(&quoted, dir.buf);
+ die(_("unsafe repository ('%s' is owned by someone else)\n"
+ "To add an exception for this directory, call:\n"
+ "\n"
+ "\tgit config --global --add safe.directory %s"),
+ dir.buf, quoted.buf);
+ }
+ *nongit_ok = 1;
+ break;
case GIT_DIR_NONE:
/*
* As a safeguard against setup_git_directory_gently_1 returning