Sketch Permissions for git-config (#386)

It should be possible to control which configuration files are loaded
and contribute to the overall configuration. This goes along with
at some point allowing to obtain only values which are from trusted
configuration files, based on the trust specification passed when
loading the configuration.

Author: Byron

Cargo.lock

@@ -15,6 +15,8 @@ include = ["src/**/*", "LICENSE-*", "README.md", "CHANGELOG.md"]
 
 [dependencies]
 git-features = { version = "^0.20.0", path = "../git-features"}
+git-sec = { version = "^0.1.0", path = "../git-sec" }
+
 dirs = "4"
 nom = { version = "7", default_features = false, features = [ "std" ] }
 memchr = "2"

git-config/Cargo.toml

@@ -59,12 +59,65 @@ pub mod fs;
 pub mod parser;
 pub mod values;
 
-// mod de;
-// mod ser;
-// mod error;
-// pub use de::{from_str, Deserializer};
-// pub use error::{Error, Result};
-// pub use ser::{to_string, Serializer};
+mod permissions {
+    use crate::Permissions;
+
+    impl Permissions {
+        /// Allow everything which usually relates to a fully trusted environment
+        pub fn all() -> Self {
+            use git_sec::Permission::*;
+            Permissions {
+                system: Allow,
+                global: Allow,
+                user: Allow,
+                repository: Allow,
+                worktree: Allow,
+                env: Allow,
+                includes: Allow,
+            }
+        }
+
+        /// If in doubt, this configuration can be used to safely load configuration from sources which is usually trusted,
+        /// that is system and user configuration. Do load any configuration that isn't trusted as it's now owned by the current user.
+        pub fn secure() -> Self {
+            use git_sec::Permission::*;
+            Permissions {
+                system: Allow,
+                global: Allow,
+                user: Allow,
+                repository: Deny,
+                worktree: Deny,
+                env: Allow,
+                includes: Deny,
+            }
+        }
+    }
+}
+
+/// Configure security relevant options when loading a git configuration.
+#[derive(Copy, Clone, Ord, PartialOrd, PartialEq, Eq, Debug, Hash)]
+#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
+pub struct Permissions {
+    /// How to use the system configuration.
+    /// This is defined as `$(prefix)/etc/gitconfig` on unix.
+    pub system: git_sec::Permission,
+    /// How to use the global configuration.
+    /// This is usually `~/.gitconfig`.
+    pub global: git_sec::Permission,
+    /// How to use the user configuration.
+    /// Second user-specific configuration path; if `$XDG_CONFIG_HOME` is not
+    /// set or empty, `$HOME/.config/git/config` will be used.
+    pub user: git_sec::Permission,
+    /// How to use the repository configuration.
+    pub repository: git_sec::Permission,
+    /// How to use worktree configuration from `config.worktree`.
+    // TODO: figure out how this really applies and provide more information here.
+    pub worktree: git_sec::Permission,
+    /// How to use the configuration from environment variables.
+    pub env: git_sec::Permission,
+    /// What to do when include files are encountered in loaded configuration.
+    pub includes: git_sec::Permission,
+}
 
 #[cfg(test)]
 pub mod test_util;