Check program paths against entry points in Occlum.json

etc/template/Occlum.json

@@ -10,6 +10,9 @@
     "env": [
         "OCCLUM=yes"
     ],
+    "entry_points": [
+        "/bin"
+    ],
     "mount": [
         {
             "target": "/",

src/libos/src/config.rs

@@ -80,6 +80,7 @@ pub struct Config {
     pub vm: ConfigVM,
     pub process: ConfigProcess,
     pub env: Vec<CString>,
+    pub entry_points: Vec<PathBuf>,
     pub mount: Vec<ConfigMount>,
 }
 
@@ -128,6 +129,17 @@ impl Config {
             }
             env
         };
+        let entry_points = {
+            let mut entry_points = Vec::new();
+            for ep in &input.entry_points {
+                let ep_path = Path::new(ep).to_path_buf();
+                if !ep_path.is_absolute() {
+                    return_errno!(EINVAL, "entry point must be an absolute path")
+                }
+                entry_points.push(ep_path);
+            }
+            entry_points
+        };
         let mount = {
             let mut mount = Vec::new();
             for input_mount in &input.mount {
@@ -139,6 +151,7 @@ impl Config {
             vm,
             process,
             env,
+            entry_points,
             mount,
         })
     }
@@ -246,6 +259,8 @@ struct InputConfig {
     #[serde(default)]
     pub env: Vec<String>,
     #[serde(default)]
+    pub entry_points: Vec<String>,
+    #[serde(default)]
     pub mount: Vec<InputConfigMount>,
 }
 
@@ -269,7 +284,6 @@ impl Default for InputConfigVM {
         }
     }
 }
-
 #[derive(Deserialize, Debug)]
 #[serde(deny_unknown_fields)]
 struct InputConfigProcess {

src/libos/src/entry.rs

@@ -2,7 +2,7 @@ use super::*;
 use exception::*;
 use process::pid_t;
 use std::ffi::{CStr, CString, OsString};
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use util::mem_util::from_untrusted::*;
 
 const ENCLAVE_PATH: &'static str = ".occlum/build/lib/libocclum.signed.so";
@@ -60,15 +60,18 @@ pub extern "C" fn dummy_ecall() -> i32 {
 const EXIT_STATUS_INTERNAL_ERROR: i32 = 127;
 
 fn parse_arguments(
-    path_buf: *const c_char,
+    path_ptr: *const c_char,
     argv: *const *const c_char,
-) -> Result<(String, Vec<CString>)> {
-    let path_string = {
-        let path_cstring = clone_cstring_safely(path_buf)?;
-        path_cstring.to_string_lossy().into_owned()
+) -> Result<(PathBuf, Vec<CString>)> {
+    let path_buf = {
+        let path_cstring = clone_cstring_safely(path_ptr)?;
+        let path_string = path_cstring
+            .into_string()
+            .map_err(|e| errno!(EINVAL, "path contains valid utf-8 data"))?;
+        Path::new(&path_string).to_path_buf()
     };
     let program_cstring = {
-        let program_osstr = Path::new(&path_string)
+        let program_osstr = path_buf
             .file_name()
             .ok_or_else(|| errno!(EINVAL, "invalid path"))?;
         let program_str = program_osstr
@@ -79,18 +82,20 @@ fn parse_arguments(
 
     let mut args = clone_cstrings_safely(argv)?;
     args.insert(0, program_cstring);
-    Ok((path_string, args))
+    Ok((path_buf, args))
 }
 
 // TODO: make sure do_boot can only be called once
-fn do_boot(path_str: &str, argv: &Vec<CString>) -> Result<()> {
+fn do_boot(program_path: &PathBuf, argv: &Vec<CString>) -> Result<()> {
     //    info!("boot: path: {:?}, argv: {:?}", path_str, argv);
     util::mpx_util::mpx_enable()?;
 
+    validate_program_path(program_path)?;
+
     let envp = &config::LIBOS_CONFIG.env;
     let file_actions = Vec::new();
     let parent = &process::IDLE_PROCESS;
-    process::do_spawn(&path_str, argv, envp, &file_actions, parent)?;
+    process::do_spawn(&program_path, argv, envp, &file_actions, parent)?;
 
     Ok(())
 }
@@ -106,3 +111,32 @@ fn do_run(host_tid: pid_t) -> Result<i32> {
 
     Ok(exit_status)
 }
+
+fn validate_program_path(target_path: &PathBuf) -> Result<()> {
+    if !target_path.is_absolute() {
+        return_errno!(EINVAL, "program path must be absolute");
+    }
+
+    // Forbid paths like /bin/../root, which may circument our prefix-based path matching
+    let has_parent_component = {
+        target_path
+            .components()
+            .any(|component| component == std::path::Component::ParentDir)
+    };
+    if has_parent_component {
+        return_errno!(
+            EINVAL,
+            "program path cannot contain any parent component (i.e., \"..\")"
+        );
+    }
+
+    // Check whether the prefix of the program path matches one of the entry points
+    let is_valid_entry_point = &config::LIBOS_CONFIG
+        .entry_points
+        .iter()
+        .any(|valid_path_prefix| target_path.starts_with(valid_path_prefix));
+    if !is_valid_entry_point {
+        return_errno!(EINVAL, "program path is a valid entry point");
+    }
+    Ok(())
+}

test/Occlum.json

@@ -11,6 +11,9 @@
         "OCCLUM=yes",
         "TEST=true"
     ],
+    "entry_points": [
+        "/bin"
+    ],
     "mount": [
         {
             "target": "/",

tools/occlum

@@ -52,6 +52,11 @@ get_conf_env() {
         python -c "import sys, json; print json.dumps(json.load(sys.stdin)['env'])"
 }
 
+get_conf_entry_points() {
+    cat "$working_dir/Occlum.json" | \
+        python -c "import sys, json; print json.dumps(json.load(sys.stdin)['entry_points'])"
+}
+
 get_occlum_conf_file_mac() {
     "$occlum_dir/build/bin/occlum-protect-integrity" show-mac "$context_dir/build/Occlum.json.protected"
 }
@@ -78,7 +83,7 @@ cmd_init() {
 
     local occlum_gcc_lib=/usr/local/occlum/x86_64-linux-musl/lib
     cp -t image/lib/ \
-    	/lib/ld-musl-x86_64.so.1 \
+        /lib/ld-musl-x86_64.so.1 \
         "$occlum_gcc_lib/libc.so" \
         "$occlum_gcc_lib/libstdc++.so.6" \
         "$occlum_gcc_lib/libgcc_s.so.1" \
@@ -121,6 +126,7 @@ cmd_build() {
     export OCCLUM_CONF_DEFAULT_HEAP_SIZE=`get_conf_default_heap_size`
     export OCCLUM_CONF_DEFAULT_MMAP_SIZE=`get_conf_default_mmap_size`
     export OCCLUM_CONF_ENV=`get_conf_env`
+    export OCCLUM_CONF_ENTRY_POINTS=`get_conf_entry_points`
     cd "$context_dir/build"
     "$occlum_dir/build/bin/occlum-gen-default-occlum-json"\
         > "Occlum.json"

tools/occlum-gen-default-occlum-json

@@ -34,6 +34,7 @@ cat <<EOF
             "type": "ramfs"
         }
     ],
-    "env": $OCCLUM_CONF_ENV
+    "env": $OCCLUM_CONF_ENV,
+    "entry_points": $OCCLUM_CONF_ENTRY_POINTS
 }
 EOF