coreutils: dummy -> true -> coreutils symlink chain runs as true

docs/src/extensions.md

@@ -25,12 +25,15 @@ $ ls -w=80
 With GNU coreutils, `--help` usually prints the help message and `--version` prints the version.
 We also commonly provide short options: `-h` for help and `-V` for version.
 
-## `coreutils`
+## `coreutils` (multi-call binary)
 
 Our `coreutils` calls utility by `coreutils utility-name` and has `--list` to run against busybox test suite.
 Our `coreutils` is called as `utility-name` if its binary name ends with `utility-name` to support prefixed names.
 Longer name is prioritized e.g. `sum` with the prefix `ck` is called as `cksum`.
 
+On Linux, the symlink chain `dummy` -> `utility-name` -> `coreutils` tries to run `utility-name`
+i.e. `dummy` tries to behave like individual binaries. It is important if `utility-name` is `true`.
+
 ## `env`
 
 GNU `env` allows the empty string to be used as an environment variable name.

src/bin/coreutils.rs

@@ -73,6 +73,18 @@ fn main() {
         // todo: Remove support of "*box" from binary
         uucore::set_utility_is_second_arg();
         args.next()
+    // with the invalid_name -> true -> coreutils symlink chain, run true
+    // this is possible on the platform not using argv0
+    } else if cfg!(any(target_os = "linux", target_os = "android"))
+        && let Ok(binary) = std::fs::read_link(&binary)
+        && let Some(valid) = validation::name(&binary)
+        && !valid.ends_with("utils")
+        && let Some(&matched) = utils
+            .keys()
+            .filter(|&&u| valid.ends_with(u))
+            .max_by_key(|u| u.len())
+    {
+        Some(OsString::from(matched))
     } else {
         validation::not_found(&OsString::from(binary_as_util));
     };

src/common/validation.rs

@@ -94,15 +94,17 @@ pub fn binary_path(args: &mut impl Iterator<Item = OsString>) -> PathBuf {
     let exec_path = Path::new(OsStr::from_bytes(execfn_bytes));
     let argv0 = args.next().unwrap();
     let mut shebang_buf = [0u8; 2];
-    // exec_path is wrong when called from shebang or memfd_create (/proc/self/fd/*)
-    // argv0 is not full-path when called from PATH
     if execfn_bytes.rsplit(|&b| b == b'/').next() == argv0.as_bytes().rsplit(|&b| b == b'/').next()
-        || execfn_bytes.starts_with(b"/proc/")
+    {
+        // argv0 is not full-path when called from PATH
+        exec_path.into()
+    } else if execfn_bytes.starts_with(b"/proc/")
         || (File::open(Path::new(exec_path))
             .and_then(|mut f| f.read_exact(&mut shebang_buf))
             .is_ok()
             && &shebang_buf == b"#!")
     {
+        // exec_path is wrong when called from shebang or memfd_create (/proc/self/fd/*)
         argv0.into()
     } else {
         exec_path.into()

tests/test_util_name.rs

@@ -26,6 +26,22 @@ fn init() {
     eprintln!("Setting UUTESTS_BINARY_PATH={TESTS_BINARY}");
 }
 
+#[test]
+#[cfg(all(feature = "env", any(target_os = "linux", target_os = "android")))]
+fn binary_name_symlink_chain() {
+    let ts = TestScenario::new("chain");
+    let core_path = &ts.bin_path;
+    let env_path = ts.fixtures.plus("prefixed-env");
+    let dummy_path = ts.fixtures.plus("dummy");
+    symlink_file(core_path, &env_path).unwrap();
+    symlink_file(&env_path, &dummy_path).unwrap();
+    let is_env = std::process::Command::new(&dummy_path)
+        .status()
+        .unwrap()
+        .success();
+    assert!(is_env, "symlink chain dummy -> env -> coreutils failed");
+}
+
 #[test]
 #[cfg(all(feature = "env", any(target_os = "linux", target_os = "android")))]
 fn binary_name_protection() {