coreutils: Protect against env -a for security (#10773)

This prevents an attacker from spoofing argv[0] to bypass apparmor restrictions.

- `env -a false ls` now correctly runs `ls` instead of dispatching as `false`
- Also works under masked `/proc` (does not rely on /proc/self/exe).

Closes #10135

.vscode/cspell.dictionaries/workspace.wordlist.txt

@@ -366,6 +366,7 @@ uutests
 uutils
 
 # * function names
+execfn
 getcwd
 setpipe
 

Cargo.lock

@@ -576,6 +576,7 @@ dependencies = [
  "rstest",
  "rstest_reuse",
  "rustc-hash",
+ "rustix",
  "selinux",
  "sha1",
  "tempfile",

Cargo.toml

@@ -1,7 +1,7 @@
 # coreutils (uutils)
 # * see the repository LICENSE, README, and CONTRIBUTING files for more information
 
-# spell-checker:ignore (libs) bigdecimal datetime foldhash serde gethostid kqueue libselinux mangen memmap uuhelp startswith constness expl unnested logind cfgs interner
+# spell-checker:ignore (libs) bigdecimal datetime foldhash serde gethostid kqueue libselinux mangen memmap uuhelp startswith constness expl unnested logind cfgs interner getauxval
 
 [package]
 name = "coreutils"
@@ -454,7 +454,9 @@ rstest = "0.26.0"
 rstest_reuse = "0.7.0"
 rustc-hash = "2.1.1"
 rust-ini = "0.21.0"
-rustix = "1.1.4"
+# binary name of coreutils can be hijacked by overriding getauxval via LD_PRELOAD
+# So we use param and avoid libc backend
+rustix = { version = "1.1.4", features = ["param"] }
 same-file = "1.0.6"
 self_cell = "1.0.4"
 selinux = "=0.6.0"
@@ -624,6 +626,9 @@ who = { optional = true, version = "0.8.0", package = "uu_who", path = "src/uu/w
 whoami = { optional = true, version = "0.8.0", package = "uu_whoami", path = "src/uu/whoami" }
 yes = { optional = true, version = "0.8.0", package = "uu_yes", path = "src/uu/yes" }
 
+[target.'cfg(any(target_os = "linux", target_os = "android"))'.dependencies]
+rustix.workspace = true
+
 # this breaks clippy linting with: "tests/by-util/test_factor_benches.rs: No such file or directory (os error 2)"
 # factor_benches = { optional = true, version = "0.0.0", package = "uu_factor_benches", path = "tests/benches/factor" }
 

src/common/validation.rs

@@ -3,7 +3,7 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// spell-checker:ignore prefixcat testcat
+// spell-checker:ignore memfd_create prefixcat rsplit testcat
 
 use std::ffi::{OsStr, OsString};
 use std::io::{Write, stderr};
@@ -73,15 +73,41 @@ fn get_canonical_util_name(util_name: &str) -> &str {
 }
 
 /// Gets the binary path from command line arguments
-/// # Panics
 /// Panics if the binary path cannot be determined
+#[cfg(not(any(target_os = "linux", target_os = "android")))]
 pub fn binary_path(args: &mut impl Iterator<Item = OsString>) -> PathBuf {
     match args.next() {
         Some(ref s) if !s.is_empty() => PathBuf::from(s),
+        // the fallback is valid only for hardlinks
         _ => std::env::current_exe().unwrap(),
     }
 }
-
+/// Get actual binary path from kernel, not argv0, to prevent `env -a` from bypassing
+/// AppArmor, SELinux policies on hard-linked binaries
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub fn binary_path(args: &mut impl Iterator<Item = OsString>) -> PathBuf {
+    use std::fs::File;
+    use std::io::Read;
+    use std::os::unix::ffi::OsStrExt;
+    let execfn = rustix::param::linux_execfn();
+    let execfn_bytes = execfn.to_bytes();
+    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/")
+        || (File::open(Path::new(exec_path))
+            .and_then(|mut f| f.read_exact(&mut shebang_buf))
+            .is_ok()
+            && &shebang_buf == b"#!")
+    {
+        argv0.into()
+    } else {
+        exec_path.into()
+    }
+}
 /// Extracts the binary name from a path
 pub fn name(binary_path: &Path) -> Option<&str> {
     binary_path.file_stem()?.to_str()

tests/test_util_name.rs

@@ -26,6 +26,20 @@ fn init() {
     eprintln!("Setting UUTESTS_BINARY_PATH={TESTS_BINARY}");
 }
 
+#[test]
+#[cfg(all(feature = "env", any(target_os = "linux", target_os = "android")))]
+fn binary_name_protection() {
+    let ts = TestScenario::new("env");
+    let bin = ts.bin_path.clone();
+    ts.ucmd()
+        .arg("-a")
+        .arg("hijacked")
+        .arg(&bin)
+        .arg("--version")
+        .succeeds()
+        .stdout_contains("coreutils");
+}
+
 #[test]
 #[cfg(feature = "ls")]
 fn execution_phrase_double() {