Add Command::resolve_in_parent_path

Author: ChrisDenton

library/std/src/process.rs

@@ -1195,6 +1195,22 @@ impl Command {
     pub fn get_current_dir(&self) -> Option<&Path> {
         self.inner.get_current_dir()
     }
+
+    /// Resolve the program given in [`new`](Self::new) using the parent's PATH.
+    ///
+    /// Usually when a `env` is used to set `PATH` on a child process,
+    /// that new `PATH` will be used to discover the process.
+    /// With `resolve_in_parent_path` to `true`, the parent's `PATH` will be used instead.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// On Unix the process is executed after fork and after setting up the rest of the new environment.
+    /// So if `chroot`, `uid`, `gid` or `groups` are used then the way `PATH` is interpreted may be changed.
+    #[unstable(feature = "command_resolve", issue = "none")]
+    pub fn resolve_in_parent_path(&mut self, use_parent: bool) -> &mut Self {
+        self.inner.resolve_in_parent_path(use_parent);
+        self
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

library/std/src/process/tests.rs

@@ -2,10 +2,10 @@ use super::{Command, Output, Stdio};
 use crate::io::prelude::*;
 use crate::io::{BorrowedBuf, ErrorKind};
 use crate::mem::MaybeUninit;
-use crate::str;
+use crate::{fs, str};
 
 fn known_command() -> Command {
-    if cfg!(windows) { Command::new("help") } else { Command::new("echo") }
+    if cfg!(windows) { Command::new("help.exe") } else { Command::new("echo") }
 }
 
 #[cfg(target_os = "android")]
@@ -603,3 +603,42 @@ fn terminate_exited_process() {
     assert!(p.kill().is_ok());
     assert!(p.kill().is_ok());
 }
+
+#[test]
+fn resolve_in_parent_path() {
+    let tempdir = crate::test_helpers::tmpdir();
+    let mut cmd = if cfg!(windows) {
+        // On Windows std prepends the system paths when searching for executables
+        // but not if PATH is set on the command. Therefore adding a broken exe
+        // using PATH will cause spawn to fail if it's invoked.
+        let mut cmd = known_command();
+        fs::write(tempdir.join(cmd.get_program().to_str().unwrap()), "").unwrap();
+        cmd.env("PATH", tempdir.path());
+        cmd
+    } else {
+        let mut cmd = known_command();
+        cmd.env("PATH", "");
+        cmd
+    };
+
+    assert!(cmd.spawn().is_err());
+    cmd.resolve_in_parent_path(true);
+    assert!(cmd.status().unwrap().success());
+    cmd.resolve_in_parent_path(false);
+    assert!(cmd.spawn().is_err());
+
+    // If the platform is a unix and has posix_spawn then that will be used in the test above.
+    // So we also test the fork/exec path by setting a pre_exec function.
+    #[cfg(unix)]
+    {
+        use crate::os::unix::process::CommandExt;
+        unsafe {
+            cmd.pre_exec(|| Ok(()));
+        }
+        assert!(cmd.spawn().is_err());
+        cmd.resolve_in_parent_path(true);
+        assert!(cmd.status().unwrap().success());
+        cmd.resolve_in_parent_path(false);
+        assert!(cmd.spawn().is_err());
+    }
+}

library/std/src/sys/process/unix/common.rs

@@ -98,6 +98,7 @@ pub struct Command {
     #[cfg(target_os = "linux")]
     create_pidfd: bool,
     pgroup: Option<pid_t>,
+    resolve_in_parent_path: bool,
 }
 
 // passed back to std::process with the pipes connected to the child, if any
@@ -185,6 +186,7 @@ impl Command {
             #[cfg(target_os = "linux")]
             create_pidfd: false,
             pgroup: None,
+            resolve_in_parent_path: false,
         }
     }
 
@@ -220,6 +222,9 @@ impl Command {
             self.cwd(&OsStr::new("/"));
         }
     }
+    pub fn resolve_in_parent_path(&mut self, use_parent: bool) {
+        self.resolve_in_parent_path = use_parent;
+    }
 
     #[cfg(target_os = "linux")]
     pub fn create_pidfd(&mut self, val: bool) {
@@ -298,6 +303,9 @@ impl Command {
     pub fn get_chroot(&self) -> Option<&CStr> {
         self.chroot.as_deref()
     }
+    pub fn get_resolve_in_parent_path(&self) -> bool {
+        self.resolve_in_parent_path
+    }
 
     pub fn get_closures(&mut self) -> &mut Vec<Box<dyn FnMut() -> io::Result<()> + Send + Sync>> {
         &mut self.closures

library/std/src/sys/process/unix/unix.rs

@@ -276,7 +276,7 @@ impl Command {
     unsafe fn do_exec(
         &mut self,
         stdio: ChildPipes,
-        maybe_envp: Option<&CStringArray>,
+        mut maybe_envp: Option<&CStringArray>,
     ) -> Result<!, io::Error> {
         use crate::sys::{self, cvt_r};
 
@@ -378,13 +378,73 @@ impl Command {
             callback()?;
         }
 
-        // Although we're performing an exec here we may also return with an
-        // error from this function (without actually exec'ing) in which case we
-        // want to be sure to restore the global environment back to what it
-        // once was, ensuring that our temporary override, when free'd, doesn't
-        // corrupt our process's environment.
-        let mut _reset = None;
-        if let Some(envp) = maybe_envp {
+        if let Some(envp) = maybe_envp
+            && self.get_resolve_in_parent_path()
+            && self.env_saw_path()
+            && self.get_program_kind() == ProgramKind::PathLookup
+        {
+            use crate::ffi::CStr;
+            // execvpe is a gnu extension...
+            #[cfg(all(target_os = "linux", target_env = "gnu"))]
+            unsafe fn exec_with_env(
+                program: &CStr,
+                args: &CStringArray,
+                envp: &CStringArray,
+            ) -> libc::c_int {
+                unsafe { libc::execvpe(program.as_ptr(), args.as_ptr(), envp.as_ptr()) }
+            }
+
+            // ...so if we're not gnu then use our own implementation.
+            #[cfg(not(all(target_os = "linux", target_env = "gnu")))]
+            unsafe fn exec_with_env(
+                program: &CStr,
+                args: &CStringArray,
+                envp: &CStringArray,
+            ) -> libc::c_int {
+                unsafe {
+                    let name = program.to_bytes();
+                    let mut buffer =
+                        [const { mem::MaybeUninit::<u8>::uninit() }; libc::PATH_MAX as usize];
+                    let mut environ = *sys::env::environ();
+                    // Search the environment for PATH and, if found,
+                    // search the paths for the executable by trying to execve each candidate.
+                    while !(*environ).is_null() {
+                        let kv = CStr::from_ptr(*environ);
+                        if let Some(value) = kv.to_bytes().strip_prefix(b"PATH=") {
+                            for path in value.split(|&b| b == b':') {
+                                if buffer.len() - 2 >= path.len().saturating_add(name.len()) {
+                                    let buf_ptr = buffer.as_mut_ptr().cast::<u8>();
+                                    let mut offset = 0;
+                                    if !path.is_empty() {
+                                        buf_ptr.copy_from(path.as_ptr(), path.len());
+                                        offset += path.len();
+                                        if path.last() != Some(&b'/') {
+                                            *buf_ptr.add(path.len()) = b'/';
+                                            offset += 1;
+                                        }
+                                    }
+                                    buf_ptr.add(offset).copy_from(name.as_ptr(), name.len());
+                                    offset += name.len();
+                                    *buf_ptr.add(offset) = 0;
+                                    libc::execve(buf_ptr.cast(), args.as_ptr(), envp.as_ptr());
+                                }
+                            }
+                            break;
+                        }
+                        environ = environ.add(1);
+                    }
+                    // If execve is successful then it'll never return, thus we'll never reach this point.
+                    -1
+                }
+            }
+            exec_with_env(self.get_program_cstr(), self.get_argv(), envp);
+        } else if let Some(envp) = maybe_envp {
+            // Although we're performing an exec here we may also return with an
+            // error from this function (without actually exec'ing) in which case we
+            // want to be sure to restore the global environment back to what it
+            // once was, ensuring that our temporary override, when free'd, doesn't
+            // corrupt our process's environment.
+            let mut _reset = None;
             struct Reset(*const *const libc::c_char);
 
             impl Drop for Reset {
@@ -397,9 +457,8 @@ impl Command {
 
             _reset = Some(Reset(*sys::env::environ()));
             *sys::env::environ() = envp.as_ptr();
+            libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
         }
-
-        libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
         Err(io::Error::last_os_error())
     }
 
@@ -453,7 +512,9 @@ impl Command {
 
         if self.get_gid().is_some()
             || self.get_uid().is_some()
-            || (self.env_saw_path() && !self.program_is_path())
+            || (!self.get_resolve_in_parent_path()
+                && self.env_saw_path()
+                && !self.program_is_path())
             || !self.get_closures().is_empty()
             || self.get_groups().is_some()
             || self.get_chroot().is_some()

library/std/src/sys/process/unsupported.rs

@@ -21,6 +21,7 @@ pub struct Command {
     stdin: Option<Stdio>,
     stdout: Option<Stdio>,
     stderr: Option<Stdio>,
+    force_parent_path: bool,
 }
 
 // passed back to std::process with the pipes connected to the child, if any
@@ -52,6 +53,7 @@ impl Command {
             stdin: None,
             stdout: None,
             stderr: None,
+            force_parent_path: false,
         }
     }
 
@@ -79,6 +81,10 @@ impl Command {
         self.stderr = Some(stderr);
     }
 
+    pub fn resolve_in_parent_path(&mut self, use_parent: bool) {
+        self.force_parent_path = use_parent;
+    }
+
     pub fn get_program(&self) -> &OsStr {
         &self.program
     }

library/std/src/sys/process/windows.rs

@@ -158,6 +158,7 @@ pub struct Command {
     startupinfo_fullscreen: bool,
     startupinfo_untrusted_source: bool,
     startupinfo_force_feedback: Option<bool>,
+    force_parent_path: bool,
 }
 
 pub enum Stdio {
@@ -192,6 +193,7 @@ impl Command {
             startupinfo_fullscreen: false,
             startupinfo_untrusted_source: false,
             startupinfo_force_feedback: None,
+            force_parent_path: false,
         }
     }
 
@@ -224,6 +226,10 @@ impl Command {
         self.force_quotes_enabled = enabled;
     }
 
+    pub fn resolve_in_parent_path(&mut self, use_parent: bool) {
+        self.force_parent_path = use_parent;
+    }
+
     pub fn raw_arg(&mut self, command_str_to_append: &OsStr) {
         self.args.push(Arg::Raw(command_str_to_append.to_os_string()))
     }
@@ -274,7 +280,10 @@ impl Command {
         let env_saw_path = self.env.have_changed_path();
         let maybe_env = self.env.capture_if_changed();
 
-        let child_paths = if env_saw_path && let Some(env) = maybe_env.as_ref() {
+        let child_paths = if env_saw_path
+            && !self.force_parent_path
+            && let Some(env) = maybe_env.as_ref()
+        {
             env.get(&EnvKey::new("PATH")).map(|s| s.as_os_str())
         } else {
             None