Close non-stdio file handles when daemonizing

Cargo.toml

@@ -134,6 +134,7 @@ test-case = "3.3.1"
 thirtyfour_sync = "0.27"
 
 [target.'cfg(unix)'.dependencies]
+close_fds = "0.3.2"
 daemonize = "0.5"
 
 [target.'cfg(not(target_os = "freebsd"))'.dependencies.libmount]

src/bin/sccache-dist/main.rs

@@ -212,7 +212,7 @@ fn run(command: Command) -> Result<i32> {
                 }
             };
 
-            daemonize()?;
+            daemonize(None)?;
             let scheduler = Scheduler::new();
             let http_scheduler = dist::http::Scheduler::new(
                 public_addr,

src/commands.rs

@@ -126,26 +126,6 @@ fn run_server_process(startup_timeout: Option<Duration>) -> Result<ServerStartup
     })
 }
 
-#[cfg(not(windows))]
-fn redirect_stderr(f: File) {
-    use libc::dup2;
-    use std::os::unix::io::IntoRawFd;
-    // Ignore errors here.
-    unsafe {
-        dup2(f.into_raw_fd(), 2);
-    }
-}
-
-#[cfg(windows)]
-fn redirect_stderr(f: File) {
-    use std::os::windows::io::IntoRawHandle;
-    use windows_sys::Win32::System::Console::{SetStdHandle, STD_ERROR_HANDLE};
-    // Ignore errors here.
-    unsafe {
-        SetStdHandle(STD_ERROR_HANDLE, f.into_raw_handle() as _);
-    }
-}
-
 /// Create the log file and return an error if cannot be created
 fn create_error_log() -> Result<File> {
     trace!("Create the log file");
@@ -165,13 +145,6 @@ fn create_error_log() -> Result<File> {
     Ok(f)
 }
 
-/// If `SCCACHE_ERROR_LOG` is set, redirect stderr to it.
-fn redirect_error_log(f: File) -> Result<()> {
-    debug!("redirecting stderr into {:?}", f);
-    redirect_stderr(f);
-    Ok(())
-}
-
 /// Re-execute the current executable as a background server.
 #[cfg(windows)]
 fn run_server_process(startup_timeout: Option<Duration>) -> Result<ServerStartup> {
@@ -654,14 +627,15 @@ pub fn run_command(cmd: Command) -> Result<i32> {
         }
         Command::InternalStartServer => {
             trace!("Command::InternalStartServer");
+            // If `SCCACHE_ERROR_LOG` is set, redirect stderr to it.
             if env::var("SCCACHE_ERROR_LOG").is_ok() {
                 let f = create_error_log()?;
+                debug!("redirecting stderr into {:?}", f);
                 // Can't report failure here, we're already daemonized.
-                daemonize()?;
-                redirect_error_log(f)?;
+                daemonize(Some(f))?;
             } else {
                 // We aren't asking for a log file
-                daemonize()?;
+                daemonize(None)?;
             }
             server::start_server(config, &get_addr())?;
         }

src/util.rs

@@ -841,7 +841,7 @@ impl Hasher for HashToDigest<'_> {
 
 /// Pipe `cmd`'s stdio to `/dev/null`, unless a specific env var is set.
 #[cfg(not(windows))]
-pub fn daemonize() -> Result<()> {
+pub fn daemonize(log_file: Option<File>) -> Result<()> {
     use crate::jobserver::discard_inherited_jobserver;
     use daemonize::Daemonize;
     use std::env;
@@ -850,7 +850,18 @@ pub fn daemonize() -> Result<()> {
     match env::var("SCCACHE_NO_DAEMON") {
         Ok(ref val) if val == "1" => {}
         _ => {
-            Daemonize::new().start().context("failed to daemonize")?;
+            Daemonize::new()
+                .stderr(
+                    log_file
+                        .map(|f| f.into_parts().0.into())
+                        .unwrap_or_else(daemonize::Stdio::devnull),
+                )
+                .start()
+                .context("failed to daemonize")?;
+            // Be extra-zealous and clase all non-stdio file descriptors.
+            unsafe {
+                close_fds::close_open_fds(3, &[]);
+            }
         }
     }
 
@@ -926,12 +937,26 @@ pub fn daemonize() -> Result<()> {
     }
 }
 
-/// This is a no-op on Windows.
+/// Daemonizing is a no-op on Windows, but we still must set the log file as
+/// stderr.
 #[cfg(windows)]
-pub fn daemonize() -> Result<()> {
+pub fn daemonize(log_file: Option<File>) -> Result<()> {
+    if let Some(log_file) = log_file {
+        redirect_stderr(log_file);
+    }
     Ok(())
 }
 
+#[cfg(windows)]
+fn redirect_stderr(f: File) {
+    use std::os::windows::io::IntoRawHandle;
+    use windows_sys::Win32::System::Console::{SetStdHandle, STD_ERROR_HANDLE};
+    // Ignore errors here.
+    unsafe {
+        SetStdHandle(STD_ERROR_HANDLE, f.into_raw_handle() as _);
+    }
+}
+
 /// Disable connection pool to avoid broken connection between runtime
 ///
 /// # TODO