fs: copy: Add EPERM to fallback error conditions

Fixes rust-lang#51266

Author: nicokoch

Diff for: src/libstd/sys/unix/fs.rs

@@ -890,8 +890,11 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
                     )
             };
             if let Err(ref copy_err) = copy_result {
-                if let Some(libc::ENOSYS) = copy_err.raw_os_error() {
-                    HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
+                match copy_err.raw_os_error() {
+                    Some(libc::ENOSYS) | Some(libc::EPERM) => {
+                        HAS_COPY_FILE_RANGE.store(false, Ordering::Relaxed);
+                    }
+                    _ => {}
                 }
             }
             copy_result
@@ -902,9 +905,13 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
             Ok(ret) => written += ret as u64,
             Err(err) => {
                 match err.raw_os_error() {
-                    Some(os_err) if os_err == libc::ENOSYS || os_err == libc::EXDEV => {
-                        // Either kernel is too old or the files are not mounted on the same fs.
-                        // Try again with fallback method
+                    Some(os_err) if os_err == libc::ENOSYS
+                                 || os_err == libc::EXDEV
+                                 || os_err == libc::EPERM => {
+                        // Try fallback io::copy if either:
+                        // - Kernel version is < 4.5 (ENOSYS)
+                        // - Files are mounted on different fs (EXDEV)
+                        // - copy_file_range is disallowed, for example by seccomp (EPERM)
                         assert_eq!(written, 0);
                         let ret = io::copy(&mut reader, &mut writer)?;
                         writer.set_permissions(perm)?;