diff --git a/src/header/fcntl/mod.rs b/src/header/fcntl/mod.rs
index 94a39ab..7ec147f 100644
--- a/src/header/fcntl/mod.rs
+++ b/src/header/fcntl/mod.rs
@@ -140,6 +140,9 @@ unsafe extern "C" fn fcntl(fd: c_int, cmd: c_int, args: ...) -> CIntCountResult
     let file = RawFile::e_try_from(fd)?;
 
     match cmd {
+        // TODO implement these somehow?
+        F_GETFD => CIntCountResult(0),
+        F_SETFD => CIntCountResult(0),
         _ => todo!("fcntl({}, {}, ...)", fd, cmd),
     }
 }
diff --git a/src/header/sys_stat/mod.rs b/src/header/sys_stat/mod.rs
index 2fc92f2..2651b97 100644
--- a/src/header/sys_stat/mod.rs
+++ b/src/header/sys_stat/mod.rs
@@ -4,7 +4,7 @@ use yggdrasil_rt::io::{FileAttr, FileMode, FileType, RawFd};
 
 use crate::{
     error::{CIntZeroResult, TryFromExt},
-    io,
+    io, process,
     util::{self, Nullable},
 };
 
@@ -74,8 +74,8 @@ impl From<FileAttr> for stat {
         }
         st.st_size = value.size.try_into().unwrap();
         // TODO
-        st.st_uid = 0;
-        st.st_gid = 0;
+        st.st_uid = u32::from(value.uid).try_into().unwrap();
+        st.st_gid = u32::from(value.gid).try_into().unwrap();
         // TODO
         st.st_blksize = 512;
         st.st_blocks = (st.st_size + 511) / 512;
@@ -108,7 +108,9 @@ unsafe extern "C" fn fchmodat(
 
 #[no_mangle]
 unsafe extern "C" fn umask(mode: mode_t) -> mode_t {
-    todo!()
+    let new = FileMode::new((mode as u32) & 0o777);
+    let old = process::update_umask(new);
+    old.bits() as mode_t
 }
 
 // Create stuff
diff --git a/src/io/buffered.rs b/src/io/buffered.rs
index 7493a6f..3ed5c85 100644
--- a/src/io/buffered.rs
+++ b/src/io/buffered.rs
@@ -150,6 +150,7 @@ impl<W: Write> Write for BufWriter<W> {
     fn write(&mut self, mut data: &[u8]) -> EResult<usize> {
         if data.len() + self.buffer.len() >= self.buffer.capacity() {
             self.flush()?;
+            assert_eq!(self.buffer.len(), 0);
         }
 
         let len = data.len();
@@ -167,7 +168,7 @@ impl<W: Write> Write for BufWriter<W> {
         }
 
         // Store the data in the buffer
-        assert!(data.len() < self.buffer.capacity());
+        assert!(data.len() <= self.buffer.capacity());
         self.buffer.extend_from_slice(data);
         EResult::Ok(len)
     }
diff --git a/src/process.rs b/src/process.rs
index 4cd789e..08b5b8a 100644
--- a/src/process.rs
+++ b/src/process.rs
@@ -2,7 +2,8 @@ use core::{ffi::c_char, ptr::null_mut, slice::memchr};
 
 use alloc::{ffi::CString, vec::Vec};
 use yggdrasil_rt::{
-    process::{ExitCode, ProgramArgumentInner, Signal},
+    io::FileMode,
+    process::{ExitCode, ProcessInfoElement, ProgramArgumentInner, Signal},
     sys as syscall,
 };
 
@@ -81,6 +82,32 @@ pub fn abort() -> ! {
     }
 }
 
+pub fn get_process_info(info: &mut ProcessInfoElement) -> EResult<()> {
+    unsafe {
+        syscall::get_process_info(info)?;
+    }
+    EResult::Ok(())
+}
+
+pub fn set_process_info(info: &ProcessInfoElement) -> EResult<()> {
+    unsafe {
+        syscall::set_process_info(info)?;
+    }
+    EResult::Ok(())
+}
+
+pub fn update_umask(new: FileMode) -> FileMode {
+    let mut old = ProcessInfoElement::Umask(FileMode::empty());
+    let new = ProcessInfoElement::Umask(new);
+
+    get_process_info(&mut old).unwrap();
+    set_process_info(&new).unwrap();
+
+    let ProcessInfoElement::Umask(old) = old;
+
+    old
+}
+
 // Env
 
 static mut ENVS: Vec<CString> = Vec::new();