Make `uname` always safe

This fixes several issues with the current `uname` bindings:

  - Do not ignore `uname` errors; at least on glibc `uname` can fail,
    so now it returns a `Result` instead of assuming that the call
    will always succeed.

  - Do not assume `uname` will initialize every member of `utsname`;
    not every implementation initializes every field, so internally
    the struct is now zero-initialized.

  - Do not blindly assume strings returned by `uname` will always be valid UTF-8;
    `UtsName`'s accessors will now return `&OsStr`s instead of `&str`s.

1 files changed, 29 insertions, 27 deletions

diff --git a/src/sys/utsname.rs b/src/sys/utsname.rs
index 98edee04..5bd3a539 100644
--- a/src/sys/utsname.rs
+++ b/src/sys/utsname.rs
@@ -1,8 +1,9 @@
 //! Get system identification
 use std::mem;
-use libc::{self, c_char};
-use std::ffi::CStr;
-use std::str::from_utf8_unchecked;
+use std::os::unix::ffi::OsStrExt;
+use std::ffi::OsStr;
+use libc::c_char;
+use crate::{Errno, Result};
 
 /// Describes the running system.  Return type of [`uname`].
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
@@ -10,47 +11,48 @@ use std::str::from_utf8_unchecked;
 pub struct UtsName(libc::utsname);
 
 impl UtsName {
-    /// Name of the operating system implementation
-    pub fn sysname(&self) -> &str {
-        to_str(&(&self.0.sysname as *const c_char ) as *const *const c_char)
+    /// Name of the operating system implementation.
+    pub fn sysname(&self) -> &OsStr {
+        cast_and_trim(&self.0.sysname)
     }
 
     /// Network name of this machine.
-    pub fn nodename(&self) -> &str {
-        to_str(&(&self.0.nodename as *const c_char ) as *const *const c_char)
+    pub fn nodename(&self) -> &OsStr {
+        cast_and_trim(&self.0.nodename)
     }
 
     /// Release level of the operating system.
-    pub fn release(&self) -> &str {
-        to_str(&(&self.0.release as *const c_char ) as *const *const c_char)
+    pub fn release(&self) -> &OsStr {
+        cast_and_trim(&self.0.release)
     }
 
     /// Version level of the operating system.
-    pub fn version(&self) -> &str {
-        to_str(&(&self.0.version as *const c_char ) as *const *const c_char)
+    pub fn version(&self) -> &OsStr {
+        cast_and_trim(&self.0.version)
     }
 
     /// Machine hardware platform.
-    pub fn machine(&self) -> &str {
-        to_str(&(&self.0.machine as *const c_char ) as *const *const c_char)
+    pub fn machine(&self) -> &OsStr {
+        cast_and_trim(&self.0.machine)
     }
 }
 
 /// Get system identification
-pub fn uname() -> UtsName {
+pub fn uname() -> Result<UtsName> {
     unsafe {
-        let mut ret = mem::MaybeUninit::uninit();
-        libc::uname(ret.as_mut_ptr());
-        UtsName(ret.assume_init())
+        let mut ret = mem::MaybeUninit::zeroed();
+        Errno::result(libc::uname(ret.as_mut_ptr()))?;
+        Ok(UtsName(ret.assume_init()))
     }
 }
 
-#[inline]
-fn to_str<'a>(s: *const *const c_char) -> &'a str {
-    unsafe {
-        let res = CStr::from_ptr(*s).to_bytes();
-        from_utf8_unchecked(res)
-    }
+fn cast_and_trim(slice: &[c_char]) -> &OsStr {
+    let length = slice.iter().position(|&byte| byte == 0).unwrap_or(slice.len());
+    let bytes = unsafe {
+        std::slice::from_raw_parts(slice.as_ptr().cast(), length)
+    };
+
+    OsStr::from_bytes(bytes)
 }
 
 #[cfg(test)]
@@ -58,18 +60,18 @@ mod test {
     #[cfg(target_os = "linux")]
     #[test]
     pub fn test_uname_linux() {
-        assert_eq!(super::uname().sysname(), "Linux");
+        assert_eq!(super::uname().unwrap().sysname(), "Linux");
     }
 
     #[cfg(any(target_os = "macos", target_os = "ios"))]
     #[test]
     pub fn test_uname_darwin() {
-        assert_eq!(super::uname().sysname(), "Darwin");
+        assert_eq!(super::uname().unwrap().sysname(), "Darwin");
     }
 
     #[cfg(target_os = "freebsd")]
     #[test]
     pub fn test_uname_freebsd() {
-        assert_eq!(super::uname().sysname(), "FreeBSD");
+        assert_eq!(super::uname().unwrap().sysname(), "FreeBSD");
     }
 }