std: fix unix socket address panic on a full sun_path

library/std/src/os/unix/net/addr.rs

@@ -123,6 +123,8 @@ impl SocketAddr {
                 .map_or(len, |new_len| (new_len + SUN_PATH_OFFSET) as libc::socklen_t);
         }
 
+        len = len.min(size_of::<libc::sockaddr_un>() as libc::socklen_t);
+
         if len == 0 {
             // When there is a datagram from unnamed unix socket
             // linux returns zero bytes of address

library/std/src/os/unix/net/tests.rs

@@ -52,6 +52,25 @@ fn sock_addr_without_trailing_nul() {
     assert_eq!(address.as_pathname(), Some(Path::new("/path/to/socket")));
 }
 
+#[test]
+#[cfg(any(target_os = "android", target_os = "linux"))]
+fn sock_addr_pathname_fills_sun_path() {
+    use crate::ffi::OsStr;
+    use crate::os::unix::ffi::OsStrExt;
+
+    let mut addr: libc::sockaddr_un = unsafe { crate::mem::zeroed() };
+    addr.sun_family = libc::AF_UNIX as libc::sa_family_t;
+    let mut path = vec![b'a'; addr.sun_path.len()];
+    path[0] = b'/';
+    for (dst, &src) in addr.sun_path.iter_mut().zip(&path) {
+        *dst = src as _;
+    }
+    let offset = crate::mem::offset_of!(libc::sockaddr_un, sun_path);
+
+    let address = or_panic!(SocketAddr::from_parts(addr, (offset + path.len() + 1) as _));
+    assert_eq!(address.as_pathname(), Some(Path::new(OsStr::from_bytes(&path))));
+}
+
 #[test]
 #[cfg_attr(target_os = "android", ignore)] // Android SELinux rules prevent creating Unix sockets
 #[cfg_attr(target_os = "vxworks", ignore = "Unix sockets are not implemented in VxWorks")]